While emulations of other classic analogue synths abound, there's only ever been one way to get your hands on a CS80 — until now.
Over the past few years we've been inundated with wonderful recreations of venerable analogue synthesizers: the Minimoog, the ARP Odyssey, the Korg MS20, the Oberheim SEM and, with an extra voice, the Prophet 5. Nonetheless, fans of the Yamaha CS series (whether monophonic or polyphonic) have been poorly served up to this point. In fact, they haven't been served at all. Until now.
A remarkably sophisticated synthesizer for its era, the CS80 was based upon two independent eight-voice, VCO/VCF/VCA synthesizers represented by a single row of controls that Yamaha called 'Channels' or, individually, Synth I and Synth II, and which Black Corporation calls Layer I and Layer II. A third row of faders and a panel alongside the keyboard then controlled tuning, modulation, and performance parameters. A quick visual inspection shows that, with a handful of significant omissions, Deckard's Dream recreates this architecture with remarkable accuracy, so seasoned CS80 aficionados should feel at home with it.
I was keen to compare the two instruments, so I placed Deckard's Dream alongside my CS80 and started with an evaluation of their oscillators. On Deckard's Dream these are based upon the recently recreated CEM3340 oscillators from On Chip. As on the original synth, they produce sawtooth, pulse and sine waves, the first two of which pass through the filter section while the third is injected directly into the first of the VCAs that follow the filter section.
I began by comparing their sawtooth waves and found them to be all but identical. The square waves on my CS80 were a touch brighter than those of Deckard's Dream but this was a consequence of 42 years of drift; the two instruments sounded alike after I tweaked the pulse width on the CS80. Turning to the pulse-width modulation (PWM) I found that the slowest sweep on my CS80 was slower than the slowest setting on Deckard's Dream, and the fastest setting on Deckard's Dream was faster than the fastest on the CS80. However, when I turned to the Settings menus in Deckard's Dream I found all manner of 'per-patch' parameters, some of which allowed me to adjust the time constants of various functions. In this case, I was able to reduce the minimum PWM rate from around 0.7Hz to 0.1Hz, and increase the maximum from around 70Hz to 100Hz. Nonetheless, the maximum PWM depth was still greater on the CS80, and there was no way to make Deckard's Dream equal this. Perhaps by way of recompense, you can choose between two global PWM modes: Separate, in which the PWM rates of Layer I and Layer II are independent of one another, and Sync, in which they're not.
Turning to the sine wave, I found that I could obtain a higher maximum level for this on the CS80, especially at low frequencies. But perhaps the greatest difference between the raw sound sources of the two instruments lies in their noise generators. On the CS80, the noise has a high maximum amplitude and significant low-frequency content while, on Deckard's Dream, it's far whiter and has much lower amplitude. This means that patches based upon noise or which mix cyclic waveforms with noise may not sound the same on the two instruments.
The CS80 offers a pair of filters for each voice, a 12dB/oct resonant (but not self‑oscillating) high-pass filter and a 12dB/oct resonant (but not self-oscillating) low-pass filter. Comparing Deckard's Dream to the CS80, I have to admit to being impressed with its LPFs; not only do they open and close to the same degree, they do so with the same timbral effect at all resonance levels. The sound of the high-pass filters is less similar to the original's, with the CS80's having a more pronounced effect on the sound, but I'm not complaining. When you see what Scott Rider had to do to reverse-engineer and recreate these circuits (see http://synthtech.com/motm/480/) you'll stand in awe of his expertise.
The cutoff frequencies of both filters in a given Layer in Deckard's Dream are affected by a digitally generated four-stage contour. This is described in different places in the manual as an ADR and as an ADSR envelope generator, but in both cases that's wrong. As on the CS80, it's described by five controls: the Initial Level...
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