....ACOUSTIC MODELLING.... with a modular analog synthesiser.

Intro...

This part of the site describes a series of interesting simple experiments I did, in the early eighties, aimed at modelling the acoustics of a variety of real instruments electronically using an extended modular analog synthesiser. See the synthesiser adventures section for pictures etc.. I hoped to generate electronic sounds that sounded just like REAL instruments and then just play around with these models to see what could be done. At that time, in the digital world, the modelling of the acoustics of real instruments using large programs running on big mainframe computers had just begun. Nice, if you had access to these expensive esoteric machines but I didn’t. However, I reckoned, all I needed to do it analog style was to design some special analogue delay line modules to add to my existing instrument. Crazy idea?
Maybe, but it turned out to be very successful. In fact I managed to produce a wide variety of simple real sounding instrument models before anyone else did. The results created a huge amount of interest at the time and what follows is a web friendly version of a presentation/demonstration on it that I gave at the International Computer Music Conference at Cologne in 1988.
[If you would like to read the original transcript, here’s an Adobe pdf version... ICMC1988.PDF ]. 204KB


SOUND EXAMPLES...
The audio results, of course, are the proof it all worked and they are included here in the form of several short streaming audio MP3 examples. Although the sound quality of low-bit rate streaming MP3 is not good, I still think you will be surprised by what can be done on a old analog modular synthesiser.


.................DIGITAL RE-CREATIONS with free DOWNLOADS ................

As it was over twenty years ago when I did these experiments, I thought it would be a good idea to ‘celebrate’ if that’s the right word, by attempting to re-create digital versions of these patches as zip files for free download. If you have either Tassman 4 or Native Instrument’s Reaktor, you can now try them out for yourself. For historical reasons, I’m keeping them simple and as close to the originals as possible. I have to say I struggled with Tassman. Although it’s a fine program, it’s direction is quite different than mine was at the time, but I did get most of the the basic sounds to work in a fashion but on a very limited range of notes. Fortunately I fared much better with Reaktor. Its basic ‘nuts and bolts’ approach gave me the opportunity to construct basic macros very close to some of my modules like the key delay line below and my VCAs. These patches mimic my original models quite closely and super-cleanly. If you’re able to, I hope you enjoy trying them out!

TASSMAN 4 patches *.txf files; All zipped files here in one 48KB download.


NATIVE INSTRUMENTS REAKTOR 4 patches *.ens files; Zipped download files in groups:-

Strings zip (36KB), Gongs zip (61KB), Brass zip (17KB), Wind zip (36KB).,






MODEL BUILDING BLOCKS.

I’ve used block diagrams to represent standard synthesiser functions; modulators, filters, envelope shapers etc.: all familiar stuff to anyone who has ever programmed a sound synthesiser. There is however, a vital new ingredient; special audio delay line module. My signal flow design for this is shown above.

SPECIAL DELAY LINE MODULE...

It's really a voltage controlled analogue delay line with an output filter and a feedback loop. It works like this... The input signal is sampled at high frequency and the analog samples are stored in and stepped through a series of capacitive storage elements contained in a chip called a bucket brigade or charge coupled device (CCD). The quicker it gets stepped through the shorter the delay. A high frequency voltage controlled oscillator generates the stepping commands and the oscillator has a very accurate linear frequency /voltage relationship. My whole modular synthesiser’s voltage control system is linear, like Don Buchla’s was by the way. Remember him?
To ths basic delay function you can see added, a two input mixer on the front, a built in soft limiting device (to gently limit the signal amplitude before it clips) and a variable first order low pass filter (6dB/oct). On the output (not shown) is an optional output signal inverter switch, which is given special mention in the text.. More of this later. Also not shown for clarity are the necessary steep anti-aliasing filters on the input and output of the delay line chip.

CVP MODULE...

The other slightly unusual module I have is a CVP. It stands for Control Voltage Processor. It’s really a modified standard VCA (voltage controlled amplifier). However in the CVP, with zero control voltage on the contol input, the gain is unity, so it goes through unaltered. A negative control voltage reduces the gain and a positive control voltage increases the gain. The single control knob adjusts the attenuation on the control signal. A course/fine switch gives the option of greatly reduced attenuation range This makes setting of fine vibrato etc. Much easier.

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