ferraus dynamics

Transfer-curve dynamics: compressor, expander, and gate from one curve

Synopsis

ferraus dynamics <input> [options] [-o <output>]

Maps the detected input level to an output level through a curve of 'input:output' dB points (a slope below 1 compresses, above 1 expands, a drop to -100 gates). Outside the points the curve continues at unity slope. --spline smooths the curve through the points. The detector can be limited to a frequency band with --band; the gain is applied to the full signal, with lookahead so attacks are caught. The rms detector reads a full-scale sine at -3 dBFS.

This command is also an fx stage and a pipeline op: ferraus fx in.wav -o out.wav --fx "dynamics:key=value".

Examples

2:1 compression above -20 dB

ferraus dynamics vox.wav --curve "-100:-100,-20:-20,0:-10" -o comp.wav

A gate at -50 dB from the same command

ferraus dynamics drums.wav --curve "-100:-100,-50:-100,-45:-45,0:0" --spline off --detector peak -o gated.wav

2:1 compression above -30 dB that only reacts to the low end (40-250 Hz)

ferraus dynamics bass.wav --curve "-100:-100,-30:-30,0:-15" --band 40Hz..250Hz --detector peak -o bass_comp.wav

Gentle downward expansion below -40 dB, with no compression above

ferraus dynamics vox.wav --curve "-100:-100,-60:-70,-40:-40,0:0" --attack 2ms --release 150ms -o vox_exp.wav

Options

Flag	Type	Default	Meaning
`--curve`	text	`-100:-100,-40:-50,0:-10`	Transfer curve as input:output dB points, e.g. -100:-100,-20:-20,0:-10
`--spline`	on\|off	`on`	Smooth the curve through the points (on) or join them with straight lines (off)
`--attack`	time	`10ms`	Detector attack time
`--release`	time	`100ms`	Detector release time
`--lookahead`	time	`5ms`	How far ahead the gain reacts (time); no added latency
`--detector`	rms \| peak	`rms`	Level detector
`--band`	text	`20Hz..20kHz`	Frequency band the detector listens to (low..high)
`--mix`	percent	`100%`	Dry/wet balance: 0% returns the input unchanged, 100% is fully processed

Global options

Every command also accepts the global options (-o, --json, --dry-run, --overwrite, --progress, ...). See Global options.

Exit codes

Code	Meaning
0	Success
1	Processing failed
2	Usage or parameter error
3	Input missing or unreadable
4	Unsupported format or codec
8	Cancelled
70	Internal error (bug)

Common mistakes

Forgetting that outputs are never overwritten: pass --overwrite or a new -o path when re-running.
Beat-based times (4b, 1/4) need a tempo: pass --bpm or write 4b@120.

For models

MCP tool: ferraus_dynamics
Schema: ferraus schema dynamics
Pipeline: { op: dynamics, args: { ... } } (flag names with _ instead of -)
fx stage: yes

{"command": "dynamics", "defaults": {"curve": "-100:-100,-40:-50,0:-10", "spline": "on", "attack": "10ms", "release": "100ms", "lookahead": "5ms", "detector": "rms", "band": "20Hz..20kHz", "mix": "100%"}}