ferraus doppler

Doppler pitch and level trajectory of a moving source

Synopsis

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

Simulates a source moving past the listener: along a straight line that passes --pass-by metres away after starting --distance metres before the closest point, or around a circle of radius --distance whose centre is --pass-by metres from the listener. A variable fractional delay (speed of sound 343 m/s) produces the pitch change; --volume-by-distance scales level by 1/distance (loudest when closest). The output keeps the input length.

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

Examples

A source passing 2 m away at 20 m/s

ferraus doppler car.wav -o passby.wav

Circling the listener off-centre

ferraus doppler tone.wav --path circle --velocity 30m/s --distance 5m --pass-by 3m -o orbit.wav

A fast fly-by that starts 50 m away and passes 5 m from the listener

ferraus doppler engine.wav --velocity 40m/s --distance 50m --pass-by 5m -o flyby.wav

Only the Doppler pitch change, with the level kept constant

ferraus doppler siren.wav --volume-by-distance off -o pitch_only.wav

Options

Flag	Type	Default	Meaning
`--path`	line \| circle	`line`	Trajectory shape
`--velocity`	text	`20m/s`	Source speed in m/s
`--distance`	text	`10m`	Line: start distance before the closest point; circle: radius (metres)
`--pass-by`	text	`2m`	Line: closest distance to the listener; circle: centre offset (metres)
`--volume-by-distance`	on\|off	`on`	Scale the level with distance (on\|off)
`--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_doppler
Schema: ferraus schema doppler
Pipeline: { op: doppler, args: { ... } } (flag names with _ instead of -)
fx stage: yes

{"command": "doppler", "defaults": {"path": "line", "velocity": "20m/s", "distance": "10m", "pass_by": "2m", "volume_by_distance": "on", "mix": "100%"}}