@c DO NOT EDIT!  Generated automatically by munge-texi.

@c Copyright (C) 1996, 1997, 1999, 2000, 2002, 2005, 2007 Kurt Hornik
@c
@c This file is part of Octave.
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@c You should have received a copy of the GNU General Public License
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@c <http://www.gnu.org/licenses/>.

@c Written by Kurt Hornik <Kurt.Hornik@wu-wien.ac.at> on 1996/05/14

@node Audio Processing
@chapter Audio Processing

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, @emph{linear encoding} and @emph{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
@file{/pub/usenet/news.answers/audio-fmts} of the archive site
@code{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 @file{lin} or @file{raw}, and that
files holding data in mu-law encoding end in @file{au}, @file{mu}, or
@file{snd}.

@anchor{doc-lin2mu}
@deftypefn {Function File} {} lin2mu (@var{x}, @var{n})
Converts audio data from linear to mu-law.  Mu-law values use 8-bit
unsigned integers.  Linear values use @var{n}-bit signed integers or 
floating point values in the range -1<=@var{x}<=1 if @var{n} is 0.  
If @var{n} is not specified it defaults to 0, 8 or 16 depending on 
the range values in @var{x}.
@seealso{mu2lin, loadaudio, saveaudio, playaudio, setaudio, record}
@end deftypefn


@anchor{doc-mu2lin}
@deftypefn {Function File} {} mu2lin (@var{x}, @var{bps})
Converts audio data from linear to mu-law.  Mu-law values are 8-bit
unsigned integers.  Linear values use @var{n}-bit signed integers
or floating point values in the range -1<=y<=1 if @var{n} is 0.  If
@var{n} is not specified it defaults to 8.
@seealso{lin2mu, loadaudio, saveaudio, playaudio, setaudio, record}
@end deftypefn


@anchor{doc-loadaudio}
@deftypefn {Function File} {} loadaudio (@var{name}, @var{ext}, @var{bps})
Loads audio data from the file @file{@var{name}.@var{ext}} into the
vector @var{x}.

The extension @var{ext} determines how the data in the audio file is
interpreted;  the extensions @file{lin} (default) and @file{raw}
correspond to linear, the extensions @file{au}, @file{mu}, or @file{snd}
to mu-law encoding.

The argument @var{bps} can be either 8 (default) or 16, and specifies
the number of bits per sample used in the audio file.
@seealso{lin2mu, mu2lin, saveaudio, playaudio, setaudio, record}
@end deftypefn


@anchor{doc-saveaudio}
@deftypefn {Function File} {} saveaudio (@var{name}, @var{x}, @var{ext}, @var{bps})
Saves a vector @var{x} of audio data to the file
@file{@var{name}.@var{ext}}.  The optional parameters @var{ext} and
@var{bps} determine the encoding and the number of bits per sample used
in the audio file (see @code{loadaudio});  defaults are @file{lin} and
8, respectively.
@seealso{lin2mu, mu2lin, loadaudio, playaudio, setaudio, record}
@end deftypefn


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
@file{/dev/dsp}, and that similarly @file{/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.

@anchor{doc-playaudio}
@deftypefn {Function File} {} playaudio (@var{name}, @var{ext})
@deftypefnx {Function File} {} playaudio (@var{x})
Plays the audio file @file{@var{name}.@var{ext}} or the audio data
stored in the vector @var{x}.
@seealso{lin2mu, mu2lin, loadaudio, saveaudio, setaudio, record}
@end deftypefn


@anchor{doc-record}
@deftypefn {Function File} {} record (@var{sec}, @var{sampling_rate})
Records @var{sec} seconds of audio input into the vector @var{x}.  The
default value for @var{sampling_rate} is 8000 samples per second, or
8kHz.  The program waits until the user types @key{RET} and then
immediately starts to record.
@seealso{lin2mu, mu2lin, loadaudio, saveaudio, playaudio, setaudio}
@end deftypefn


@anchor{doc-setaudio}
@deftypefn {Function File} {} setaudio ([@var{w_type} [, @var{value}]])
Execute the shell command @samp{mixer [@var{w_type} [, @var{value}]]}
@end deftypefn


@anchor{doc-wavread}
@deftypefn {Function File} {@var{y} =} wavread (@var{filename})
Load the RIFF/WAVE sound file @var{filename}, and return the samples
in vector @var{y}.  If the file contains multichannel data, then
@var{y} is a matrix with the channels represented as columns.

@deftypefnx {Function File} {[@var{y}, @var{Fs}, @var{bits}] =} wavread (@var{filename})
Additionally return the sample rate (@var{fs}) in Hz and the number of bits 
per sample (@var{bits}).

@deftypefnx {Function File} {[@dots{}] =} wavread (@var{filename}, @var{n})
Read only the first @var{n} samples from each channel.

@deftypefnx {Function File} {[@dots{}] =} wavread (@var{filename},[@var{n1} @var{n2}])
Read only samples @var{n1} through @var{n2} from each channel.

@deftypefnx {Function File} {[@var{samples}, @var{channels}] =} wavread (@var{filename}, "size")
Return the number of samples (@var{n}) and channels (@var{ch})
instead of the audio data.
@seealso{wavwrite}
@end deftypefn


@anchor{doc-wavwrite}
@deftypefn {Function File} {} wavwrite (@var{y}, @var{filename})
@deftypefnx {Function File} {} wavwrite (@var{y}, @var{fs}, @var{filename})
@deftypefnx {Function File} {} wavwrite (@var{y}, @var{fs}, @var{bits}, @var{filename})
Write @var{y} to the canonical RIFF/WAVE sound file @var{filename}
with sample rate @var{fs} and bits per sample @var{bits}.  The
default sample rate is 8000 Hz with 16-bits per sample.  Each column
of the data represents a separate channel.
@seealso{wavread}
@end deftypefn

