final performance: technical details

The performance I presented as the final project involves an audio/visual instrument composed of a few different systems.

Audio

The audio processes are essentially embodied by a Max (Cycling’74) patch. It is a rather complex system and makes use of many non native objects as well as one proprietary process (a compressor) so I invite who is interested in having it to contact me at my e-mail address to have instructions.

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The first sound heard through the piece is the signal of a microphone attached to a wooden box; the signal is then processed by two sets of eight resonant filter banks, each featuring eleven filters and each being independent from one another (they can keep ringing while other ones are excited). Let us consider the first set: each bank has fixed gains for each filter and a fixed fundamental frequency assigned to the first one, but this first filter has a very low gain, so that it is hard to perceive it compared to the others. The remaining ten filters have variable frequencies that are most of the time aliased beyond the Nyquist frequency and thus symmetrically reflecting within the audible spectrum, contributing to make the fundamental frequency of each bank imperceptible and to achieve a general timbral complexity. The current active bank is selected after each attack exceeding a value of 2.5 % of the full digital scale, while frequencies are shifted after a certain number of these attacks; this number is controlled by the height of the performer’s left shoulder. The second set works in a slightly different way: here the fundamental frequency of each bank is more audible, is lower and there isn’t aliasing, so that the final result is more similar to standard modal processes; however, fundamental frequencies across the banks are more spread out (55 to 220 Hz), so variety is preserved. Current bank is selected after each attack exceeding a value of 2.0 % of the full digital scale and frequencies are always moving in accordance to a random signal, whose rate and scale though is controlled by the height of the performer’s left shoulder. For both sets, the Q factor of the filters is scaled depending on their index (the higher the index, the higher the Q, but because of the aliasing higher index does not mean higher frequency) and globally multiplied by the value of the height of the performer’s shoulder. Lastly, the bank selection is not abrupt, but happens via a smooth routing with a ramp time of 5 milliseconds: this feature had to be introduced to deal with more continuous signal coming from the microphone; for similar reasons, a V-shaped envelope of a total time of 10 milliseconds multiplies the audio input so that, when frequencies of the first bank are shifted, its level is zero.

A second, slightly less “natural” voice is a live granulation of the reverberation – incidentally, a signal driven, attack responsive one: in turns, an ever-changing space – of the first voice. Even if it is controlled by the right shoulder of the performer, its sonic nature is more abstract and the gestures much less “organic”, providing most of the times crescendos which culminate with evenly-spaced short grains.
A third voice is the feedback system which can be heard towards the end of the first section of the performance.

Interface

As mentioned above, many parameters are controlled by the movement of the performer’s shoulders. This is done using a pair of stretch sensors (available here: www.adafruit.com/products/519) attached to my pants:

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the other end of the electrical cable is then connected to a voltage divider circuit connected to an Arduino board, as well explained I this tutorial: learn.adafruit.com/thermistor/using-a-thermistor.

The Max patch I used to interface Arduino is available here: playground.arduino.cc/uploads/Interfacing/Arduino2Max_Nov2012.zip.

I found this solution very effective compared to other body motion tracking systems, first of all because they can cost thousands of pounds and secondly because it naturally provides a physical feedback of the stretching force.

Visuals

I worked on a set of four televisions fed with audio signal (scaled up 10000 times) to make them flicker. In most cases I did it using their SCART plug:

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to do that I soldered some odd cables with a TRS jack on one end and a SCART plug on the other:

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Here’s a video of a test:

For previous experiments, some of which ended up with nice videos, see my blog: https://dmsp.digital.eca.ed.ac.uk/blog/ave2014/category/blogs/marcosblog/

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