This term is normally used to refer to the tradional synthesis model used by analog synthesizers in the 1970s. It is also known as subtractive synthesis. It involves oscillators, the outputs of which are mixed together and fed into a filter (where certain frequencies are subtracted) after which they are fed through an amplifier. The amplifier and filter are normally also driven by envelope generators....
SH-7
The SH-7 is a 2-VCO, duophonic analog synthesizer with a 3 1/2-octave, 44-note (F-C) keyboard. Both VCOs can
be switched between triangle, sawtooth, square, and pulse waveforms. VCO2 can be detuned from VCO1. Pulse-
width can be controlled by the LFO or ENV1 (envelope generator 1). Each VCO has three sliders that adjust how
much it is affected by the LFO, S/H, and a function called "Autobend". Autobend allows the VCO to slide up or
down to a pitch. The Autobend function has controls for polarity and time. VCO1 has an additional square wave
section (called VCO1B) wherein five sliders control the volume of each square wave (2', 4', 8', 16', and 32'). This
works in much the same way as an organ's drawbars do. The SH-7 also features a ring modulator where the first
input is VCO1 and the second is switchable between VCO2 and an external signal (via the external input jack in the
back). There is a switch for oscillator sync. However, it does not achieve the usual "sync" sound. A mixer section
provides five sliders, VCO1A, VCO1B, VCO2, Noise, and the last one switchable between the Ring Modulator and
the External Signal.
The SH-7 features a single VCF (self-oscillating, 24dB/octave) with five sliders controlling modulation, many of
them having a switch to choose between two options. The modulation sliders are for are the ENV1 (with switchable
polarity), LFO or S/H, Keyboard or optional pedal, VCO1 or noise, and an envelope follower from the external
signal (also with switchable polarity). The VCA can be controlled by either ENV1 or ENV2, and has a Hold button
and a slider for LFO amount. Both ENV1 and ENV2 are ADSR envelopes and each has three trigger options,
gate/trigger, gate, and LFO. The sample-and-hold section features three waveforms sources and an Output Lag slider
(a rare but extremely useful feature). The LFO can output sine, up-ramp, or pulse waveforms, and has controls for
rate and delay. Portamento can be set for just up, just down or both ways. The bender can be set to modulate the
VCO, VCF, and/or the VCA with varying amounts of control voltage or LFO signal.