Conversation with Marije, March 2017

After an inspiring talk with Marije on March 3rd, I set out to write this blog post to sum up what we had been talking about. As it happens (and has happened before), Marije had a lot of pointer to other related works and writings. Only after I had looked at the material she pointed to, and reflected upon it, did I get around to writing this blog post. So substantial parts of it contains more of a reflection after the conversation, rather than an actual report of what was said directly.
Marije mentiones we have done a lot of work, it is inspiring, solid, looks good.

Agency, focus of attention

One of the first subjects in our conversation was how we relate to the instrument. For performers: How does it work? Does it work? (does it do what we say/think it does?) What do I control? What controls me? when successful it might constitute a 3rd agency, a shared feeling, mutual control. Not acting as a single musician, but as an ensemble. The same observation can of course be made (when playing) in acoustic ensembles too, but it is connected differently in our setting.

Direct/indirect control. Play music or generate control signals? Very direct and one-dimensional mappings can easily feel like playing to generate control signals. Some control signals can be formed (by analyzing) over longer time spans, as they represent more of a “situation” than an immediate “snapshot”. Perhaps just as interesting for a musician to outline a situation over time, than to simply control one sonic dimension by acting on another?

Out-of-time’d-ness, relating to the different perceptions of the performative role experienced in IR recording (see posts on convolution sessions here, here and here). A similar experience can be identified within other forms of live sampling. to some degree recognizable with all sorts of live processing as an instrumental activity. For the live processing performer: a detached-ness of control as opposed to directly playing each event.

Contrived and artificial mappings. I asked whether the analyzer-modulation mappings are perhaps too contrived, too “made up”? Marije replying that everything we do with electronic music instrument design (and mapping) is to some degree made up. It is always artibrary, design decisions, something made up. There is not one “real” way, no physical necessity or limitation that determines what the “correct” mapping is. As such, there are only mappings that emphasize different aspects of performance and interaction, new ideas that might seem “contrived” can contain yet-to-be-seen areas of such emphasis. Composition is in these connections. For longer pieces one might want variation in mapping. For example, in the combined instrument created by voice and drums in some of our research sessions. Depending on combination and how it is played, the mapping might wear out over time, so one might want to change it during one musical piece.

Limitation. In January I did a presentation at UC Irvine, for an audience well trained in live processing and electronic music performance. One of the perspectives mentioned there was that the cross-adaptive mapping could also be viewed as a limitation. One could claim that all of these modulations that we can perform cross-adaptively could have been manually controlled, an with much more musical freedom if manually controlled. Still, the crossadaptive situation provides another kind of dynamic. The acoustic instrument is immediate and multidimensional, providing a nuanced and intuitive interface. We can tap into that. As an example as to how the interfacne changes the expression, look at how we (Marije) use accelerometers over 3 axes of motion: one could produce the same exact same control signals using 3 separate faders, but the agency of control, the feeling, the expressivity, the dynamic is different with accelerometers that it is with faders. It is different to play, and this will produce different results. The limitations (of an interface or a mapping) can be viewed as something interesting, just as much as something that inhibits.

Analyzer noise and flakyness

One thing that have concerned me lately is the fact that the analyzer is sometimes too sensitive to minor variations in the signal. Mathematical differences sometimes occur on a different scale than the expressive differences. One example is the rhythm analyzer, the way I think it is too noisy and unreliable, seen in the light of the practical use in session, where the musicians found it very appropriate and controllable.
Marije reminds me that in the live performance setting, small accidents and surprises are inspiring. In a production setting perhaps not so much. Musicians are trained to embrace the imperfections of, and characteristic traits of their instument, so it is natural for them to also respond in a similar manner to imperfections in the adaptive and crossadaptive control methods. This makes me reflect if there is a research methodology of accidents(?), on how to understand the art of the accident, understand the failure of the algorithm, like in glitch, circuit bending, and other art forms relating to distilling and refining “the unwanted”.

Rhythm analysis

I will refine the rhythm analysis, it seems promising as a measure
of musical expressivity. I have some ideas of maintaining several parallel hypotheses on how to interpret input, based on previous rhythm research. some of this comes from “Machine Musicianship” by Robert Rowe, some from readin a UCSD dissertation by Michelle L. Daniels: “An Ensemble Framework for Real-Time Beat Tracking”. I am currently trying to distill these into a simplest possible method of rhythm analysis for our purposes. So I ask Marije on ideas on how to refine the rhythm analyzer. Rhythm can be one parameters that outlines “a situation” just as much as it creates a “snapshot” (recall the discussion of agency and direct/indirect control, above). One thing we may want to extract is slower shifts, from one situation to another. My concerns that it takes too long to analyze a pattern (well, at least as long as the pattern itself, which might be several seconds) can then be regarded less of a concern, since we are not primarily looking for immediate output. Still, I will attempt to minimize the latency of rhythm analysis, so that any delay in response is due to aestethic choice, and not so much limited by the technology. She also mentions the other Nick Collins. I realize that he’s the one behind the bbcut algorithm also found in Csound. I’ve used a lot a long time ago. Collins has written a library for feature extraction within SuperCollider. To some degree there is overlap with feature extraction on our Analyzer plugin. Collins invokes external programs to produce similarity matrices, something that might be useful for our purposes as well, as a means of finding temporal patterns in the input. In terms of rhythm analysis, it is based on beat tracking as is common. While we in our rhythm analysis attempts at *not relying* on beat tracking, we could still perhaps implement it, if nothing else so to use it as a measure of beat tracking confidence (assuming this as a very coarse distinction between beat based and more temporally free music.
Another perspective on rhythm analysis can also perhaps be gained from Clarence Barlow’s interest in ratios. The ratio book is available online, as is a lot of his other writings.  Barlow states “In the case of ametric music, all pulses are equally probable”… which leads me to think that any sort of statistical analysis, frequency of occurence of observed inter-onset times, will start to give indications of “what this is”… to lift it slowly out of the white-noise mud of equal probabilities.

Barlow uses the “Indispensability formula“, for relating the importance of each subdivision within a given meter. Perhaps we could invert this somehow to give a general measure of “subdivided-ness“?. We’re not really interested in finding the meter, but the patterns of subdivision is nonetheless of interest. He also use the “Indigestibility formula” for ratios, based on prime-ness, suggests also a cultural digestability limit around 10 (10:11, 11:12, 12:13 …). I’ve been pondering different ways of ordering the complexity of different integer ratios, such as different trhythmic subdivisions. The indigesibility formula might be one way to approach it, but reading further in the ratio book, the writing of Demetrios E. Lekkas leads me to think of another way to sort the subdivisions into increasing complexity:

Lekkas describes the traditional manner of writing down all rational numbers by starting with 1/1 (p 38), then increasing the numerator by one, then going through all denominators from 1 up to the nominator, skipping fracions that can be simplified since they represent numbers earlier represented. This ordering does not imply any relation to complexity of the ratios produced. If tried to use it as such, one problem with this ordering is that it determines that subdividing in 3 is less complex than subdividing in 4. Intuitively, I’d say a rhythmic subdivision in 3 is more complex than a further subdivision of the first established subdivision in 2. Now, could we, to try to find a measure of complexity, assume that divisions further apart from any previous established subdivision are simpler than the ones creating closely spaced divisions(?). So, when dividing 1/1 in 2, we get a value at 0.5 (in addition to 0.0 and 1.0, which we omit for brevity). Then, trying to decide what is the next further division is the most complex, we try out all possible further subdivision up to some limit, look at the resulting values and their distances to already excisting values.
Dividing in 3 give 0.33 and 0.66 (approx), while dividing in 4 give the (new) values 0.25 and 0.75. Dividing by 5 gives new values at .2 and .4, by 6 is unnecessary as it does not produce any larger distances than already covered by 3. Divide by 7 gives values at .142, 0.285 and .428. Divide by 8 is unnecessary as it does not produce any values of larger distance than the divide by 4.
The lowest distance introduced by dividing in 3 is 0.33 to 0.5, a distance of approx 0.17. The lowest distance introduced by dividing in 4 is from 0.25 to 0.5, a distance of 0.25. Dividing into 4 is thus less complex. Checking the divide by 5 and 7 can be left as an exercise to the reader.
Then we go on to the next subdivision, as we now have a grid of 1/2 plus 1/4, with values at 0.25, 0.5 and 0.75. The next two alternatives (in increasing numeric order) is division by 3 or division by 5. Division by 3 gives a smallest distance (to our current grid) from 0.25 to 0.33 = 0.08. Division by 5 gives a smallest distance from 0.2 to 0.25 = 0.05. We conclude that division by 3 is less complex. But wait, let’s check division by 8 too while we’re at it also here, leaving divide by 6 and 7 as an exercise to the reader). Division by 8, in relation to our current grid (.25, .5, .75) gives a smallest distance of 0.125. This is larger than the smallest distance produced by division in 3 (0.08), so we choose 8 as our next number in increasing order of complexity.
Following up on this method, using a highest subdivision of 8, eventually gives us this order 2,4,8,3,6,5,7 as subdivisions in increasing order of complexity. This coincides with my intuition of rhythmic complexity, and can be reached by the simple procedure outlined above. We could also use the same procedure to determine the exact value of complexity for each of these subdivisions, as a means to create an output “value of complexity” for integer ratios. As a side note to myself, check how this will differ from using Tenney height or Benedetti height as I’ve used earlier in the Analyzer.

On the justification for coming up with this procedure I might lean lightly on Lekkas again: “If you want to compare them you just have to come up with your own intuitive formula…deciding which one is more important…That would not be mathematical. Mind you, it’s non-mathematical, but not wrong.” (Ratio book p 40)
Much of the book relates to ratios as in pitch ratios and tuning. Even though we can view pitch and rhythm as activity within the same scale, as vibrations/activations at different frequencies, the perception of pitch is further complicated by the anatomy of our inner ear (critical bands), and by cultural aspects and habituation. Assumedly, these additional considerations should not be used to infer complexity of rhythmic activity. We can not directly use harmonicity of pitch as a measure of the harmonicity of rhythm, even though it might *to some extent* hold true (and I have used this measure up until now in the Analyzer).

Further writings by Barlow on this subject can also be found in his On Musiquantics. “Can the simplicity of a ratio be expressed quantitatively?” (s 38), related to the indegestability formula. See also how “metric field strength”  (p 44), relates to the indispensability formula. The section from p 38-47 concerns this issue, as well as his “Formulæ for Harmonicity” p 24, (part II), with Interval Size, Ratios and Harmonic Intensity on the following pages. For pitch, the critical bandwidth (p 48) is relevant but we could discuss if not the “larger distance created by a subdivision” as I outlined above is more appropriate for rhythmic ratios.

Instrumentality

The 3Dmin book “Musical Instruments in the 21st Century” explores various notions of what an instrument can be, for example the instrument as a possibility space. Lopes/Hoelzl/de Campo, in their many-fest “favour variety and surprise over logical continuation” and “enjoy the moment we lose control and gain influence”. We can relate this to our recent reflections on how performers in our project thrive in a setting where the analysis meethods are somewhat noisy and chaotic. The essence being they can control the general trend of modulation, but still be surprised and disturbed” by the immediate details. Here we again encounter methods of the “less controllable”: circuit bending, glitch, autopoietic (self-modulating) instruments, meta-control techniques (de Campo), and similarly the XY interface for our own Hadron synthesizer, to mention a few apparent directions. The 3DMIN book also has a chapter by Daphna Naphtali on using live processing as an instrument. She identifies some potential problems about the invisible instrument. One problem, according to Naptali, is that it can be difficult to identify the contribution (of the performer operating it). One could argue that invisibility is not necessarily a problem(?), but indeed it (invisibility and the intangible) is a characteristic trait of the kind of instruments that we are dealing with, be it for live processing as controlled by an electronnic musician, or for crossadaptive processing as controlled by the acoustic musicians.

Marije also has a chapter in this book, on the blurring boundaries between composition, instrument design, and improvisation. …”the algorithm for the translation of sensor data into music control data is a major artistic
area; the definition of these relationships is part of the composition of a piece” Waisvisz 1999, cited by Marije

Using adaptive effects as a learning strategy

In light of the complexity of crossadaptive effects, the simpler adaptive effects could be used as a means of familiarization for both performers and “mapping designers” alike. Getting to know how the analyzer reacts to different source material, and how to map the signals in a musically effective manner. The adaptive use case is also more easily adaptable to a mixing situation, for composed music, and any other kind of repeatable situation. The analyzer methods can be calibrated and tuned more easily for each specific source instrument. Perhaps we could also look at a possible methodology for familiarization, how do we most efficiently learn to know these feature-to-modulator mappings. Revising the literature on adaptive audio effects (Verfaille etc) in the light of our current status and reflections might be a good idea.

Performers utilizing adaptive control

Similarly, it might be a good idea to get on touch with environments and performers using adaptive techniques as part of their setup. Marije reminded me that Jos Zwaanenburg and his students at the Conservatorium of Amsterdam might have more examples of musicians using adaptive control techniques. I met Jos some years ago, and contacted him again via email now. Hans Leeouw is another Dutch performer working with adaptive control techniques.  His 2009 NIME article mentions no adaptive control, but has a beautiful statement on the design of mappings: “…when the connection between controller and sound is too obvious the experience of ‘hearing what you see’ easily becomes ‘cheesy’ and ‘shallow’. One of the beauties of acoustic music is hearing and seeing the mastery of a skilled instrumentalist in controlling an instrument that has inherent chaotic behaviour “. In the 2012 NIME article he mentions audio analyses for control. I Contacted Hans to get more details and updated information about what he is using. Via email he tells that he use noise/sinusoidal balance as a control both for signal routing (trumpet sound routed to different filters), and also to reconfigure the mapping of his controllers (as appropriate for the different filter configuration). He mentions that the analyzed transition from noise to sinusoidal can be sharp, and that additional filtering is needed to geet a smooth transition. A particularly interesting area occurs when the routing and mapping is in this intermediate area, where both modes of processing and mapping are partly in effect.

As an example of on researcher/performer that has explored voice control, Marije mentioned Dan Stowell.
Nor surprisingly, he’s also done his research in the context of QMUL. Browsing his thesis, I note some useful terms for ranking extracted features, as he writes about *perceptual relevance*, *robustness*, and *independence*. His experiments on ranking the different features are not conclusive, as “none of the experiments in themselves will suggest a specific compact feature set”. This indication coincides with our own experience so far as well, that different instruments and different applications require different subsets of features. He does however mention spectral centroid, to be particularly useful. We have initially not used this so much due to a high degree of temporal fluctuation. Similarly, he mentions spectral spread, where we have so far used more spectral flatness and spectral flux. This also reminds me of recent discussions on the Csound list regarding different implementations of the analysis of spectral flux (difference from frame to frame or normalized inverse correlation), it might be a good idea to test the different implementations to see if we can have several variations on this measure, since we have found it useful in some but not all of our application areas. Stowell also mentions log attack time, which we should revisit and see how we can apply or reformulate to fit our use cases. A measure that we haven’t considered so far is delta MFCCs, the temporal variation within each cepstral band. Intuitively it seems to me this couldd be an alternative to spectral flux, even though Stowell have found it not to have a significant mutual information bit (delta MFCC to spectral flux). In fact the Delta MFCCs have little MI with any other features whatsoever, although this could be related to implementation detail (decorrelation). He also finds that Delta MFCC have low robustness, but we should try implementing it and see what it give us. Finally, he also mentions *clarity* as a spectral measure, in connectino to pitch analysis, defined as “the normalised strength of the second peak of the autocorrelation trace [McLeod and Wyvill, 2005]”. It is deemed a quite robust measure, and we could most probably implement this with ease and test it.

 

Seminar: Mixing and timbral character

Online conversation with Gary Bromham (London), Bernt Isak Wærstad (Oslo), Øyvind Brandtsegg (San Diego), Trond Engum and Andreas Bergsland (Trondheim). Gyrid N. Kaldestad, Oslo, was also invited but unable to participate.

The meeting revolves around the issues “mixing and timbral character” as related to the crossadaptive project. As there are many aspects of the project that touches upon these issues, we have kept the agenda quite open as of yet, but asking each participant to bring one problem/question/issue.

Mixing, masking

In Oslo they worked with the analysis parameters spectral crest and flux, aiming to use these to create a spectral “ducking” effect, where the actions of one instrument could selectively affect separate frequency bands of the other instrument. Gary is also interested in these kinds of techniques for mixing, to work with masking (allowing and/or avoiding masking). One could think if it as a multiband sidechaining with dynamic bands, like a de-esser, but adaptive to whichever frequency band currently needs modification. These techniques are related both to previous work on adaptive mixing (for example at QMUL) and also partially solved by recent commecial plugins, like Izotope Neutron.
However interesting these techniques are, the main focus of our current project is more on the performative application of adaptive and crossadaptive effects. That said, it could be fruitful using these techniques, not to solve old problems, but to find new working methods in the studio as well. In the scope of the project, this kind of creative studio work can be aimed at familiarizing ourselves with the crossadaptive methods in a controlled and repeatable setting. Bernt also brought up the issue of recording the analysis signals, using them perhaps as source material for creative automation, editing the recorded automation as one might see fit. This could be an effective way of familiarization with the analyzer output as well, as it invites taking a closer look at the details of the output of the different analysis methods. Recording the automation data is straightforward in any DAW, since the analyzer output comes into the DAW as external MIDI or OSC data. The project does not need to develop any custom tools to allow recording and editing of these signals, but it might be a very useful path of exploration in terms of working methods. I’d say yes please, go for it.

Working with composed material, post production

Trond had recently done a crossadaptive session with classical musicians, playing composed material. It seems that this, even though done “live” has much in common with applying crossadaptive techniques in post production or in mixing. This is because the interactive element is much less apparent. The composition is a set piece, so any changes to the instrumental timbre will not change what is played, but rather can influence the nuances of interpretation. Thus, it is much more a one-way process instead of a dialectic between material and performance. Experts on interpretation of composed music will perhaps cringe at this description, saying there is indeed a dialogue between interpretation and composition. While this is true, the degree to which the performed events can be changed is lesser within a set composition. In recent sessions, Trond felt that the adaptive effects would exist in a paralell world, outside of the composition’s aesthetic, something unrelated added on top. The same can be said about using adaptive and crossadaptive techniques in a mixing stage of a production, where all tracks are previously recorded and thus in a sense can be regarded as a set (non-changeable) source. With regards to applying analysis and modulation to recorded material, one could also mention that the Oslo sessions used recordings of the (instruments in the session) to explore the analysis dimensions. This was done as an initial exploratory phase of the session. The aim was finding features that already exist in the performer’s output, rather than imposing new dimensions of expression that the performer will need to adapt to.

On repeatability and pushing the system

The analysis-modulator response to an acoustic input is not always explicitly controllable. This is due to the nature of some of the analysis methods, technical weaknesses that introduce “flicker” or noise in the analyzer output. Even though these deviations are not inherently random, they are complex and sometimes chaotic. In spite of these technical weaknesses, we notice that our performers often will thrive. Musicians will often “go with the flow” and create on the spot, the interplay being energized by small surprises and tensions, both in the material and in the interactions. This will sometimes allow the use of analysis dimensions/methods that have spurious noise/flicker, still resulting in a consistent and coherent musical output, due to the performer’s experience in responding to a rich environment of sometimes contradicting signals. This touches one of the core aspects of our project, intervention into the traditional modes of interplay and musical communication. It also touches upon the transparency of the technology, how much should the performer be aware of the details of the signal chain? Sometimes rationalization makes us play safe. A fruitful scenario would be aiming for analysis-modulator mappings that create tension, something that intentionally disturbs and refreshes. The current status of our research leaves us with a seemingly unlimited amount of combinations and mappings, a rich field of possibilities, yet to be charted. The options are still so many that any attempt at conclusions about how it works or how to use it seems futile. Exploration in many directions is needed. This is not aimless exploration, but rather searching without knowing what can be found.

Listening, observing

Andreas mentions is is hard to pinpoint single issues in this rich field. As observer it can be hard to decode what is happening in the live setting. During sessions, it is sometimes a complex task following the exact details of the analysis and modulation. Then, when listening to the recorded tracks again later, it is easier to appreciate the musicality of the output. Perhaps not all details of the signal chain are cleanly defined and stringent in all aspects, but the resulting human interaction creates a lively musical output. As with other kinds of music making, it is easy to get caught up in detail at time of creation. Trying to listen more in a holistic manner, taking in the combined result, is a skill not to be forgotten also in our explorations.

Adaptive vs cross-adaptive

One way of working towards a better understanding of the signal interactions involved in our analyzer-modulator system is to do adaptive modulation rather than cross-adaptive. This brings a much more immediate mode of control to the performer, exploring how the extracted features can be utilized to change his or her own sound. It seems several of us have been eager to explore these techniques, but putting it off since it did not align with the primary stated goals of crossadaptivity and interaction. Now, looking at the complexity of the full crossadaptive situation, it is fair to say that exploration of adaptive techniques can serve as a very valid manner of getting in touch with the musical potential of feature-based modulation of any signal. In it’s own right, it can also be a powerful method of sonic control for a single performer, as an alternative to a large array of physical controllers (pedals, faders, switches). As mentioned earlier in this session, working with composed material or set mixes can be a challenge to the crossadaptive methods. Exploring adaptive techniques might be more fruitful in those settings. Working with adaptive effects also brings the attention to other possibilities of control for a single musician over his or her own sound. Some of the recent explorations of convolution with Jordan Morton shows the use of voice controlled crossadaptivity as applied to a musician’s own sound. In this case, the dual instrument of voice and bass operated by a single performer allows similar interactions between instruments, but bypassing the interaction between different people, thus simplifying the equation somewhat. This also brings our attention to using voice as a modulator for effects for instrumentalists not using voice as part of their primary musical output. Although this has been explored by several others (e.g. Jordi Janner, Stefano Fasciani, and also the recent Madrona Labs “Virta” synth) it is a valid and interesting aspect, integral to our project.

 

Session UCSD 14. Februar 2017

Liveconvolver4_trig

Session objective

The session objective was to explore the live convolver, how it can affect our playing together and how it can be used. New convolver functionality for this session is the ability to trigger IR update via transient detection, as opposed to manual triggering or periodic metro-triggered updates. The transient triggering is intended to make the IR updating more intuitive and providing a closer interaction between the two performers. We also did some quick exploration of adaptive effects processing (not cross-adaptive, just auto-adaptive). The crossadaptive interactions can sometimes be complex. One way to familiarize ourselves with the analysis methods and the modulation mappings could be to allow musicians to explore how these are directly applied to his or her own instrument.

Kyle Motl: bass
Oeyvind Brandtsegg: convolver/singer/tech/camera

Live convolver

Several takes were done, experimenting with manual and transient triggered IR recording. Switching between the role of “recording/providing the impulse response” and of “playing through, or on, the resulting convolver”. Reflections on these two distinct performative roles were particularly friutful and to some degree surprising. Technically, the two sound sources of audio convolution are equal, it does not matter which way the convolution is done (one sound with the other, or vice versa). The output sound will be the same. However, our liveconvolver does treat the two signals slightly differently, since one is buffered and used as the IR, while the other signal is directly applied as input to the convolver. The buffering can be updated at any time, in such a fashion that no perceptible extra delay occurs due to that part of the process. Still, the update needs to be triggered somehow. Some of the difference in roles occur due to the need for (and complications of) the triggering mechanism, but perhaps the deepest difference occurs due to something else. There is a performative difference in the action of providing an impulse response for the other one to use, and the action of directly playing through the IR left by the other. Technically, the difference is minute, due to the streamlined and fast IR update. Perhaps also the sounding result will be perceptually indistinguishable for an outside listener. Still the feeling for the performer is different within those two roles.  We noted that one might naturally play different type of things, different kinds of musical gestures, in the two different roles. This inclination can be overcome by intentionally doing what would belong to the other role, but it seem the intuitive reaction to the role is different in each case.

Video: a brief glimpse into the session environment.

 

 conv1_mix

Take 1: IR recorded from vocals, with a combination of manual and transient triggering. The bass is convolved with the live vocal IR. No direct (dry) signals was recorded, only the convolver output. Later takes in the session also recorded the direct sound from each instrument, which makes it easier to identify the different contributions to the convolution. This take serves more as a starting point from where we continued working.

 

 conv2_mix

Take 2: Switched roles, so IR is now recorded from the bass, and the vocals are convolved with this live updated IR. The IR updates were triggered by transient detection of the bass signal.

 

 conv3_mix

Take 3: As  for take 2, the IR is recorded from bass. Changed bass mic to try to reduce feedback, adjusted transient triggering parameters so that IR recording would be more responsive

 

Video: Reflections on IR recording, on the roles of providing the IR as opposed to being convolved by it.

Kyle noticed that he would play different things when recording IR than when playing through an IR recorded by the vocals. Recording an IR, he would play more percussive impulses, and for playing through the IR he would explore the timbre with more sustained sounds. In part, this might be an effect of the transient triggering, as he would have to play a transient to start the recording. Because of this we also did one recording of manually triggered IR recording with Kyle intentionally exploring more sustained sounds as source for the IR recording. This seems to even out the difference (between recording IR and playing through it) somewhat, but there is still a performatively different feeling between the two modes.
When having the role of “IR recorder/provider”, one can be very active and continuously replace the IR, or leave it “as is” for a while, letting the other musician explore the potential in this current IR. Being more active and continuously replacing the IR allows for a closer musical interaction, responding quickly to each other. Still, the IR is segmented in time, so the “IR provider” can only leave bits and pieces for the other musician to use, while the other musician can directly project his sounds through the impulse responses left by the provider.

 

 conv4_mix

Take 4:IR is recorded from bass. Manual triggering of the IR recording (controlled by a button), to explore the use of more sustained impulse responses.

 

Video: Reflections on manually triggering the IR update, and on the specifics of transient triggered updates.

 

 conv5_mix

Take 5: Switching roles again, so that the IR is now provided by the vocals and the bass is convolved. Transient triggered IR updates, so every time a vocal utterance starts, the IR is updated. Towards the end of the take, the potential for faster interaction is briefly explored.

 

Video: Reflections on vocal IR recording and on the last take.

Convolution sound quality issues

The nature of convolution will sometimes create a muddy sounding audio output. The process will dampen high frequency content and emphasize lower frequencis. Areas of spectral overlap between two two signals will also be emphasized, and this can create a somewhat imbalanced output spectrum. As the temporal features of both sounds are also “smeared” by the other sound, this additionally contributes to the potential for a cloudy mush. It is welll known that brightening the input sounds prior to convolution can alleviate some of these problems. Further refinements have been done recently by Donahue, Erbe and Puckette in the ICMC paper “Extended Convolution Techniques for Cross-Synthesis”. Although some of the proposed techniques does not allow realtime processing, the broader ideas can most certainly be adapted. We will explore this further potential for refinement of our convolver technique.

As can be heard in the recordings from this session, there is also a significant feedback potential when using convolution in a live environment and the IR is sampled in the same room as it is directly applied. The recordings were made with both musicians listening to the convolver output over speakers in the room. If we had been using headphones, the feedback would not have been a problem, but we wanted to explore the feeling of playing with it in a real/live performance setting. Oeyvind would control simple hipass and lowpass filtering of the convolver output during performance, and thus had a rudimentary means of manually reducing feedback. Still, once unwanted resonances are captured by the convolution system, they will linger for a while in the system output. Nothing has been done to repair or reduce the feedback in these recordings, we keep it as a strong reminder that it is something that needs to be fixed in the performance setup. Possible solutions consist of exploring traditional feedback reduction techniques, but it could also be possible to do an automatic equalization based on the accumulated spectral content of the IR. This latter approach might also help output scaling and general spectral balance, since already prominent frequencies would have less poential to create strong resonances.

Adaptive processing

As a way to investigate and familiarize ourselves with the different analysis features and the modulation mappings of these signals, we tried to work on auto-adaptive processing. Here, features of the audio input affects effect processing of the same signal. The performer can then more closely interact with the effects and explore how different playing techniques are captured by the analysis methods.

 

 cut_ad_dly1

Adaptive take 1: Delay effect with spectral shift. Short (constant) delay time, like a slapback delay or comb filter. Envelope crest controls the cutoff frequency of a lowpass filter inside the delay loop. Spectral flux controls the delay feedback amount. Transient density controls a frequency shifter on the delay line output.

 

 cut_ad_rvb1

Adaptive take 2: Reverb. Rms (amplitude) controls reverb size. Transient density controls the cutoff frequency of a highpass filter applied after the reverb, so that higher density playing will remove low frequencies from the reverb. Envelope crest controls a similarly applied lowpass filter, so that more dynamic playing will remove high frequencies from the reverb.

 

 cut_ad_hadron1

Adaptive take 3: Hadron. Granular processing where the effect has its own multidimensional mapping from input controls to effect parameters. The details of the mapping is more complex. The resulting effect is that we have 4 distinctly different effect processing settings, where the X and Y axis of a 2D control surface provides a weighted interpolation between these 4 settings. Transient density controls the X axis, and envelope crest controls the Y axis. A live excerpt of the controls surface is provided in the video below.

Video of the Hadron Particle Synthesizer control surface controlled by bass transient density and envelope crest.

Some comments on analysis methods

The simple analysis parameters, like rms amplitude and transient density works well on all (most) signals. However, other analysis dimensions (e.g. spectral flux, pitch, etc) have a more inconsistent relation between signal and analysis output when used on different types of signals. They will perform well on some instrument signals and less reliably on others. Many of the current analysis signals have been developed and tuned with a vocal signal, and many of them do not work so consistently for example on a bass signal. Due to this, the auto-adaptive control (as shown in this session) is sometimes a little bit “flaky”. The auto-adaptive experiments seems a good way to discover such irregularities and inconsistencies in the analyzer output. Still, we also have a dawning realization that musicians can thrive with some “livelyness” in the control output. Some surprises and quick turns of events can provide energy and creative input for a performer. We saw this also in the Trondheim session where rhythm analysis was explored, and in the discussion of this in the follow-up seminar. There, Oeyvind stated that the output of the rhythm analyzer was not completely reliable, but the musicians stated they were happy with the kind of control it gave, and that it felt intuitive to play with. Even though the analysis sometimes fail or misinterprets what is being played, the performing musician will react to whatever the system gives. This is perhaps even more interesting (for the musician), says Kyle. It creates some sort of tension, something not entirely predictable. This unpredictability is not the same as random noise. There is a difference between something truly random and something very complex (like one could say about an analysis system that misinterprets the input). The analyzer would react the same way to an identical signal, but give unproportionally large variance in the output due to small variances in the input. Thus it is a nonlinear complex response from the analyzer. In the technical sense it is controllable and predictable, but it is very hard to attain precise and determined control on a real world signal. The variations and spurious misinterpretations creates a resistance for the performer, something that creates energy and drive.

 

 

 

Seminar 16. December

Philosophical and aesthetical perspectives

–report from meeting 16/12 Trondheim/Skype

Andreas Bergsland, Trond Engum, Tone Åse, Simon Emmerson, Øyvind Brandtsegg, Mats Claesson

The performers experiences of control:

In the last session (Trondheim December session) Tone and Carl Haakon (CH) worked with rhythmic regularity and irregularity as parameters in the analysis. They worked with the same kind of analysis, and the same kind of mapping analysis to effect parameter. After first trying the opposite, they ended up with: Regularity= less effect, Irregularity= more. They also included a sample/hold/freeze effect in one of the exercises. Øyvind commented on how Tone in the video stated that she thought it would be hard to play with so little control, but that she experienced that they worked intuitively with this parameter, which he found was an interesting contradiction. Tone also expressed in the video that on the one side she would sometimes hope for some specific musical choices from CH (“I hope he understands”) but on the other hand that she “enjoyed the surprises”. These observations became a springboard for a conversation about a core issue in the project: the relationship between control and surprise, or between controlling and being controlled. We try to point here to the degree of specific and conscious intentional control, as opposed to “what just happens” due to technological, systemic, or accidental reasons.  The experience from the Trondheim December session was that the musicians preferred what they experienced as an intuitive connection between input and outcome, and that this facilitated the process in the way that they could “act musically”. (This “intuitive connection” is easily related to Simon’s comment about “making ecological sense” later in this discussion.)  Mats commented that in the first Oslo session the performers stated that they felt a similarity to playing with an acoustic instrument. He wondered if this experience had to do with the musicians’ involvement in the system setup, while Trond pointed out that the Trondheim December session and Oslo session were pretty similar in this respect. A further discussion about what “control”, “alienation” and “intuitive playing” can mean in these situations seems appropriate.

Aesthetic and individual variables

This led to a further discussion about how we should be aware that the need for generalising and categorising – which is necessary at some point to actually be able to discuss matters – can lead us to overlook important variable parameters such as:

  • Each performer’s background, skills, working methods, aesthetics and preferences
  • That styles and genres relate differently to this interplay

A good example of this is Maja’s statement in the Brak/Rug session that she preferred the surprising, disturbing effects, which gave her new energy and ideas. Tone noted that this is very easy to understand when you have heard Maja’s music, and even easier if you know her as an artist and person. And it can be looked upon as a contrast to Tone/CH who seek a more “natural” connection between action and sounding result, in principle they want the technology to enhance what they are already doing. But, as cited above, Tone commented that this is not the whole truth. Surprises are also welcome in the Tone/Carl Haakon collaboration.

Simon underlined, because of these variables, the need to pin down in each session what actually happens, and not necessarily set up dialectical pairs. Øyvind pointed out, on the other hand, the need to lay out possible extremes and oppositions to create some dimensions (and terms) along which language can be used to reflect on the matters at hand.

Analysing or experiencing?

Another individual variable, both as audience and performer, is the need to analyse, to understand what is happening in the perceiving of a performance. One example brought up related to this was Andreas’ experience of his change of audience perspective after he studied ear training. This new knowledge led him to take an analysing perspective, wanting to know what happened in a composition when performed. He also said: “as an audience you want to know things, you analyse”. Simon referred to “the inner game of tennis” as another example: how it is possible to stop appreciating playing tennis because you become too occupied analysing the game – thinking of the previous shot rather than clearing the mind ready for the next. Tone pointed at the individual differences between performers, even within the same genre (like harmonic jazz improvisation) – some are very analytic, also in the moment of performing, while others are not. This also goes for the various groups of audiences, some are analytic, some are not – and there is also most likely a continuum between the analytic and the intuitive musician/audience.  Øyvind mentioned experiences from presenting the crossadaptive project to several audiences over the last few months. One of the issues he would usually present is that it can be hard for the audience to follow the crossadaptive transformations, since it is an unfamiliar mode of musical (ex)change.  However, responses to some of the simpler examples he then played (e.g. amplitude controlling reverb size and delay feedback), yielded the response that it was not hard to follow. One of the places where this happened was Santa Barbara, where Curtis Roads commented he thought it quite simple and straightforward to follow. Then again, in the following discussion, Roads also conceded that it was simple because the mapping between analysis parameter and modulated effect was known. Most likely it would be much harder to deduce what the connection was just by listening alone, since the connection (mapping) can be anything. Cross Adaptive processing may be a complicated situation, not easy to analyse either for the audience or the performer. Øyvind pointed towards differences in parameters, as we had also discussed collectively: That some were more “natural” than others, like the balance between amplitude and effect, while some are more abstract, like the balance between noise and tone, or regular/irregular rhythms.

Making ecological sense/playing with expectations

Simon pointed out that we have a long history of connections to sound: some connections are musically intuitive because we have used them perhaps for thousands of years, they make ‘ecological’ sense to us. He referred to Eric Clarke’s “ Ways of listening: An ecological approach to the perception of musical meaning (2005)” and William Gaver “What in the world do we hear?: An ecological approach to auditory event perception” (1993). We come with expectations towards the world, and one way of making art is playing with those expectations. In modernist thinking there is a tendency to think of all musical parameters as equal – or at least equally organised – which may easily undermine their “ecological validity” – although that need not stop the creation of ‘good music’ in creative hands.

Complexity and connections

So, if the need for conscious analysis and understanding will vary between musicians, is this the same for the experienced connection between input and output? And what about the difference between playing and listening as part of the process, or just listening, either as a musician, musicologist, or an audience member? For Tone and Carl Haakon it seemed like a shared experience that playing with regularity/non- regularity felt intuitive for both – while this was actually hard for Øyvind to believe, because he knew the current weakness in how he had implemented the analysis. Parts of the rhythmic analysis methods implemented are very noisy, meaning they produce results that sometimes can have significant (even huge) errors in relation to a human interpretation of the rhythms being analysed. The fact that the musicians still experienced the analyses as responding intuitively is interesting, and it could be connected to something Mats said later on: “the musicians listen in another way, because they have a direct contact with what is really happening”. So, perhaps, while Tone &CH experienced that some things really made musical sense, Øyvind focused on what didn’t work – which would be easier for him to hear?  So how do we understand this, and how is the analysis connected to the sounding result? Andreas pointed out that there is a difference between hearing and analysing: you can learn how the sound behaves and work with that. It might still be difficult to predict exactly what will happen.Tone’s comment here was that you can relate to a certain unpredictability and still have a sort of control over some larger “groups of possible sound results“ that you can relate to as a musician. There is not only an urge to “make sense” (= to understand and “know” the connection) but also an urge to make “aesthetical sense”.

With regards to the experienced complexity, Øyvind also commented that the analysis of a real musical signal is in many ways a gross simplification, and by trying to make sense of the simplification we might actually experience it as more complex. The natural multidimensionality of the experienced sound is lost, due to the singular focus on one extracted feature. We are reinterpreting the sound as something simpler. An example mentioned was the vibrato, which is a complex input and a complex analysis, that could in some analyses be reduced to a simple “more or less” dimension. This issue also relates to the needs of our project to construct new methods of analysis, so that we can try to find analysis dimensions that correspond to some perceptual or experiential features.

Andreas commented “It is quite difficult to really know what is going on without having knowledge of the system and the processes. Even simple mappings can be difficult to grasp only by ear”. Trond reminded us after the meeting about the further complexity that was perhaps not so present in our discussion: we do not improvise with only one parameter “out of control” (adaptive processing). In the cross adaptive situation someone else is processing our own instrument, so we do not have full control over this output, and at the same time we do not have any control over what we are processing, the input (cross- adapting), which in both cases could represent an alienation and perhaps a disconnection from the input-result- relation. And of course the experience of control is also connected to “understanding” the processing analysis you are working with.

The process of interplay:

Øyvind referred to Tone’s experience of a musical “need” during the Trondheim session, expressed: ”I hope he understands…” –  when she talked about the processes in the interplay. This was pointing at how you realise during the interplay that you have very clear musical expectations and wishes towards the other performer.  This is not in principle different from a lot of other musical improvising situations. Still, because you are dependent on the other’s response in a way that is defining not only the wholeness, but your own part in it, this thought seemed to be more present than is usual in this type of interplay.

Tools and setup

Mats commented that very many of the effects that are used are about room size, and that he felt that this had some – to him – unwanted aesthetical consequences. Øyvind responded that he wanted to start with effects that are easy to control and easy to hear the control of. Delay feedback and reverb size are such effects. Mats also suggested that it was an important aesthetical choice not to have effects all the time, and thereby have the possibility to hear the instrument itself. So to what extent should you be able to choose? We discussed the practical possibilities here: some of the musicians (for example Bjørnar Habbestad) have suggested a foot pedal,  where the musician could control the degree to which their actions will inflict changes on the other musician’s sound (or the other way around, control the degree to which other forces can affect his sound). Trond suggested one could also have control over the level of signal/output  for the effects, adjusting the balance between processed and unprocessed sound. As Øyvind commented, these types of control could be a pedagogical tool for rehearsing with the effect, turning the processing on and off to understand the mapping better. The tools are of course partly defining the musician’s balance between control, predictability and alienation. Connected to this, we had a short discussion regarding amplified sound in general, that the instrumental sound coming from a speaker located elsewhere in the room in itself could already represent an alienation. Simon referred to the Lawrence Casserley /Evan Parker principle of “each performer’s own processor”, and the situation before the age of the big PA, where the electronic sound could be localised to each musician’s individual output. We discussed possibilities and difficulties with this in a cross adaptive setting: which signal should come out of your speaker? The processed sound of the other, or the result of the other processing you? Or both? and then what would the function be – the placement of the sound is already disturbed.

Rhythm

New in this session was the use of the rhythmical analysis. This is very different from all other parameters we have implemented so far. Other analyses relate to the immediate sonic character, but rhythmic analysis tries to extract some  temporal features, patterns and behaviours. Since much of the music played in this project is not based on a steady pulse, and even less confined to a regular grid (meter), the traditional methods of rhythmic analysis will not be appropriate. Traditionally one will find the basic pulse, then deduce some form of meter based on the activity, and after this is done one can relate further activity to this pulse and meter. In our rhythmical analysis methods we have tried to avoid the need to first determine pulse and meter, but rather looked into the immediate time relationships between neighbouring events. This creates much less support for any hypothesis the analyser might have about the rhythmical activity, but also allows much greater freedom of variation (stylistically, musically) in the input. Øyvind is really not satisfied with the current status of the rhythmic analysis (even if he is the one mainly responsible for the design), but he was eager to hear how it worked when used by Tone and Carl Haakon.  It seems that the live use by real musicians allowed the weaknesses of the analyses to be somewhat covered up. The musicians reported that they felt the system responded quite well (and predictably) to their playing. This indicates that, even if refinements are much needed, the current approach is probably a useful one. One thing that we can say for sure is that some sort of rhythmical analysis is an interesting area of further exploration, and that it can encode some perceptual and experiential features of the musical signal in ways that make sense to the performers. And if it makes sense to the performers, we might guess that it will have the possibility of making sense to the listener as well.

Andreas: How do you define regularity (ex. claves-based musics), how “less regular” is that from a steady beat.

Simon: If you ask a difficult question with a range of possible answers this will be difficult to implement within the project.

As a follow up to the refinement of rhythmic analysis, Øyvind asked:  how would *you* analyze rhythm?

Simon: I wouldn’t analyze rhythm for example timeline in African music: a guiding pulse that is not necessarily performed and may exist only in the performer’s head. (This relates directly to Andreas’s next point – Simon later withdrew the idea that he would not analyse rhythm and acknowledged its usefulness in performance practice.)

Andreas: Rhythm is a very complex phenomenon, which involves multiple interconnected temporal levels, often hierarchically organised. Perceptually, we have many ongoing processes involving present, past and anticipations about future events. It might be difficult to emulate such processes in software analysis. Perhaps pattern recognition algorithms can be good for analysing rhythmical features?

Mats: what is rhythm? In our examples: gesture may be more useful than rhythm

Øyvind: rhythm is repeatability, perhaps? Maybe we interpret this in the second after

Simon: no I think we interpret virtually at the same time

Tone: I think of it as a bodily experience first and foremost.  (Thinking about this in retrospect, Tone adds: The impulses -when they are experienced as related to each other- creates a movement in the body. I register that through the years (working with non-metric rhythms in free improvisation) there is less need for a periodical set of impulses to start this movement. (But when I look at babies and toddlers, I recognise this bodily reaction to irregular impulses.) I recognice what Andreas says- the movement is trigged by the expectation of more to come. (Think about the difference in your body when you wait for the next impulse to come (anticipations) and when you know that it is over….)

Andreas: When you listen to rhythms, you group events on different levels and relate to what was already played. The grouping is often referred to as «chunking» (psychology). Thus, it works both on an immediate level (now) as well as a more overarching level (bar, subsection, section) because we have to relate what we hear to the earlier. You can simplify or make it complex

Seminar 21. October

We were a combination of physically present and online contributors to the seminar.  Joshua Reiss and Victor Lazzarini participated via online connection, present together in Trondheim were: Maja S.K. Ratkje, Siv Øyunn Kjenstad, Andreas Bergsand, Trond Engum, Sigurd Saue and Øyvind Brandtsegg

Instrumental extension, monitoring, bleed

We started the seminar by hearing from the musicians how it felt to perform during Wednesday’s session. Generally, Siv and Maja expressed that the analysis and modulation felt like an extension to their original instrument. There were issues raised about the listening conditions, how it can be difficult to balance the treatments with the acoustic sound. One additional issue in this respect when working cross-adaptively (as compared to e.g. the live processing setting), is that there is not a musician controlling the processing, to the processed sound is perhaps a little bit more “wild”. In a live processing setting, the musician controlling the processing will attempt to ensure a musically shaped phrasing and control that is at the current stage not present in the crossadaptive situation. Maja also reported acoustic bleed from the headphones to the feature extraction for her sound. With this kind of sensitivity to crosstalk, the need for source separation (as discussed earlier) is again put to our attention.  Adjusting the signal gating (noise floor threshold for the analyzer) is not sufficient in many situations, and raising the threshold also lowers the analyzer sensitivity to soft playing. Some analysis methods are more vulnerable than others, but it is safe to say that none of the analysis methods are really robust against noise or bleed from external signals.

Interaction scenarios as “assignments” for the performers

We discussed the different types of mapping (of features to modulators) which the musicians also called “assignments”, as it was experienced as a given task to perform utilizing certain expressive dimensions in specific ways to control the timbre of the other instrument. This is of course true. Maja expressed that she was most intrigued by the mappings that felt “illogical”, and that illogical was good. By illogical, she means mappings that does not feel natural or as intuitive musical energy flows. Things that break up the regular musical attention, and break up the regular flow from  idea to expression. As an example was mentioned the use of pitch to control reverberation size. For Maja (for many, perhaps for most musicians), pitch is such a prominent parameter in the shaping of a musical statement, so it is hard to play when some external process interferes with the intentional use of pitch. The linking of pitch to some timbral control is such an interference, because it creates potential conflict between the musically intended pitch trajectory and the musically intended timbral control trajectory. An interaction scenario (or in effect, a mapping from features to modulators to effects), can in some respects be viewed as a composition, in that it sets a direction for the performance. In many ways similar to the text scores of the experimental music of the 60’s, where the actual actions or events unfolding are perhaps not described, but more a description of an idea of how the musicians may approach the piece. For some, this may be termed a composition, others might use the term score. In any case it dictates or suggests some aspects of what the performers might do, and as such consists of an external  implication on the performance.

Analysis, feature extraction

Some of our analysis methods are still a bit flaky, i.e. we see spurious outliers in their output that is not necessarily caused by perceptible changes in the signal being analyzed. One example of this is the rhythm consonance feature, where we try to extract a measure of rhythmic complexity by measuring neighboring delta times between events and looking for simple ratios between these. The general idea being that simpler the ratio, the simpler the rhythm is. The errors sneak in as part of the tolerance for human deviation in rhythmic performance, where one may clearly identify one intended pattern, while the actual measured delta times can deviate more than a musical time division (for example, when playing a jazzy “swing 8ths” triplet pattern, which may be performed somewhere between equal 8th notes, a triplet pattern, or even towards a dotted 8th plus a 16th and in special cases a double dotted 8th plus a 32nd). When looking for simple integer relationships small deviations in phrasing may lead to large changes in the algorithm’s output. For example 1:1 for a straight repeating 8th pattern, 2:1 for a triplet pattern and 3:1 for a dotted 8th plus 16th pattern, re the jazz swing 8ths. See also this earlier post for more details if needed.  As an extreme example, think of a whole note at a slow tempo (1:1) versus an accent on the last 16th note on a measure (giving a 15:16 ratio). These deviations create single values with a high error. Some common ways of dampening the effect of such errors would be lowpass filtering, exponential moving average, or median filtering. One problem in the case of rhythmic analysis is that we only get new values for each new event, so the “sampling rate” is variable and also very low. This means that any filtering has the consequence of making the feature extraction respond very slowly (and also with a latency that varies with the number of events played), something that we would ideally try to avoid.

Stabilizing extraction methods

In the light of the above, we discussed possible methods for stabilizing the feature extraction methods to avoid the spurious large errors. One conceptual difficulty is differentiating between a mistake and an intended expressive deviation.  More importantly, to differentiate between different possible intended phrasings. How do we know what the intended phrasing is without embedding too many assumptions in our analysis algorithm? For rhythm, it seems we could do much better if we first deduct the pulse and the meter, but we need to determine what our (performed) phrasings are to be sure of the pulse and meter, so it turns into a chicken and egg problem. Some pulse and meter detection algorithms maintain several potential alternatives, giving each alternative a score for how well it fits in light of the observed data. This is a good approach, assuming we want to find the pulse and meter. Much of the music we will deal with in this project does not have a strong regular pulse, and it most surely does not have a stable meter. Let’s put the nitty gritty details of this aside for a moment, and just assume that we need some kind of stabilizing mechanism. As Josh put it, a restricted form of the algorithm.
Disregarding the actual technical difficulties, let’s say we want some method of learning what the musician might be up to, what is intended, what is mistake, and what are expressive deviations from the norm. Some  sort of calibration the normal, average, or regularly occurring behavior. Track change during session, and this is change relative to the norm as established in the traning. Now, assuming we could actually build such an algorithm, when should it be calibrated (put into learn mode)? Should we continuously update the norm, or just train once and for all? If training before performance (as some sort of sound check), we might fail miserably because the musician might do wildly different things in the “real” musical situation compared to when “just testing”. Also, if we continuously update the norm, then our measures are always drifting, so something that was measured as “soft” in the beginning of the performance might be indicated as something else entirely by the end of the performance. Even though we listen to musical form as a relative change, we might also as listeners recognize when “the same” happens again later. E.g. activity in the same pitch register, the same kind of rhythmic density, the same kind of staccato abrupt complex rhythms etc. with a continuously updated norm, we might classify the same as something different. Regarding the attempt to define something as the same see also the earlier post on philosophical implications. Still, with all these reservations, it seems necessary to attempt creating methods for relative change. This can perhaps be used as a restricted form, as Joshua suggests, or in any case as an interesting variation on the extracted features we already have.  It would extend the feature output formats of absolute value, dynamic range, crest. In some ways it is related to dynamic range (f.ex. as the relative change would to some degree be high when the dynamic range is high, but then again the relative change would have a more slowly moving reference, and it would also be able to go negative). As a reference for the relative change, we could use a long time average, a model of expectation, assumption of the current estimate (maintaining several candidates as with pulse and meter induction), or normal distribution and standard deviation. These long term estimates have been used with success in A-DAFx (adaptive audio effects) for live applications.

Josh mentioned the possibility of doing A/B comparision of the extraction methods with some tests at QMUL. We’ll discuss this further.

Display of extracted features

When learning (an instrument), multimodal feedback can significantly reduce the time taken to gain proficiency. When learning how the different feature extraction methods work, and how they react to intentional expressive changes in the signal, visual feedback might be useful. Other means of feedback could be sonifying the analysis (which is what we do already, but perhaps make it more pointed and simple. This could be especially useful when working with the gate mix method, as the gate will give not indication to the performer that it will soon open, whereas a sonification of the signal could aid the performer in learning the range of the feature and getting an intuitive feel for when the gate will open. Yet another means of feedback is giving the performer the ability to adjust the scaling of the feature-to-modulator mapping. In this way, it would act somewhat like giving the performer that ability to tune the instrument, ensuring that it reacts dynamically to the ranges of expression utilized by this performer. Though not strictly a feedback technique, we could still treat it as a kind of familiarization aid in that it acts as a two-way process between performer and instrument. The visualization and the performer adjustable controls could be implemented as a small GUI component running on portable devices like cellphone or touchpad. The signals can be communicated from the analyzer and MIDIator via OSC, and the selection of features to display can be controlled by the assignments of features in the MIDIator. A minimal set of controls can be exposed, and the effects of these being mirrored in the plugins (MIDIator). Some musicians may prefer not to have such a visual feedback. Siv voiced concern that she would not be so interested in focusing visually on the signals. This is a very valid concern for performance. Let us assume it will not be used during actual performance, but as a tool for familiarization during early stages of practice with the instrument.