Node:Audio Processing, Next:Quaternions, Previous:Image Processing, Up:Top
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 <guido@cwi.nl> which can be found at any
FAQ ftp site, in particular in the directory
/pub/usenet/news.answers/audio-fmts
of the archive site
rtfm.mit.edu
.
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, n) | Function File |
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. |
mu2lin (x, bps) | Function File |
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. |
loadaudio (name, ext, bps) | Function File |
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 The argument bps can be either 8 (default) or 16, and specifies the number of bits per sample used in the audio file. |
saveaudio (name, x, ext, bps) | Function File |
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
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.
playaudio (name, ext) | Function File |
playaudio (x) | Function File |
Plays the audio file name.ext or the audio data
stored in the vector x.
|
record (sec, sampling_rate) | Function File |
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. |
setaudio ([w_type [, value]]) | Function File |
Execute the shell command mixer [w_type [, value]]
|