Building David's Garden

in Blog

9 April 2006

Prototyping real-time signal processing networks in Logic.

I’m currently trying to find the best set of tools to build the David’s Garden project. The emphasis here should be on experimentation and not simply scientific construction, which the obvious software of choice – MaxMSP – promotes. Are there any other software packages already available which offers some pre-built synths and processors, whilst at the same time allowing flexibility (ie the ability to automate just about any paramter, and switch between different modules/plugins)? I might tryout Jade and Jamoma another time.

I think the answer is no. It is inevitable that due to it’s portability and availability, MaxMSP will be used. But in order to experiment a little, I will prototype some ideas in Logic first. Logic, whilst not designed for this kind of live processing, does allow quite a lot of signal routing options, thanks to it’s Environment.

The first idea I wanted to try was a granular pitch-shifter fed back into itself creating a kind of upwards glissando effect which I would then put through a spectral spacialiser, high frequencies at the back of the concert hall, lower at the front/stage. This, I hope, would create the effect that the more abstract frequencies occur far away from the real instrument whilst common frequencies (ie simply amplification) occurs only at the front of the hall. The level of abstraction in the processing and physical space are parameters which I believe should corrolate in an intuitive way.

Due to the lack of a ‘fed-back granular pitch-shifter’ plugin in Logic, I had to try and fake the effect. I set up four audio busses, each with a delay (with feedback) followed by Logic’s generic pitch-shifter (Apple’s pitch shifter sounds great but is very CPU intensive). I experimented with different levels of pitch-shifting, and found that grouping larger delay times (with higher levels of feedback) with higher pitch-shifting was quite effective.

For this to not sound too chaotic, the live input needs to be fairly sparce. For the David’s Garden project, I think it might be a good idea to map the slide position (flexion sensor on the right elbow) to the input signal attenuation parameter. Then, when David plays, for example, in third position and above, the signal gets sent to the bank of pitch shifters. This would create a very interesting visual cue – as David’s slide gets ‘longer’, the live sound gets transformed and gradually ‘evaporates’ to the back of the hall (thanks to the varing delay times).

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