The S321 is a linear, exponential frequency modulation and phase modulation based voltage controlled oscillator. Phase modulation (PM) provides sounds reminiscent of the Yamaha(TM) DX7*. While linear and exponential FM can provide further complex sounds.
Six operators (Sin waves) are provided. Four of them can act as modulators. All modulation can be manually or CV controlled using a 6×4 matrix of knobs and CV input. Each CV has it’s own attenuator too.This is all done using phase modulation.
Additionally, operators 5 and 6 can be externally modulated using the op5 CV/knob and op6 CV/knob provided on the far bottom left of the panel. This is done with a certain type of linear FM method. The VCO can be further modulated using the FM CV/knob which is done using exponential FM method.
The matrix contains black and red knobs!!. The red knobs are meant for feedback modulation and therefore have a much lower depth than the black knobs (which are feedforward). This is to avoid the extremely violent sounds that usually produce just noise when feedback is dialed. Gray knobs are CV attenuators and follow there nearby black/red knob in function.
The digits LEDs infront of each operator specifies the Ratio. Which is a factor multiplied by the operators frequency.
Each operator (row) has a separate output. All outputs are summed using a mixer with a knob for each, which is sent to the mix out.
The sync button resets all operators to the same phase. While the random button randomizes the phases. This will give similar but not identical sounds every time.
The S321 internally uses some advanced methods to try to limit it’s CPU usage, both for knob automation and when some operators are not used. As a result when an operator is not used and then used again, it’s phase will be different than other operators. This can provide subtle changes in the sound which can be useful. However, if exact phases is required, you can still use the sync button after you reuse an operator. Note also that the linear FM used in op5 and op6 can still change the phase of those two operators.
*PM is usually wrongly labeled as FM. Under certain constraints they can provide the same exact sounds. Yet, they are totally different when those constraints are removed.