Lowpass

Audio Single output Transform

Apply a low-pass filter with 3dB point frequency.

FFmpeg filter: lowpass — the official reference.

Add it to a graph. The explicit form works for every filter — bind it to its input and read the result from outputs():

$node   = $audio->addFilter(new Lowpass(…));
$result = $node->outputs()[0];

Shorthand. Single-output filters can skip the node — apply() returns the result stream directly:

$result = $audio->apply(new Lowpass(…));

When to use it

TODO — when this filter shines: what it’s the right tool for, what to reach for instead when it isn’t, and how it composes with neighbouring filters.

How to use it

TODO — prose: how the filter actually works and what its key parameters mean (the explanation FFmpeg’s terse option help omits).

Examples

TODO — runnable PHP, with the equivalent ffmpeg CLI alongside.

Gotchas

TODO

See also

TODO

Parameters

Parameter	Type	Default	Range / values	Description
frequency	float	500	0–999999	set frequency
width_type	LowpassWidthType	q	h, q, o, s, k	set filter-width type
width	float	0.707	0–99999	set width
poles	int	2	1–2	set number of poles
mix	float	1	0–1	set mix
channels	string	all	—	set channels to filter
normalize	bool	false	—	normalize coefficients
transform	LowpassTransformType	di	di, dii, tdi, tdii, latt, svf, zdf	set transform type
precision	LowpassPrecision	auto	auto, s16, s32, f32, f64	set filtering precision
blocksize	int	0	0–32768	set the block size

FFmpeg also names these options (use the parameter shown above): f → frequency, t → width_type, w → width, p → poles, m → mix, c → channels, n → normalize, a → transform, r → precision, b → blocksize.

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Maps to FFmpeg’s lowpass filter. Verified against ffmpeg n7.1.1.