Combs
The comb filters are basically very short delays that operate at audio rate, i.e. only a couple of samples or milliseconds. If you just feed a short noise/impulse into such a delay and add some feedback you will get a tone much like an oscillator.
Zebra’s comb filters offer several modes. Up to 4 such short delays work together, in various circuits and always stereo. You can build envelope driven Flangers, plucked strings, flutes, percussions, bowed strings, metallic sounds, weird sounds, strange stuff and generally a whole range of sounds not possible in a typical synthesizer.
Tuning
The parameters in the first row are pretty much the same as the ones found in the oscillators. Tune ranges from -48 to +48 semitones, modulateable via the modulation knob next to it. Detune changes the microtuning of the stereo signal. Vibrato assigns LFO1 to modulate tuning by +/- 1 semitone. Keyscale determines how the comb filters pitch reacts to the note played. At 100 it is standard semitone per note.
Sound
Feedback controls the delay feedback. A Comb filter is a delay so this controls the amount of filtering.
The damp parameter is a lowpass filter of 6 db/octave that works on the feedback path.
The tone parameters function changes from mode to mode, see below for details. Normally this determines the ratio of several cascaded delays.
Distortion adds harmonics into the feedback. Use with caution.
Material
PreFill feeds white noise into the comb. This parameter is useful when synthesizing plucked strings.
Input controls the amount of signal from the channel i.e. noise, osc, etc. into the comb.
The flavour parameter like the tone parameter depends on the mode of the comb, see below for details. Typically this controls injection of the channels signal somewhere in between several comb stages/cascaded delays.
Mix
The dry knob sets the level of the passed through signal of the channel as it was before going into the comb.
The volume sets the volume of the combs output, the dry signal is not affected. Pan controls the panning of the signal. In split dual mode, width pans the two signals to the left and right channel.
Modes
- Comb
This is simple stereo delay, tuned to the played note. The tone and flavour parameters have no effect in this mode. - Split Comb
In this mode 2 delays feed into each other. The input is summed. The tone paramter controls the legnth ratios of the delays. The flavour parameter inserts xxx the input signal directly into the second delay. Outputs of each delay are left and right. - Split Dual
In this mode 2 stereo delays feed into each other like with the split comb. The difference is, that in this case there is true stereo operation. - Diff Comb
Works just like the split dual mode but in this mode the second delay is an allpass filter. This resulst in weird dissonant sounds. The flavour parameter controls the feedback of the allpass filter. The dissonant frequencies can dominate the fundamental frequency, thus you may have to tune this one accordingly. - Dissonant
This mode creates a 4 x 4 Feedback Delay Network. This will always sound metallic and dissonant. Tone and flavour determine the ratios of each delay line. It is inpossible to create any “nomal” sounds in this mode.