The new unit, pictured above (left case),contained all the extra things I needed. Most important are the resonating electronic analogue delay lines modules based around what are generally called charged coupled devices or CCDs. With these the input signal is sampled, as it is in the digital world, but with the samples remaining as analogue electrical charges which are passed along a long string of tiny charge storage capacitors until the samples emerge at the other end. When the output is fed back to the input in various ways you create a resonator with very acoustic properties. I really struggled for some time to get the circuits right but got there in the end.
Because acoustic modelling uses the excitation and interaction of electronic devices to specifically mimic the physics of the real world this synthesis method produces some remarkably acoustic sounding instruments as opposed to electronic sounding ones. I discovered many simple models for plucked strings, gongs and bells, trumpet, saxophone and clarinet, flute and many other strange hybrid instruments. A full description of all this in the “Acoustic Modelling” section.
Today acoustic modelling is common. It has been exploited on several commercial synthesiser designs and there are also modern software applications that use it too. I’ve even reproduced some of my early patches in Native Instruments “Reaktor” (a pure software digital kit of audio parts) and included them for free download on the site.
Over the following years I gradually added extra modules until the case (pictured left) was full. This is how it stands today. Along the top row (L-R) are... 2 LFOs, 1 dual envelope shaper, 2 dual voltage controlled delay line resonators, 1 dual envelope generator, 1 dual VCA, 1 dual envelope generator and 1 dual VCA. Along the middle panel are input/output lines to sockets on the back, computer control lines, common jacks, noise and +5 volt sources. Along the bottom panel (L-R) are 1 special dual control voltage VCA module, 1 quad VCF module with LP and BP filter functions, 1 quad voltage controlled mid range delay line resonators, 1 dual multiplier/divider module and 1 3 x 3 mixer.
Sitting on top of it (top left) is an 8 x 4 analogue sequencer with internal VCO. Made around 1978, it’s based on a ring counter circuit. Each column step can be switched in or out, or the sequence looped back at various steps. An output selector can turn it onto 2 x 16 or 1 x 32 steps as well as the 8 x 4.