Feedback suppressor
Feedback suppressor: tracks howling tones and places up to eight narrow time-domain notches on them, with no added latency.
- Filter
- Since 0.2.0
- feedback
- howl
- ring out
- notch
- live sound
- microphone
- pa
Catch the howl of a microphone feeding back through speakers and notch it out before it takes over.
What it does#
The suppressor listens to its input in narrow frequency bins (4096-point analysis up to 48 kHz, 8192 above, about 12 Hz apart), a quarter frame at a time. It looks for the signs of feedback: a single peak between 60 Hz and 18 kHz, louder than −50 dBFS, that stands far above the average level, is much louder than the bins a few steps either side, and has no partner at twice or half its frequency. Notes have harmonics; feedback is a pure tone. A peak that keeps those signs for several frames places a 6 dB notch on its exact frequency, and each time it persists the notch deepens by 3 dB, up to Max depth.
The notches are narrow bell cuts that run on the audio itself, so the suppressor adds no latency. Depth changes glide at 3 dB per 10 ms. Once a howl stops, its notch recovers over Release and is freed. Every lane has its own detector and notches.
When to use it#
Use it in a live chain after a microphone: a talk-back mic, a vocal, a kit mic in a small room, or a Toy that routes its own output back into an input. It is not a substitute for good mic placement or a lower monitor level. To tame resonances in a mix rather than feedback, use the Resonance suppressor.
Ports#
| Port | Direction | Signal | Lanes |
|---|---|---|---|
audio | Input | Audio | Inferred from the cable |
audio | Output | Audio | Inferred from the cable |
Parameters#
| Parameter | Label | Range | Default | Unit | Scale | Notes |
|---|---|---|---|---|---|---|
sensitivity | Sensitivity | 0 to 1 | 0.5 | % | linear | How readily a steady, pure tone counts as feedback. Higher catches howls sooner but may notch held notes. Stored as a fraction; shown ×100 as a percentage. |
max_depth | Max depth | 3 to 40 | 18 | dB | linear | The deepest any notch may go. A notch deepens in steps while its howl persists. |
q | Q | 5 to 100 | 30 | Q | log | Notch width: 30 is about a twentieth of an octave. Higher is narrower and colours the sound less. |
notches | Notches | 1 to 8 | 6 | linear | How many notches may be active. When all are in use, a new howl replaces the shallowest notch. | |
release_s | Release | 1 to 120 | 20 | s | log | Time for a notch at Max depth to recover fully once its howl is gone. Notches that recover to nothing are freed. |
freeze | Freeze | 0 to 1 | 0 | linear | On holds every notch as it is: no new notches and no release. Choices: 0 Off, 1 On. | |
reset | Reset | 0 to 1 | 0 | linear | A change from Idle to Clear fades every notch out over 10 ms and starts tracking afresh. Choices: 0 Idle, 1 Clear. |
Sensitivity (sensitivity)#
How readily a steady, pure tone counts as feedback. Higher values react sooner and to quieter howls; lower values wait longer and may let a howl build. At 50 % a clear howl gets its first notch within about 0.2 seconds and 15 dB of cut within half a second.
Max depth (max_depth)#
The deepest any notch may go, from 3 to 40 dB.
Q (q)#
The width of every notch. 30 is about a twentieth of an octave. Higher values are narrower and take less of the music with them.
Notches (notches)#
How many notches may be active at once, from 1 to 8. When all are in use, a new howl takes over the shallowest notch.
Release (release_s)#
The time, in seconds, for a notch at Max depth to recover once its howl is gone. Long releases keep a room rung out; short ones give the sound back quickly.
Freeze (freeze)#
On holds every notch exactly as it is: no new notches and no release. Ring out the room, then freeze.
Reset (reset)#
A change from Idle to Clear fades every notch out over 10 ms and starts listening afresh. Bind it to a Trigger control.
Tips#
- Ring out before the show: raise the monitor level slowly until a howl starts, let the suppressor catch it, repeat, then switch Freeze on.
- Lower Sensitivity if held notes from a flute or synth get notched.
- The notches are kept only while the Toy runs. Run the ring-out again after reloading.
See also#
Parametric EQ, Resonance suppressor, Limiter, Compressor.
Help patches
Each help patch is an ordinary Toy that teaches one idea. The diagram shows the Patch; the preview shows its Frame. Open it in TuneToys to play and edit it.
1. Catch a howl
beginner Teaches: sensitivity, max_depth, freeze, reset
A pure 1250 Hz tone stands in for feedback over a saw and room noise; the suppressor notches it out.
MIDI1 lane
Audio2ch
Fundamental pitch, capped below Nyquist; detune uses cents. Range: 20–20000 Hz. Default: 220 Hz. Logarithmic scale. Units: Hz.
Hz
Output gain. Range: 0–0.5 ×. Default: 0.12 ×. Linear scale. Units: linear gain.
×
Continuous sine/triangle/saw/pulse morph; only its two neighboring waveforms are evaluated. Range: 0–3. Default: 0. Linear scale. Units: unitless. Marks: 0 Sine, 1 Triangle, 2 Saw, 3 Pulse.
Saw
Pulse duty cycle with a frequency-dependent safe edge width. Range: 0.05–0.95. Default: 0.5. Linear scale. Units: unitless.
Selects the implemented algorithm. Choices are discrete and are not LFO targets. Range: 0–7. Default: 0. Linear scale. Units: unitless.
Cycle offset; Gate rising edges restart phase from this position. Range: 0–1 cycles. Default: 0 cycles. Linear scale. Units: cycles.
cycles
Pitch offset in cents. Range: -1200–1200 cents. Default: 0 cents. Linear scale. Units: cents.
cents
On or off. A rising edge retriggers; held on runs the oscillator or envelope. A control cable switches it at 0.5. Range: 0–1. Default: 1. Linear scale. Units: unitless.
Semitones a full pitch bend on the MIDI input moves the note, up or down. Range: 0–48 st. Default: 2 st. Linear scale. Units: st.
st
Time constant of the slide from one MIDI note's pitch to the next; 0 jumps. Range: 0–2000 ms. Default: 0 ms. Linear scale. Units: ms.
ms
Audio2ch
Peak amplitude of white noise. Each channel and node path owns a repeatable independent stream; preparation restarts it. Range: 0–0.5 ×. Default: 0.12 ×. Linear scale. Units: linear gain.
×
MIDI1 lane
Audio2ch
Fundamental pitch, capped below Nyquist; detune uses cents. Range: 20–20000 Hz. Default: 220 Hz. Logarithmic scale. Units: Hz.
Hz
Output gain. Range: 0–0.5 ×. Default: 0.2 ×. Linear scale. Units: linear gain.
×
Continuous sine/triangle/saw/pulse morph; only its two neighboring waveforms are evaluated. Range: 0–3. Default: 0. Linear scale. Units: unitless. Marks: 0 Sine, 1 Triangle, 2 Saw, 3 Pulse.
Sine
Pulse duty cycle with a frequency-dependent safe edge width. Range: 0.05–0.95. Default: 0.5. Linear scale. Units: unitless.
Selects the implemented algorithm. Choices are discrete and are not LFO targets. Range: 0–7. Default: 0. Linear scale. Units: unitless.
Cycle offset; Gate rising edges restart phase from this position. Range: 0–1 cycles. Default: 0 cycles. Linear scale. Units: cycles.
cycles
Pitch offset in cents. Range: -1200–1200 cents. Default: 0 cents. Linear scale. Units: cents.
cents
On or off. A rising edge retriggers; held on runs the oscillator or envelope. A control cable switches it at 0.5. Range: 0–1. Default: 1. Linear scale. Units: unitless.
Semitones a full pitch bend on the MIDI input moves the note, up or down. Range: 0–48 st. Default: 2 st. Linear scale. Units: st.
st
Time constant of the slide from one MIDI note's pitch to the next; 0 jumps. Range: 0–2000 ms. Default: 0 ms. Linear scale. Units: ms.
ms
Audio2ch
Band.in2ch
dB
Position on a two-lane mix: −1 left, 0 centre, 1 right. Constant-power for a one-lane channel, balance for a two-lane one; ignored on other widths. Range: -1–1. Default: 0. Linear scale. Units: unitless. The ring fills from zero for this signed linear range. Manual editing is unavailable while this host owns the control.
Read only
Room.in2ch
dB
Position on a two-lane mix: −1 left, 0 centre, 1 right. Constant-power for a one-lane channel, balance for a two-lane one; ignored on other widths. Range: -1–1. Default: 0. Linear scale. Units: unitless. The ring fills from zero for this signed linear range. Manual editing is unavailable while this host owns the control.
Read only
Howl.in2ch
dB
Position on a two-lane mix: −1 left, 0 centre, 1 right. Constant-power for a one-lane channel, balance for a two-lane one; ignored on other widths. Range: -1–1. Default: 0. Linear scale. Units: unitless. The ring fills from zero for this signed linear range. Manual editing is unavailable while this host owns the control.
Read only
Mix output level in decibels, after every channel. −60 dB is off; 0 dB leaves the sum unchanged. Range: -60–12 dB. Default: 0 dB. Linear scale. Units: dB.
dB
Audio2ch
Audio2ch
How readily a steady, pure tone counts as feedback. Higher catches howls sooner but may notch held notes. Range: 0–100 %. Default: 50 %. Linear scale. Units: percent.
%
The deepest any notch may go. A notch deepens in steps while its howl persists. Range: 3–40 dB. Default: 18 dB. Linear scale. Units: dB.
dB
Notch width: 30 is about a twentieth of an octave. Higher is narrower and colours the sound less. Range: 5–100 Q. Default: 30 Q. Logarithmic scale. Units: Q.
Q
How many notches may be active. When all are in use, a new howl replaces the shallowest notch. Range: 1–8. Default: 6. Linear scale. Units: unitless.
Time for a notch at Max depth to recover fully once its howl is gone. Notches that recover to nothing are freed. Range: 1–120 s. Default: 20 s. Logarithmic scale. Units: s.
s
On holds every notch as it is: no new notches and no release. Range: 0–1. Default: 0. Linear scale. Units: unitless.
A change from Idle to Clear fades every notch out over 10 ms and starts tracking afresh. Range: 0–1. Default: 0. Linear scale. Units: unitless.
Audio2ch
Connections as text
- Oscillator “band” audio output connected to Mixer band.in input
- Noise audio output connected to Mixer room.in input
- Oscillator “howl” audio output connected to Mixer howl.in input
- Mixer audio output connected to Feedback suppressor audio input
- Feedback suppressor audio output connected to Patch outputs audio input
- The sine is a stand-in for feedback: steady, pure and loud. Within a fraction of a second a narrow notch lands on it and deepens to Max depth.
- The saw is left alone: its harmonics show it is a note, not a howl. Lower Sensitivity if held notes ever get notched.
- Freeze holds the notches once the room is rung out. Reset fades them all and starts listening afresh.
2. Shape the notches
intermediate Teaches: notches, q, release_s
Three howls, one coming and going: Notches limits how many are caught, Q sets their width and Release how long they stay.
Audio2ch
Peak amplitude of white noise. Each channel and node path owns a repeatable independent stream; preparation restarts it. Range: 0–0.5 ×. Default: 0.12 ×. Linear scale. Units: linear gain.
×
MIDI1 lane
Audio2ch
Fundamental pitch, capped below Nyquist; detune uses cents. Range: 20–20000 Hz. Default: 220 Hz. Logarithmic scale. Units: Hz.
Hz
Output gain. Range: 0–0.5 ×. Default: 0.12 ×. Linear scale. Units: linear gain.
×
Continuous sine/triangle/saw/pulse morph; only its two neighboring waveforms are evaluated. Range: 0–3. Default: 0. Linear scale. Units: unitless. Marks: 0 Sine, 1 Triangle, 2 Saw, 3 Pulse.
Sine
Pulse duty cycle with a frequency-dependent safe edge width. Range: 0.05–0.95. Default: 0.5. Linear scale. Units: unitless.
Selects the implemented algorithm. Choices are discrete and are not LFO targets. Range: 0–7. Default: 0. Linear scale. Units: unitless.
Cycle offset; Gate rising edges restart phase from this position. Range: 0–1 cycles. Default: 0 cycles. Linear scale. Units: cycles.
cycles
Pitch offset in cents. Range: -1200–1200 cents. Default: 0 cents. Linear scale. Units: cents.
cents
On or off. A rising edge retriggers; held on runs the oscillator or envelope. A control cable switches it at 0.5. Range: 0–1. Default: 1. Linear scale. Units: unitless.
Semitones a full pitch bend on the MIDI input moves the note, up or down. Range: 0–48 st. Default: 2 st. Linear scale. Units: st.
st
Time constant of the slide from one MIDI note's pitch to the next; 0 jumps. Range: 0–2000 ms. Default: 0 ms. Linear scale. Units: ms.
ms
MIDI1 lane
Audio2ch
Fundamental pitch, capped below Nyquist; detune uses cents. Range: 20–20000 Hz. Default: 220 Hz. Logarithmic scale. Units: Hz.
Hz
Output gain. Range: 0–0.5 ×. Default: 0.12 ×. Linear scale. Units: linear gain.
×
Continuous sine/triangle/saw/pulse morph; only its two neighboring waveforms are evaluated. Range: 0–3. Default: 0. Linear scale. Units: unitless. Marks: 0 Sine, 1 Triangle, 2 Saw, 3 Pulse.
Sine
Pulse duty cycle with a frequency-dependent safe edge width. Range: 0.05–0.95. Default: 0.5. Linear scale. Units: unitless.
Selects the implemented algorithm. Choices are discrete and are not LFO targets. Range: 0–7. Default: 0. Linear scale. Units: unitless.
Cycle offset; Gate rising edges restart phase from this position. Range: 0–1 cycles. Default: 0 cycles. Linear scale. Units: cycles.
cycles
Pitch offset in cents. Range: -1200–1200 cents. Default: 0 cents. Linear scale. Units: cents.
cents
On or off. A rising edge retriggers; held on runs the oscillator or envelope. A control cable switches it at 0.5. Range: 0–1. Default: 1. Linear scale. Units: unitless.
Semitones a full pitch bend on the MIDI input moves the note, up or down. Range: 0–48 st. Default: 2 st. Linear scale. Units: st.
st
Time constant of the slide from one MIDI note's pitch to the next; 0 jumps. Range: 0–2000 ms. Default: 0 ms. Linear scale. Units: ms.
ms
MIDI1 lane
Audio2ch
Fundamental pitch, capped below Nyquist; detune uses cents. Range: 20–20000 Hz. Default: 220 Hz. Logarithmic scale. Units: Hz.
Hz
Output gain. Range: 0–0.5 ×. Default: 0.12 ×. Linear scale. Units: linear gain.
×
Continuous sine/triangle/saw/pulse morph; only its two neighboring waveforms are evaluated. Range: 0–3. Default: 0. Linear scale. Units: unitless. Marks: 0 Sine, 1 Triangle, 2 Saw, 3 Pulse.
Sine
Pulse duty cycle with a frequency-dependent safe edge width. Range: 0.05–0.95. Default: 0.5. Linear scale. Units: unitless.
Selects the implemented algorithm. Choices are discrete and are not LFO targets. Range: 0–7. Default: 0. Linear scale. Units: unitless.
Cycle offset; Gate rising edges restart phase from this position. Range: 0–1 cycles. Default: 0 cycles. Linear scale. Units: cycles.
cycles
Pitch offset in cents. Range: -1200–1200 cents. Default: 0 cents. Linear scale. Units: cents.
cents
On or off. A rising edge retriggers; held on runs the oscillator or envelope. A control cable switches it at 0.5. Range: 0–1. Default: 1. Linear scale. Units: unitless.
Semitones a full pitch bend on the MIDI input moves the note, up or down. Range: 0–48 st. Default: 2 st. Linear scale. Units: st.
st
Time constant of the slide from one MIDI note's pitch to the next; 0 jumps. Range: 0–2000 ms. Default: 0 ms. Linear scale. Units: ms.
ms
Reset1 lane
Control1 lane
Cycle1 lane
Waveform of the oscillator. The random shapes draw a new value each cycle from a generator seeded by the node path, so every host and replay agrees. Range: 0–5. Default: 0. Linear scale. Units: unitless.
Cycles per second when Beats is 0. Range: 0.01–40 Hz. Default: 1 Hz. Logarithmic scale. Units: Hz.
Hz
Beats per cycle, synced to the shared transport. 0 uses Rate instead. Range: 0–64 beats. Default: 0 beats. Linear scale. Units: beats.
beats
Peak-to-peak amount of the output swing. Range: 0–1. Default: 1. Linear scale. Units: unitless.
Centre of the swing. Range: 0–1. Default: 0.5. Linear scale. Units: unitless.
Starting phase of the cycle, and where a Reset edge restarts it. Range: 0–1. Default: 0. Linear scale. Units: unitless.
Where the Triangle peaks, or how the Saw bends. 0.5 is the plain shape. Range: 0–1. Default: 0.5. Linear scale. Units: unitless.
Audio2ch
Audio2ch
Multiplies every audio channel. 0 silences the signal; 1 leaves its level unchanged. Range: 0–2 ×. Default: 1 ×. Linear scale. Units: linear gain.
×
Audio2ch
Room.in2ch
dB
Position on a two-lane mix: −1 left, 0 centre, 1 right. Constant-power for a one-lane channel, balance for a two-lane one; ignored on other widths. Range: -1–1. Default: 0. Linear scale. Units: unitless. The ring fills from zero for this signed linear range. Manual editing is unavailable while this host owns the control.
Read only
Low.in2ch
dB
Position on a two-lane mix: −1 left, 0 centre, 1 right. Constant-power for a one-lane channel, balance for a two-lane one; ignored on other widths. Range: -1–1. Default: 0. Linear scale. Units: unitless. The ring fills from zero for this signed linear range. Manual editing is unavailable while this host owns the control.
Read only
Gate.in2ch
dB
Position on a two-lane mix: −1 left, 0 centre, 1 right. Constant-power for a one-lane channel, balance for a two-lane one; ignored on other widths. Range: -1–1. Default: 0. Linear scale. Units: unitless. The ring fills from zero for this signed linear range. Manual editing is unavailable while this host owns the control.
Read only
High.in2ch
dB
Position on a two-lane mix: −1 left, 0 centre, 1 right. Constant-power for a one-lane channel, balance for a two-lane one; ignored on other widths. Range: -1–1. Default: 0. Linear scale. Units: unitless. The ring fills from zero for this signed linear range. Manual editing is unavailable while this host owns the control.
Read only
Mix output level in decibels, after every channel. −60 dB is off; 0 dB leaves the sum unchanged. Range: -60–12 dB. Default: 0 dB. Linear scale. Units: dB.
dB
Audio2ch
Audio2ch
How readily a steady, pure tone counts as feedback. Higher catches howls sooner but may notch held notes. Range: 0–100 %. Default: 50 %. Linear scale. Units: percent.
%
The deepest any notch may go. A notch deepens in steps while its howl persists. Range: 3–40 dB. Default: 18 dB. Linear scale. Units: dB.
dB
Notch width: 30 is about a twentieth of an octave. Higher is narrower and colours the sound less. Range: 5–100 Q. Default: 30 Q. Logarithmic scale. Units: Q.
Q
How many notches may be active. When all are in use, a new howl replaces the shallowest notch. Range: 1–8. Default: 2. Linear scale. Units: unitless.
Time for a notch at Max depth to recover fully once its howl is gone. Notches that recover to nothing are freed. Range: 1–120 s. Default: 4 s. Logarithmic scale. Units: s.
s
On holds every notch as it is: no new notches and no release. Range: 0–1. Default: 0. Linear scale. Units: unitless.
A change from Idle to Clear fades every notch out over 10 ms and starts tracking afresh. Range: 0–1. Default: 0. Linear scale. Units: unitless.
Audio2ch
Connections as text
- Noise audio output connected to Mixer room.in input
- Oscillator “low” audio output connected to Mixer low.in input
- Oscillator “mid” audio output connected to Gain audio input
- Control LFO control output connected to Gain @level input
- Gain audio output connected to Mixer gate.in input
- Oscillator “high” audio output connected to Mixer high.in input
- Mixer audio output connected to Feedback suppressor audio input
- Feedback suppressor audio output connected to Patch outputs audio input
- Three steady tones stand in for three feedback frequencies. The middle one sounds for 2.5 seconds, then rests for 2.5.
- With Notches at 2, only two can be caught; a new howl takes the shallowest notch. Raise it to 3 to catch all of them.
- Q narrows each notch so less of the music goes with it. Release is how long a notch takes to recover once its howl stops.
Related nodes
- Parametric EQ Parametric EQ with up to 32 reorderable RBJ bands: cuts, shelves, bells and notches, per-band bypass and output trim.
- Resonance suppressor Spectral resonance suppressor: finds narrow peaks that stand above the local spectral average and pulls them down dynamically, bin by bin.
- Limiter Linked or independent sample-peak limiting with hold and adaptive release.
- Compressor Peak/RMS compression with a sidechain key input, detector filtering, hold, adaptive release and channel linking.