72 lines
3.1 KiB
Markdown
72 lines
3.1 KiB
Markdown
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layout: page
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---
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# libsndfile and GNU Octave
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[GNU Octave](http://www.octave.org/) is a high-level interactive language for
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numerical computations. There are currently two development streams, a stable
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2.0.X series and a development 2.1.X series. Octave reads and writes data in
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binary formats that were originally developed for
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[MATLAB](http://www.mathworks.com/). Version 2.0.X of Octave uses binary data
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files compatible with MATLAB version 4.2 while Octave 2.1.X uses binary data
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files compatible with MATLAB version 5.0 as well as being able to read the older
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MATLAB 4.2 format.
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From version 1.0.1 of libsndfile onwards, libsndfile has the ability of reading
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and writing a small subset of the binary data files used by both versions of GNU
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Octave. This gives people using GNU Octave for audio based work an easy method
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of moving audio data between GNU Octave and other programs which use libsndfile.
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For instance it is now possible to do the following:
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* Load a WAV file into a sound file editor such as
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[Sweep](http://www.metadecks.org/software/sweep/).
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* Save it as a MAT4 file.
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* Load the data into Octave for manipulation.
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* Save the modified data.
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* Reload it in Sweep.
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Another example would be using the MAT4 or MAT5 file formats as a format which
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can be easily loaded into Octave for viewing/analyzing as well as a format which
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can be played with command line players such as the one included with
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libsndfile.
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## Details
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Octave, like most programming languages, uses variables to store data, and
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Octave variables can contain both arrays and matrices. It is also able to store
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one or more of these variables in a file. When reading Octave files, libsndfile
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expects a file to contain two variables and their associated data. The first
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variable should contain a variable holding the file sample rate while the second
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variable contains the audio data.
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For example, to generate a sine wave and store it as a binary file which is
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compatible with libsndfile, do the following:
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octave:1 > samplerate = 44100 ;
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octave:2 > wavedata = sin ((0:1023)*2*pi/1024) ;
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octave:3 > save sine.mat samplerate wavedata
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The process of reading and writing files compatible with libsndfile can be made
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easier by use of two Octave script files:
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octave:4 > [data fs] = sndfile_load ("sine.mat") ;
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octave:5 > sndfile_save ("sine2.mat", data, fs) ;
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In addition, libsndfile contains a command line program which which is able to
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play the correct types of Octave files. Using this command line player
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**sndfile-play** and a third Octave script file allows Octave data to be played
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from within Octave on any of the platforms which **sndfile-play** supports (at
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the moment: Linux, MacOS X, Solaris and Win32).
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octave:6 > sndfile_play (data, fs) ;
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These three Octave scripts are installed automatically in Octave's site script
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directory when libsndfile is installed (except on Win32) ie when libsndfile is
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being installed into /usr/local, the Octave scripts will be installed in
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/usr/local/share/octave/site/m/.
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There are some other Octave scripts for audio to be found
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[here](http://octave.sourceforge.net/audio/index.html).
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