923 filters / noise source

moog923 · filter

923 Filters / Noise Source (moogafakkin System 35 clone — categorized under Ports -> moogafakkin). White + pink noise outputs PLUS a fixed filter utility on an external audio input: independent low-pass and high-pass taps with LO PASS / HI PASS cutoff knobs (log-mapped ~40 Hz-20 kHz). Own-code (noise generator + biquad filters). Beige moogafakkin faceplate (the intrinsic always-on look shared by the moogafakkin module family).

A recreation of the Moog 923 Filters / Noise Source — a dual-purpose utility panel from the System 35. It does two unrelated jobs at once. First, a NOISE SOURCE: white and pink noise generators on two independent outputs, both scaled by one LEVEL knob — the raw material for percussion, wind, snare bodies, and sample-and-hold. Second, a simple FIXED FILTER section: one external audio input fanned into a low-pass and a high-pass filter, each with its own frequency knob and its own output, so you can split a signal into low and high bands or just tame one end. The noise and the filter share no signal path — they are bundled on one panel for convenience, and the LEVEL knob is the noise half's alone. TWO THINGS WORTH KNOWING BEFORE YOU PATCH IT. First, the two noise taps are NOT level-matched: one knob drives both, but pink lands 12.3 dB below white at every setting, so equal channel gains do not give equal loudness. Second, the frequency a filter knob sets is where that filter is +1.0 dB, not where it is -3 dB: both filters run at the Web Audio default resonance, which puts a 2.0 dB hump about a third of an octave inside each passband and moves the real -3 dB point to 1.33x the knob's frequency on the low-pass and 0.75x on the high-pass. The faceplate prints the real ones. It is pure Web Audio (looping noise buffers + two biquads), no worklet.

the faceplate

1 inputs · 4 outputs · 3 params

about this module

Hover a control, or open the patch panel and hover a jack.

inputs

id	cable	what it does
`audio`	audio	The external signal fed through the filter section — it fans into BOTH the low-pass and the high-pass at once (the signal being filtered, not a modulator). audio signal

outputs

id	cable	what it does
`white`	audio	Full-spectrum white noise, scaled by the LEVEL knob — equal energy per Hz, bright and hissy. The LOUDER of the two noise taps by 12.3 dB, and the one a lane meter would read, since it is the first audio output declared. audio signal
`pink`	audio	Pink (1/f) noise, scaled by LEVEL — −3 dB/octave, warmer and more natural-sounding than white, good for wind and rumble. The QUIETER tap: 12.3 dB below white from the same LEVEL setting. audio signal
`lp`	audio	The audio input passed through the LOW-PASS filter, its frequency set by the LO PASS knob — the low band of the input. Silent until something is patched into the audio input, and unaffected by LEVEL. Its real −3 dB point sits 1.33x above the knob's frequency, with a 2.0 dB lift a third of an octave below it. audio signal
`hp`	audio	The audio input passed through the HIGH-PASS filter, its frequency set by the HI PASS knob — the high band of the input. Silent until something is patched into the audio input, and unaffected by LEVEL. Its real −3 dB point sits at 0.75x the knob's frequency, with a 2.0 dB lift a third of an octave above it. audio signal

params

id	label	range	default	curve
`level`	Level	0..1	0.8	linear
`lpCutoff`	Lo Pass	0..1	0.5	linear
`hpCutoff`	Hi Pass	0..1	0.5	linear

controls

control	what it does
Hi Pass	Where the HIGH-PASS gives up, for the filter section's hp output. The 0..1 knob maps log across ~40 Hz to 20 kHz; raise it to thin the hp output, lower it to let more low end through. Same shape mirrored: +1.0 dB at the knob's frequency, −3 dB at 0.75x it, and a 2.0 dB lift a third of an octave above. Defaults to 0.5, which is 894 Hz on the knob and 672 Hz at −3 dB — so at the shipped settings the two taps OVERLAP by 0.8 of an octave rather than meeting cleanly.
Level	Master gain on BOTH noise taps (white and pink) — sets the loudness of the noise outputs together. Equally in the sense of one multiplier, NOT one loudness: the two tables have different RMS, so the taps stay 12.3 dB apart at every setting. Does NOT affect the filter section at all — patch a signal in and the lp and hp outputs are identical at LEVEL 0 and at LEVEL 1. Defaults to 0.8.
Lo Pass	Where the LOW-PASS gives up, for the filter section's lp output. The 0..1 knob maps log across ~40 Hz to 20 kHz; lower it to darken the lp output, raise it to let more through. It is NOT the −3 dB point: the filter reads +1.0 dB at the knob's own frequency and does not fall 3 dB until 1.33x above it, having lifted 2.0 dB a third of an octave below. Defaults to 0.5, which is 894 Hz on the knob and 1.2 kHz at −3 dB.

source

moog923.ts on GitHub.