Noise

1. Density Knob Controls the probability that a random sample will be generated. White noise when fully clockwise.
2. Low-Pass Filter Cutoff Knob 12 dB/oct low-pass filter for the noise.
3. Low-Pass Filter Q Knob Quality factor (resonance) of the low-pass filter.
4. High-Pass Filter Cutoff Knob 12 dB/oct high-pass filter for the noise.
5. High-Pass Filter Q Knob Quality factor (resonance) of the high-pass filter.
6. Level Knob ±20dB output level trim to compensate for the effect of the filters
7. CV Output Random noise between -5V and 5V, running at CV rate. Optimized as a CV modulation source.
8. Audio Output Random noise between -5V and 5V, running at audio rate. Optimized as an audio noise source.

Overview ⚓︎

This is an adaptation of the unique noise source from AAS Chromaphone paired with a low-pass and a high-pass filter.

In its initial configuration (Density and Low-Pass Filter fully clockwise, High-Pass Filter fully counterclockwise), the filter outputs white noise between -5V and 5V. The density factor can bring the random event density down to an average of about one event per second, and the filters can be used to further shape the noise.

In Depth ⚓︎

Density ⚓︎

The Density knob controls the random event density. This is where the magic happens.

Unlike most digital random noise generators that generate a new random number for each output sample, our random number generator is triggered randomly, and the probability of being triggered at a particular moment is set with the Density knob.

When fully clockwise, the Audio output will behave like a white noise generator over the hearing range, and the CV output will produce white noise running at CV rate. As the knob is turned counterclockwise, fewer random events will be triggered. When the knob is turned fully counterclockwise, the module produces an average of about one random voltage per second. Between each random click, the output falls back to 0V.

If you wish to have fewer than 1 random event per second, you can connect the + output of a Voltage Source to a modulation input of the Density module, adjust the modulation input’s attenuverter to -100% and set Density to 0%. Turning the voltage source knob clockwise will further reduce the density.

Filtering ⚓︎

The noise generator is connected in series to a low-pass and a high-pass filter, both with a 12dB/oct slope. These filters can be used to shape the noise or to create special effects.

The low-pass filter will remove high frequencies from the noise, and the high-pass filter will remove low frequencies. The cutoff frequency for the CV output is 20 times lower than for the Audio output. For example, if you set the low-pass filter frequency to 1000 Hz, then the CV output will actually be filtered at 50 Hz.

The low-pass filter can be bypassed by setting its knob fully clockwise, and the high-pass filter can be bypassed by setting its knob fully counterclockwise.

The Q knobs control the quality factor—or resonance—of the filters. At their default value (when double-clicking on the knob), there is no resonance and there is a -3 dB attenuation at the cutoff frequency.

Try setting the low-pass and high-pass filters with a medium cutoff frequencies and a high Q, and connect the Audio output of the filter to the Output module. If the noise density is low, it will sound somewhat like chimes. If the noise density is high, it will sound like a whistle.

Outputs ⚓︎

When the filter knobs are in their initial position, the output is from -5V to 5V, and has a uniform distribution.

As you start applying filtering to the noise, the output amplitude may change. Use the Level knob to adjust it to the desired range. You can monitor the output amplitude by using a Level module.

The module contains two fully independent noise generators for the Audio and CV outputs.

When connecting a low-density noise source to the modulation input of a knob, use the CV output on the noise module. The modulation inputs on knobs don’t react quickly enough to handle low-density audio-rate noise.