Sidechain Ducking in FL Studio: Routing, Three Control Methods and a Measured Example

Kick and bass can contain strong low frequencies at the same time. Their signals may reinforce or partly cancel each other, depending on timing and phase. Sidechain ducking briefly lowers the bass when the kick plays. A sidechain is an additional control signal: the kick determines the gain reduction while the compressor processes the bass. This can reduce overlap or create deliberate audible pumping.

This article describes three FL Studio options: Fruity Limiter, Fruity Compressor and Fruity Peak Controller. The first two use an additional audio signal to control compression. Peak Controller instead drives a linked parameter. Operating details follow Image-Line’s online manual; the measurement example is a separate simulation, not a test of these plugins.

What ducking changes in the measured example

The example contains sixteen 4/4 bars at 128 BPM: 30 seconds at 48 kHz. Both channels are identical. A sine-based kick falls from 150 to 50 Hz; the continuous bass contains 55, 110 and 165 Hz. On every beat, bass gain jumps to the selected reduction and returns linearly in dB. This return duration is called “release” here, but does not reproduce a plugin time constant. The linked meter’s archived calculation core supplies readings using the BS.1770 method. True peak also estimates peaks between stored samples; 0 dBTP is the full-scale reference. LUFS describes measured loudness, and LU its change. PLR is true peak minus integrated loudness, calculated from unrounded values. Related: LUFS and True Peak Meter

Without ducking, true peak is +2.16 dBTP; with 8 dB reduction and a 150 ms return it is −0.45 dBTP, a decrease of about 2.6 dB. Loudness falls by 0.59 LU. At 350 ms, the peak remains the same to one decimal place, while loudness falls by 1.52 LU overall. Audibility was not tested. The direction is not universal: other signals and phase relationships may behave differently. The model stores floating-point values above 0 dBFS and contains abrupt changes at beat boundaries; a fixed-point export of the unducked version would clip without prior level adjustment.

Assigning kick and bass separately

The mixer setup described here places kick and bass on separate insert tracks. This keeps the kick available as a control signal while the effect processes only the bass. A routing field showing “—” in the Channel Rack indicates a direct master assignment.

1. The channel selector in the Channel Rack marks the kick channel.
2. A right-click on the intended mixer track opens its context menu. Channel routing › Route selected channels to this track assigns the selected channel there. The listed shortcut is Ctrl+L; its action depends on the active window.
3. The bass receives another mixer track in the same way. Names such as “Kick” and “Bass” make later sidechain selection easier. F2 opens renaming for the selected track.

Creating the sidechain connection

The connection supplies the kick signal to a sidechain input on the bass track. Its ordinary audible send level is 0%. This does not mute the control signal: audible send and sidechain are separate paths. A plugin could explicitly monitor the sidechain audio; normal compression control does not mix the kick into the bass output.

1. The kick track is selected in the mixer first.
2. A right-click on the send switch at the bottom of the bass track opens the routing menu.
3. Sidechain to this track creates the connection from the selected kick track to the bass track.

This choice preserves the kick’s existing master route. Sidechain to this track only additionally disables the direct master route and suits an inaudible control track. Other audible routes through other tracks may still exist. An ordinary send also becomes a sidechain-only path when its audible send level is 0%.

Option 1: Fruity Limiter’s COMP tab

Fruity Limiter contains a compressor, limiter and gate. The sidechain controls compression; the other stages can still affect the bass.

1. Fruity Limiter occupies a free effect slot on the bass track. Each mixer track provides ten slots.
2. The COMP tab shows compression controls.
3. A right-click on SIDECHAIN lists available source tracks. After “Kick” is selected, its signal controls compression of the bass.
4. A THRESH setting below the detected kick level and a RATIO above 1:1 allow gain reduction. The depth reached also depends on timing and knee shape. The manual states that maximum THRESH disables compression.

The envelope describes gain changing over time. ATT controls the onset of compression and REL its recovery. Very short timings can cause distortion. CURVE changes the shape of these transitions; SUSTAIN affects averaging in level detection. RMS describes signal strength calculated across samples, rather than a single peak value. A release setting does not guarantee that the bass fully recovers after exactly that duration.

Show analysis & gain envelopes displays the analysis and gain curves; the white curve shows reduction. Lookahead delays the audio path so that an upcoming peak can trigger control in time. In Fruity Limiter, LIMIT-ATT sets this lookahead, not COMP-ATT. The manual describes maximum CEIL and minimum LIMIT-ATT as effectively bypassing the limiter stage; the gate and other controls still require separate consideration.

Option 2: Fruity Compressor with sidechain input

Fruity Compressor also provides a Sidechain Input. The feature already appears in the change log for beta 25.1.99 of 15 October 2025 and is included in the later 25.2 branch. Mixer routing stays the same, with “Kick” selected in the plugin’s sidechain menu. The following ranges come from the manual:

Type determines the transition into compression. The /R variants enable TCR, which automatically adjusts recovery time. This can reduce rapid gain changes and audible pumping, but does not prevent ducking altogether. Comparing /R and non-/R settings reveals which curve suits the intended sound. Vintage describes a particular transfer curve, not a complete replica of an analogue device.

Option 3: Fruity Peak Controller

Peak Controller converts input level into a control value for linkable parameters. Bass volume is one example; filter cutoff is another. No additional sidechain audio route is required. The connection uses an internal controller.

1. Peak Controller sits on the kick track and receives the control signal there.
2. According to the manual, MUTE is enabled by default and interrupts audio passing through the plugin. Control values are still generated. An audible kick requires MUTE to remain off.
3. A right-click on the target parameter opens Link to controller. Peak Ctrl – Peak provides level-dependent control. Peak Ctrl – LFO instead supplies a freely oscillating signal that does not necessarily follow the kick hits.
4. Negative VOL makes the control value fall as input peaks rise. BASE sets the resting value, DECAY the recovery and TENSION its shape. Mapping to the target determines actual reduction in dB. The bass’s resting level therefore needs checking after linking: a normalised control value of 100% does not automatically mean 0 dB gain on a mixer fader.

The manual specifies −50 dB as the lower input threshold for level detection. The relevant signal is the input at Peak Controller, including any earlier effects. The kick-track fader follows these effects and therefore does not change this input level. The controller’s Ramp function can also smooth rapid control changes if audible jumps occur.

Ghost kick: control without an audible kick

A ghost kick is a separate control track whose rhythm can differ from the audible kick. A short sample on its own mixer track drives the bass through Sidechain to this track only, removing the direct master route. A genuinely inaudible ghost kick must have no other audible outputs, such as bus routes; the source itself must continue playing.

Tempo as a guide to return time

BPM counts beats per minute. For quarter-note beats, 60,000 divided by BPM gives the spacing in milliseconds. The table lists note lengths, not ready-made compressor settings. In a real compressor, recovery begins and develops according to the control signal, threshold and processing model. A short numerical setting alone does not guarantee full recovery before the next beat.

The linked BPM calculator adds other tempos and dotted or triplet note lengths. These times provide a reference; the actual behaviour needs assessment from the gain curve and the sound. Related: BPM to Delay Time Calculator

Possible causes of unexpected behaviour

Assessing the finished export

Ducking can change peaks, loudness and sound. Assessment should therefore cover the complete mix and exported audio. A LUFS and true-peak meter supplies level readings; loudness matching supports listening comparisons. A displayed streaming-normalisation result remains a model for particular settings, not a guarantee for every playback situation. Related: LUFS and True Peak Meter

Fruity Limiter and Fruity Compressor use the same kind of mixer connection, but switching plugins still requires input selection and suitable settings. Peak Controller drives a target parameter, making its mapping and resting value important too. The appropriate method depends on the intended reduction and workflow.