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Effects

Flow provides built-in audio effects for processing buffers. Effects return a new buffer (non-destructive) and chain cleanly with the flow operator. Most effects live in @audio.

Reverb

Schroeder-style reverb with damping and mix controls:

use "@std"
use "@audio"

Buffer tone = (createSineTone 0.5 440.0 0.5)

Note: simple (room size only)
Buffer wet = (reverb tone 0.5)

Note: full control (roomSize, damping, mix)
Buffer wetFull = (reverb tone 0.7 0.3 0.5)
Parameter Range Description
roomSize 0.0 - 1.0 Simulated room size (0=small, 1=large)
damping 0.0 - 1.0 High-frequency absorption (default 0.5)
mix 0.0 - 1.0 Dry/wet mix (default 0.3)

Filters

Low-pass / High-pass / Band-pass

Buffer lp = (lowpass  tone 800.0)           Note: cutoff at 800 Hz
Buffer hp = (highpass tone 200.0)           Note: cutoff at 200 Hz
Buffer bp = (bandpass tone 200.0 2000.0)    Note: 200 Hz - 2000 Hz

Compressor

Reduces dynamic range by attenuating loud signals:

use "@std"
use "@audio"

Buffer tone = (createSineTone 0.5 440.0 0.5)
Double negTwelve = (sub 0.0 12.0)

Note: simple (threshold dB, ratio)
Buffer comp = (compress tone negTwelve 4.0)

Note: full (threshold, ratio, attack ms, release ms)
Buffer compFull = (compress tone negTwelve 4.0 5.0 50.0)
Parameter Unit Description
threshold dB Level above which compression engages (typically negative)
ratio N:1 Compression ratio (4.0 = 4:1)
attack ms How quickly the compressor reacts
release ms How quickly the compressor releases

Sidechain Compression

Compress one source using a separate control signal (e.g., duck a bass under a kick):

use "@std"
use "@audio"

Buffer kick = (createSineTone 0.1 60.0 0.9)
Buffer bass = (createSineTone 1.0 80.0 0.8)

Double negTwelve = (sub 0.0 12.0)

Note: basic sidechain (bass ducks under kick)
Buffer ducked = (sidechain bass kick negTwelve 4.0)

Note: with custom attack/release (ms)
Buffer ducked2 = (sidechain bass kick negTwelve 4.0 5.0 200.0)

Note: chainable
Buffer piped = bass -> (sidechain kick negTwelve 4.0)

Signatures

Signature Description
(sidechain Buffer source, Buffer trigger, Double threshold, Double ratio) -> Buffer Basic ducking
(sidechain ... + Double attackMs, Double releaseMs) -> Buffer Full control

The output buffer matches the source's frame count — it is not truncated to the trigger's length.

Delay

Feedback delay:

Buffer delayed = (delay tone 250.0 0.4 0.5)
Parameter Unit Description
time ms Delay time
feedback 0.0 - 1.0 Amount fed back (0 = single echo)
mix 0.0 - 1.0 Dry/wet mix

Gain

Apply gain in decibels:

Double negSix = (sub 0.0 6.0)
Buffer quieter = (gain tone negSix)     Note: -6 dB
Buffer louder  = (gain tone 6.0)        Note: +6 dB

Panning

Constant-power stereo panning. Range is -1.0 (hard left) to +1.0 (hard right):

use "@audio"

Buffer tone   = (createSineTone 0.5 440.0 0.8)
Buffer center = (pan tone 0.0)
Buffer left   = (pan tone -1.0)
Buffer right  = (pan tone 1.0)

Note: chainable
Buffer piped = tone -> (pan 0.3)

Mono inputs are promoted to stereo automatically.

pan is also a musical context block that applies to everything rendered inside it:

pan -0.5 {
    section leftPart {
        Sequence mel = | C4 E4 G4 |
    }
}

Fade In / Fade Out

Linear amplitude fades (duration in seconds):

Buffer faded    = tone -> fadeIn  0.5
Buffer fadedOut = tone -> fadeOut 0.5

Effect Chaining

Effects chain naturally left-to-right with ->:

use "@std"
use "@audio"

Buffer tone = (createSineTone 0.5 440.0 0.5)
Double negThree = (sub 0.0 3.0)

Buffer processed = tone
    -> lowpass 1000.0
    -> reverb 0.3
    -> (pan -0.2)
    -> gain negThree

Which reads: filter, then reverb, then pan, then gain.

A Longer Chain

use "@std"
use "@audio"

tempo 120 {
    timesig 4/4 {
        key Cmajor {
            section intro {
                Sequence mel = | C4 E4 G4 C5 |
            }
            Song song = [intro]
            Buffer raw = (renderSong song "piano")

            Buffer final = raw
                -> lowpass 2000.0
                -> reverb 0.3
                -> (pan 0.1)
                -> fadeIn 0.3
                -> fadeOut 0.5
        }
    }
}

Working with Negative Values

Flow has no negative literal syntax. Use (sub 0 N) or (sub 0.0 N):

Double negTwelve = (sub 0.0 12.0)   Note: -12.0 dB
Double negSix    = (sub 0.0 6.0)    Note: -6.0 dB

Effect Reference

Effect Signature Description
reverb (Buffer, Double) -> Buffer Reverb (room size)
reverb (Buffer, Double, Double, Double) -> Buffer Reverb (room, damping, mix)
lowpass (Buffer, Double) -> Buffer Low-pass (cutoff Hz)
highpass (Buffer, Double) -> Buffer High-pass (cutoff Hz)
bandpass (Buffer, Double, Double) -> Buffer Band-pass (low, high Hz)
compress (Buffer, Double, Double) -> Buffer Compressor (threshold, ratio)
compress (Buffer, Double, Double, Double, Double) -> Buffer Full compressor
sidechain (Buffer, Buffer, Double, Double) -> Buffer Sidechain compression
sidechain (Buffer, Buffer, Double, Double, Double, Double) -> Buffer Sidechain with attack/release
delay (Buffer, Double, Double, Double) -> Buffer Delay (time, feedback, mix)
gain (Buffer, Double) -> Buffer Gain in dB
pan (Buffer, Double) -> Buffer Stereo pan (-1 .. +1)
fadeIn (Buffer, Double) -> Buffer Linear fade-in (seconds)
fadeOut (Buffer, Double) -> Buffer Linear fade-out (seconds)

See Also

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