Octave provides a few functions for dealing with audio data. An audio `sample' is a single output value from an A/D converter, i.e., a small integer number (usually 8 or 16 bits), and audio data is just a series of such samples. It can be characterized by three parameters: the sampling rate (measured in samples per second or Hz, e.g. 8000 or 44100), the number of bits per sample (e.g. 8 or 16), and the number of channels (1 for mono, 2 for stereo, etc.).
There are many different formats for representing such data. Currently,
only the two most popular, linear encoding and mu-law
encoding, are supported by Octave. There is an excellent FAQ on audio
formats by Guido van Rossum <firstname.lastname@example.org> which can be found at any
FAQ ftp site, in particular in the directory
`/pub/usenet/news.answers/audio-fmts' of the archive site
Octave simply treats audio data as vectors of samples (non-mono data are not supported yet). It is assumed that audio files using linear encoding have one of the extensions `lin' or `raw', and that files holding data in mu-law encoding end in `au', `mu', or `snd'.
lin2mu (x)is the corresponding mu-law encoding.
mu2linconverts it to linear encoding. The optional argument bps specifies whether the input data uses 8 bit per sample (default) or 16 bit.
The extension ext determines how the data in the audio file is interpreted; the extensions `lin' (default) and `raw' correspond to linear, the extensions `au', `mu', or `snd' to mu-law encoding.
The argument bps can be either 8 (default) or 16, and specifies the number of bits per sample used in the audio file.
loadaudio); defaults are `lin' and 8, respectively.
The following functions for audio I/O require special A/D hardware and operating system support. It is assumed that audio data in linear encoding can be played and recorded by reading from and writing to `/dev/dsp', and that similarly `/dev/audio' is used for mu-law encoding. These file names are system-dependent. Improvements so that these functions will work without modification on a wide variety of hardware are welcome.
For example, if
vol corresponds to the volume property, you can
set it to 50 (percent) by
setaudio ("vol", 50).
This is an simple experimental program to control the audio hardware
settings. It assumes that there is a
mixer program which can be
mixer type value, and simply executes
system ("mixer type value"). Future releases might
get rid of this assumption by using the
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