ferraus fft-filter

Filter by a drawn magnitude curve

Synopsis

ferraus fft-filter <input> [options] [-o <output>]

Draws a magnitude response from 'frequency:gain' points (joined linearly over log-frequency and held flat beyond the ends), designs a linear-phase FIR of half the FFT size, and applies it by FFT overlap-add without shifting the signal.

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

Examples

Steep band-limit between 80 Hz and 12 kHz

ferraus fft-filter in.wav --curve "20Hz:-30dB,80Hz:0dB,12kHz:0dB,16kHz:-30dB" -o band.wav

Narrow cut around 400 Hz with a long filter

ferraus fft-filter in.wav --curve "200Hz:0dB,400Hz:-8dB,800Hz:0dB" --fft 16384 -o out.wav

A gentle radio-voice band shape

ferraus fft-filter voice.wav --curve "100Hz:-12dB,300Hz:0dB,3kHz:0dB,5kHz:-12dB" -o radio.wav

A shallow bass dip, with a long FFT for resolution in the low end

ferraus fft-filter mix.wav --curve "40Hz:0dB,60Hz:-4dB,90Hz:0dB" --fft 32768 -o mix_dip.wav

Options

Flag	Type	Default	Meaning
`--curve`	text	`20Hz:0dB,120Hz:-6dB,1kHz:0dB,8kHz:+3dB`	Points as frequency:gain, e.g. "20Hz:0dB,120Hz:-6dB,1kHz:0dB,8kHz:+3dB"
`--fft`	integer	`4096`	FFT size (power of two); the filter is half as long Range: 256..65536.
`--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.

For models

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

{"command": "fft-filter", "defaults": {"curve": "20Hz:0dB,120Hz:-6dB,1kHz:0dB,8kHz:+3dB", "fft": "4096", "mix": "100%"}}