SVF

The SVF SynthEdit module was developed to be a fast 2 pole filter, quite similar to the native SV Filter. Its main advantages are fast performance even with audio rate modulation, and good bass response (unlike the unstability of biquad filters at low frequencies and high resonance settings.)

The lowpass and highpass slopes are 12dB/octave, and the bandpass slopes are 6dB/octave.

Differences to the native SV Filter: - Better performance on P4, especially when more outputs are used at the same time - Resonance can be set in decibels (default), or as Q factor - Can work at different rates for CPU saving - The upper frequency limit is lower, about samplerate/4 (11k at 44k). This results in less high-frequency ringing, especially for bandpass and highpass outputs

Pitch: Can be set in kHz, or in 1 Volt/Octave mode, where 5 volts = 440 Hz. Upper frequency limit is about samplerate/4 (so at 44k rate, it is about 11 kHz). Due to an optimization, there's a little tuning error for very high frequencies (similarly as in SV Filter).

Resonance: In 1 Volt/4 dB mode, resonance is set in decibels. 0 volt means flat passband (Butterworth character), 1 volt is 4dB resonance, 2 volts is 8 dB resonance and so on. So 10 volts is 40dB. Upper limit is 15 volts (60 decibels).

Note that negative values are also valid, resulting in a softer 'knee'. So the usable range is about -2 .. 10 volts.

Freq Scale: 1 Volt/kHz selects linear freqency scale, 1 Volt/Octave selects exponential frequency scale.

Resolution: Sets the update rate of the filter. Samplerate is best for very fast modulation, but also means more CPU use. If there's no fast modulation, you can set it to lower to save CPU.

Lowpass, Highpass, Bandpass, Bandreject: The filtered signal.

Usage notes Please note that state variable filters are so called all-pole filters, meaning their frequency response is not completely linear. High frequencies get boosted by some decibels, mainly for the bandpass and highpass outputs. This can be as much as +10 decibels near nyquist. I strongly suggest NOT cascading more bandpass or highpass stages, as this can result in serious high frequency ringing.

The most usable output is the lowpass, which is more-or less balanced through all the frequency range. If you need precise high-frequency performance, especially in bandpass and highpass modes, then another filter (possibly a biquad) may be a better choice.

Also note: the Bandreject mode works correctly only for Q values greater than 1, below that, there is a tuning error. This is due to the stability limit of the state variable filters.