MATRIXSYNTH: Modor eurorack-Noisy Oscillator & Comb Filter demo

Monday, July 15, 2019

Modor eurorack-Noisy Oscillator & Comb Filter demo


Published on Jul 15, 2019 Dziam Bass

"This video shows sound from the Noisy Oscillator and Comb filter from Modor modules eurorack.

A little added noise from the oscillator from the second voice as you see the knob mix and also subtle filtering from Comb Filter to get a partial flanger effect without too much modulation.

later we got a little more effect with Fb-feedback regulation and a larger delay type, ie a stronger effect on the longer time generated by Comb filter.

Noisy Oscillator module is and oscillator that mixes two signals: a 'regular' wave (sawtooth/square/triangle) and a 'tonal noisy' wave. This adds a special noisy layer over the sound, that adds 'air', grit or dirt, depending on the combinations you make. The MOD parameter acts on the noisy waveforms:

• Sonar Noise: a white noise filtered by a resonant bandpass filter, with 1V/oct tracking of the filter frequency. The MOD parameter controls the resonance.

• Wind Noise: white noise filtered by a comb filter, with 1V/oct tracking of the base frequency (delay). The MOD parameter controls a 6dB/oct hipass filter.

• Arcade Noise: LFSR noise source as can be found on the SID soundchips (Commodore) or Sega Arcade games. The MOD parameter controls again a 6dB/oct hipass filter.

The noisy wave can be set equal, or 1 or 2 octaves above the regular wave.

The module has two voices, with their own set of CV and output connectors. This can be used to play in a full 2-voice polyphony, or in a 2-voice unison. The outputs can be separate, using both output connectors, or mixed, using only the connector of the second voice.

Next to the 1V/oct pitch CV, the module offers CV control over pitch (FM), the MOD parameter and the sound level:

• FM CV: pitch control normalled to 0V, attenuated with the FM knob (+ and -). This allows for Frequency Modulation up to the lower audio range. It's of course a digital module, so higher frequencies can start inducing aliasing and digital artefacts.

• MOD CV: CV control for the MOD parameter, normalled to 0V and attenuated with the CV AMT knob (+ and -).

• LEVEL CV: CV control for the sound volume, normalled to 7.5V. With this CV control you can omit an external VCA stage if you want.

The CV signals of the second voice (upper row of connectors) are always normalled to the signal of the first voice (lower row), so you can use a single LFO for some FM vibrato or tremolo on both voices, for example. Only the V/oct connector of the second voice is normalled to the first voice with an extra addition of a fixed voltage that can be set using a trimmer at the backside of the module. This way you can use the 2 voices to play in unison with a fixed pitch separation you can set on the backside.

Comb filter is a digital filter where the input signal is mixed with a slightly delayed version of the input signal. You won't hear it as some kind of an echo, as this delay is very short (40ms at max). But the mixing process creates a number of equally spaced peaks and holes in the frequency spectrum, that make it look like the teeth of a comb. That's where the name 'Comb Filter' comes from.

Comb filters are typically used to make chorus and flanger style effects. These effects are created by modulating the delay time. With longer and relatively fast modulated delays you receive a chorus effect. With short to very short slowly modulated delays, combined with some feedback you'll get the typical sound of a flanger unit.
So, the most interesting parameter in this is the delay time. That determines the frequency spacing of the comb teeth. So that's why there's a CV control for it. The typical chorus and flanger effects are made by modulating the delay time with a triangle LFO. So there's a triangle LFO onboard the module, with speed control. If you don't enter any CV in the CV1 connector, it is normalled to this internal LFO to make typical effects. CV2 is normalled to the reverse signal of CV1, to make Modor's typical wide stereo effects, just as on the NF-1 synthesizer. But of course, you can enter your own CV signals in there: LFO's, Envelopes or some rhytmically undulating spacy voltage signals."

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