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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'.
Converts audio data from linear to mu-law. Mu-law values use 8-bit
unsigned integers. Linear values use n-bit signed integers or
floating point values in the range -1<=x<=1 if n is 0.
If n is not specified it defaults to 0, 8 or 16 depending on
the range values in x.
See also: mu2lin, loadaudio, saveaudio, playaudio, setaudio, record.
Converts audio data from linear to mu-law. Mu-law values are 8-bit
unsigned integers. Linear values use n-bit signed integers
or floating point values in the range -1<=y<=1 if n is 0. If
n is not specified it defaults to 8.
See also: lin2mu, loadaudio, saveaudio, playaudio, setaudio, record.
Loads audio data from the file `name.ext' into the vector x.
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.
See also: lin2mu, mu2lin, saveaudio, playaudio, setaudio, record.
Saves a vector x of audio data to the file
`name.ext'. The optional parameters ext and
bps determine the encoding and the number of bits per sample used
in the audio file (see
loadaudio); defaults are `lin' and
See also: lin2mu, mu2lin, loadaudio, playaudio, setaudio, record.
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.
Plays the audio file `name.ext' or the audio data
stored in the vector x.
See also: lin2mu, mu2lin, loadaudio, saveaudio, setaudio, record.
Records sec seconds of audio input into the vector x. The
default value for sampling_rate is 8000 samples per second, or
8kHz. The program waits until the user types RET and then
immediately starts to record.
See also: lin2mu, mu2lin, loadaudio, saveaudio, playaudio, setaudio.
Execute the shell command `mixer [w_type [, value]]'
Load the RIFF/WAVE sound file filename, and return the samples in vector y. If the file contains multichannel data, then y is a matrix with the channels represented as columns.
Additionally return the sample rate (fs) in Hz and the number of bits per sample (bits).
Read only the first n samples from each channel.
Read only samples n1 through n2 from each channel.
Return the number of samples (n) and channels (ch)
instead of the audio data.
See also: wavwrite.
Write y to the canonical RIFF/WAVE sound file filename
with sample rate fs and bits per sample bits. The
default sample rate is 8000 Hz with 16-bits per sample. Each column
of the data represents a separate channel.
See also: wavread.
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