907a fixed filter bank

moog907a · filters

907A Fixed Filter Bank (moogafakkin System 35 clone — categorized under Ports -> moogafakkin). Non-VC fixed filter bank: a high-pass + low-pass + several fixed center-frequency band-pass cells (12 dB/oct), each with its own level knob, summed to one output. Shares the moog-filterbank center-frequency lib with the 914. Own-code (textbook biquad bank). Beige moogafakkin faceplate (the intrinsic always-on look shared by the moogafakkin module family).

A recreation of the Moog 907A Fixed Filter Bank — the System 35's smaller fixed filter bank, a kind of fixed graphic EQ for spectral and formant shaping. The signal fans into ten parallel filter sections whose centre frequencies DO NOT move: a fixed low-pass shelf at the bottom, eight fixed band-pass sections marching up the spectrum (250 Hz, 350, 500, 700, 1 kHz, 1.4 k, 2 k, 2.8 k), and a fixed high-pass shelf at the top. Each section has its own LEVEL knob, and all of them sum to one output, so you sculpt a sound by boosting and cutting fixed regions — emphasise a formant, notch out a harsh band, or carve a vocal/telephone tone. Unlike a voltage-controlled filter the bands never move and there is no CV: it is a pure Web Audio biquad + gain graph (the larger 914 is the same module with twelve bands). At the default 0.5 every section passes at half level — which is a neutral STARTING POINT, not a flat response, and the faceplate prints the difference. The sections are summed by fan-in, so they add as signals rather than as levels: at the shipped defaults the summed spectrum peaks at -4.1 dB near 1.4 kHz and has a -21.6 dB null at 209 Hz, in the gap between the 175 Hz low-pass corner and the 250 Hz first band. That gap is what the 914 fills with its extra 125 and 175 Hz bands, and it is the clearest audible difference between the two banks.

the faceplate

1 inputs · 1 outputs · 2 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 signal to filter — fanned in parallel into every fixed filter section. audio signal

outputs

id	cable	what it does
`audio`	audio	The summed multi-band output — every section's contribution added together, the shaped spectrum. audio signal

params

id	label	range	default	curve
`hp`	hp	0..1	0.5	linear
`lp`	lp	0..1	0.5	linear

controls

control	what it does
Band1	Level of the fixed 250 Hz band-pass section (low mids / body). Defaults to 0.5.
Band2	Level of the fixed 350 Hz band-pass section (lower mids). Defaults to 0.5.
Band3	Level of the fixed 500 Hz band-pass section (mids). Defaults to 0.5.
Band4	Level of the fixed 700 Hz band-pass section (mids). Defaults to 0.5.
Band5	Level of the fixed 1 kHz band-pass section (presence). Defaults to 0.5.
Band6	Level of the fixed 1.4 kHz band-pass section (presence / nasal). Defaults to 0.5.
Band7	Level of the fixed 2 kHz band-pass section (upper mids / bite). Defaults to 0.5.
Band8	Level of the fixed 2.8 kHz band-pass section (high presence). Defaults to 0.5.
hp	Level of the fixed HIGH-PASS section at the top of the bank (corner 6.6 kHz) — raise to add air and let the highs through, cut to tame them. It is a RESONANT high-pass rather than a flat shelf: measured +4.0 dB at its own corner, because the bank's shared Q is read in decibels by a high-pass. Defaults to 0.5.
lp	Level of the fixed LOW-PASS section at the bottom of the bank (corner 175 Hz) — raise to add weight and lows, cut to thin the bottom. Like the high-pass it is RESONANT rather than a flat shelf: measured +4.0 dB at its own corner, which is why the null just above it at 209 Hz is as deep as it is. Defaults to 0.5.

source

moog907a.ts on GitHub.