3.2 Effect parameters

Most effects supported by the SoundFX plugin accept certain parameters. Those parameters are described in the synopsis section in the documentation of the individual sound effects. For example, the synopsis for the fade effect looks like this:

fade [type] fade-in-length [stop-position(=) [fade-out-length]]

In such an effect synopsis, brackets [ ] are used to denote parameters that are optional, braces { } to denote those that are both optional and repeatable, and angle brackets < > to denote those that are repeatable but not optional. Where applicable, default values for optional parameters are shown in parenthesis ( ).

The following parameters are used with, and have the same meaning for, several effects:

center[k]

See frequency.

frequency[k]

A frequency in Hz, or, if appended with "k", kHz.

gain

A power gain in dB. Zero gives no gain; less than zero gives an attenuation.

position

A position within the audio stream; the syntax is [=|+|-]timespec, where timespec is a time specification (see below). The optional first character indicates whether the timespec is to be interpreted relative to the start (=) or end (-) of audio, or to the previous position if the effect accepts multiple position arguments (+). The audio length must be known for end-relative locations to work; some effects do accept -0 for end-of-audio, though, even if the length is unknown. Which of =, +, - is the default depends on the effect and is shown in its syntax as, e.g., position(+).

Examples: =2:00 (two minutes into the audio stream), -100s (one hundred samples before the end of audio), +0:12+10s (twelve seconds and ten samples after the previous position), -0.5+1s (one sample less than half a second before the end of audio).

width[h|k|o|q]

Used to specify the band-width of a filter. A number of different methods to specify the width are available (though not all for every effect). One of the characters shown may be appended to select the desired method as follows: "h" for Hz, "k" for kHz, "o" for Octaves and "q" for Q-factor.

For each effect that uses this parameter, the default method (i.e. if no character is appended) is the one that it listed first in the first line of the effect's description.

Most effects that expect an audio position or duration in a parameter, i.e. a time specification, accept either of the following two forms:

[[hours:]minutes:]seconds[.frac][t]

A specification of "1:30.5" corresponds to one minute, thirty and a half seconds. The t suffix is entirely optional (however, see the silence effect for an exception). Note that the component values do not have to be normalized; e.g., "1:23:45", "83:45", "79:0285", "1:0:1425", "1::1425" and "5025" all are legal and equivalent to each other.

sampless

Specifies the number of samples directly, as in "8000s". For large sample counts, e notation is supported: "1.7e6s" is the same as "1700000s".

Time specifications can also be chained with + or - into a new time specification where the right part is added to or subtracted from the left, respectively: "3:00-200s" means two hundred samples less than three minutes.