While setting up my CS-80, I took a number of photos to details the various controls. Click on any image to enlarge.
The above image shows the keyboard sustain and effects controls on the platform to the right of the keyboard. The key release sustain (not sustain in the envelope generator sense) and glissando/portamento can be enabled to operate on demand from the footswitch, otherwise they are enabled on the panel all the time with the white rate slider's 'short' position effectively being off. The glissando effect at slower (long) rates is rather striking; Giorgio Moroder used the distinct sound of CS-80 glissando in his film score for Cat People. Sustain mode II will cut off the release of any sounding notes not currently held down, with sustain mode I being the normal release mode.
The tremolo and chorus effects are engaged by the organ-type switch tablets shown, and the effect rate and depth by the indicated knobs. The chorusing unit is the vintage analog BBD-type, using a Panasonic MN3005 as the core circuit. Also, the exp/exp wah selectors determine how an externally-connected volume pedal will affect the sound. In the EXP position it is a simple swell pedal, but in the WAH position a voltage-controlled bandpass filter is enabled to attain the electric guitar-like wah-wah sound.
The master pitch (synthesizer sections I & II) and detune (section II) controls are located on the left end of the main panel. The master pitch control is actually two concentric knobs, one for coarse and one for fine tuning. The detune control will raise or lower section II pitch with respect to section I by about half a semitone. Next to these are the ring modulator and sub-oscillator (LFO) controls. Note that these slide controls are actually 'rotary cantilevers'; they do not move in a linear motion like the sustain and glissando/portamento controls on the lower panel. Instead, they move through an arc, as if they were rotary dial controls turned sideways--which is exactly what they are.
The ring modulator has its own attack-decay envelope with adjustable envelope depth, triggered by pressing keys. The envelope can adjust the speed of the ring modulator's carrier LFO, making for some very interesting sounds. The final control in the ring modulator section is the modulation amount to apply to the synthesizer sound.
The Sub-oscillator (LFO) has five waveforms (sine, saw, ramp, pulse, noise) plus a sixth selection for an external CV via a rear-panel jack. It has the traditional speed control and VCO, VCF and VCA modulation depth rotary sliders. The sub-oscillator is also linked to the keyboard touch response controls--see panel 3, below.
The above image is the first half of the main panel's complement of synthesizer voicing controls. On the upper part of the main panel can be seen two rows of identical controls: section I and section II. The sub-sections are indicated and are as follows:
The VCO for each section offers simultaneous, switchable variable-width (50% to 90%) pulse, sawtooth and sine outputs. (The sine waveform is actually controlled by a slider in the VCA section, see panel 3, below). The pulse waveform has pulse-width modulation speed and depth controls. A dedicated sine LFO (not a traingle LFO) is employed for each section's PWM circuit. The sine waveform allows for a greater range of usefulness of the PWM depth control: triangle PWM starts to sound too harsh past about 50% depth, whereas sine PWM depth does not sound 'overmodulated' until past 80% of depth.
Also, for each section there is a white noise level control.
The VCF for each section is comprised of 12dB/octave (2-pole) high-pass and low-pass state-variable filters, with controls for cutoff frequency and resonance. The resonance controls do not drive the filters into self-oscillation, due to external limiting resistors Yamaha placed on the gain cells of their IG00156 filter chips. This limitation was to allow the maximum amount of initial and aftertouch flexibility without accidentally overdriving the filter.
The VCF of each section has its own envelope generator (EG). The filter EG has controls for 'Initial Level' which allows the filter envelope to start at a point other than zero, and an 'Attack Level', which can place the attack phase at a point different than the selected initial level. The envelope itself is set by 'Attack', 'Decay' and 'Release' time-setting sliders. Filter sustain is under control of the performance controls described for Panel 3.
Below the section controls are the octave selectors (labeled Feet) and the 28 tone selector buttons. 11 tones for each section are presets. These preset tones, with careful attention to the settings of the performance controls can yield wonderful results. For example, Vangelis gets a lot of use out of the section I 'Flute' and section II 'Bass' presets. Each section also has two 'memory' settings, described in detail on Panel 4, below. Lastly, the two buttons labeled 'Panel' cause the voice program to be taken from the setting of the main panel controls for each section.
At the bottom of the Panel 2 image can be seen the black felt-covered pitch ribbon. The pitch ribbon control circuit remembers where the ribbon is initially touched and all tone portamento can go up or down from that point. Additionally, the pitch ribbon only affects keys currently held down. If, for example, you play a chord with the key release sustain set for a medium to long release rate (on Panel 1), let up the keys then play another note, the held note will respond to the pitchbend while the sustaining chord does not alter pitch. The range of the ribbon is about +1 octave but goes down in pitch all the way to zero.
Panel 3 shows the VCA controls, and the very important instrument-defining performance controls. The VCA has a mixer on the input of each section with level controls for the VCF signal and the VCO's pure sine signal. The sine signal, by the way, is not routed through the VCF due to the fact that a sine waveform is a pure tone with no harmonics in it at all. Thus, passing the sine through the filters would be pointless as there are no harmonics to remove or emphasize. The sine waveform is very useful nonetheless: it can restore the bass-end of a sound that has been attenuated by the VCF, for example. A patch can thus sound very vocal/sibilant (which uses a fair amount of bass-response-attenuating high-pass filter with resonance) without having to sacrifice the fullness of low-end 'support'. The VCA envelope generator (EG) is the classic ADSR type with Attack, Decay and Release time-setting controls and a Sustain level control. The VCA also has an output level control.
For each synthesizer section, there are a pair of 'initial' and 'after' response controls. Initial Brilliance routes a variable level of control voltage from the initial key velocity detection circuits to the high-pass/low-pass VCF pair to achieve a timbre response change, while the Initial Level routes a variable level of control voltage to the VCA to control a given key's volume level in proportion to the key strike velocity. The After(touch) Brilliance and After(touch) Level do the same thing based on key pressure after the note is played and held down. These controls are among the most important in defining "the sound" of a CS machine.
Perhaps most important of all are the eleven controls to the right of the tone selector buttons. These are the realtime performance controls. All performance controls work on panel, preset and 'memory' selections. One thing to note is that the performance controls, like those of the ring modulator and LFO, increase their values as the controls are pulled toward the keyboard. The controls are:
Mix I/II: Allows the two synthesizer sections to be layered together in any ratio. While playing, one can fade from one patch to another and back again seamlessly. When both sections are programmed to a similar voice, a few changes in the VCO PWM configuration or in the filter configuration in one section versus the other can yield some very profound depth/animation to the sound.
Brilliance and Resonance: Control the cutoff frequency and resonance of all filters globally. These two controls are arguably the most useful on the entire machine (well, OK, next the the power switch and volume control). With an imperceptible nudge, the same patch can take on shades of tone color simply unattainable otherwise. Want a trumpet to become sweeter as a song progresses? Nudge the resonance a bit each time a solo line is played. Want to take the 'glass' off a string section? ease up on the brilliance a bit and hear what the filters now do. Understand that these controls do not radically change the sound; rather, they change in it a subtle fashion. CS machines are subtle by nature. They are composer's instruments, where the 'delicacy of detail' lies in the ability to carefully explore the harmonic structure while retaining the overall desired sound.
Touch Response -- Initial Pitchbend: This control uses the key strike velocity control voltage to induce a brief portamento of a note from about 1 semitone below the key's actual pitch to the expect pitch. Such an effect allows for emulation of the brass and woodwind ombichure technique that induces a change in pitch at the beginning of a note. Call it a 'twang' if it helps to understand the effect better.