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118 lines
3.9 KiB
HTML
118 lines
3.9 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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libsndfile and GNU Octave
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</TITLE>
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<META NAME="Author" CONTENT="Erik de Castro Lopo (erikd AT mega-nerd DOT com)">
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<LINK REL=StyleSheet HREF="libsndfile.css" TYPE="text/css" MEDIA="all">
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</HEAD>
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<BODY>
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<BR>
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<H1><B>libsndfile and GNU Octave</B></H1>
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<P>
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<A HREF="http://www.octave.org/">GNU Octave</A> is a high-level interactive
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language for numerical computations.
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There are currently two development streams, a stable 2.0.X series and a
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development 2.1.X series.
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Octave reads and writes data in binary formats that were originally developed
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for
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<A HREF="http://www.mathworks.com/">MATLAB</A>.
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Version 2.0.X of Octave uses binary data files compatible with MATLAB
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version 4.2 while Octave 2.1.X uses binary data files compatible
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with MATLAB version 5.0 as well as being able to read the older MATLAB 4.2
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format.
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</P>
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<P>
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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
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of GNU Octave.
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This gives people using GNU Octave for audio based work an easy method of
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moving audio data between GNU Octave and other programs which use libsndfile.
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</P>
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<P>
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For instance it is now possible to do the following:
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</P>
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<UL>
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<LI> Load a WAV file into a sound file editor such as
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<A HREF="http://www.metadecks.org/software/sweep/">Sweep</A>.
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<LI> Save it as a MAT4 file.
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<LI> Load the data into Octave for manipulation.
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<LI> Save the modified data.
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<LI> Reload it in Sweep.
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</UL>
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<P>
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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
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which can be played with command line players such as the one included with
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libsndfile.
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</P>
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<H2><B>Details</B></H2>
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<P>
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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.
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It is also able to store one or more of these variables in a file.
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When reading Octave files, libsndfile expects a file to contain two
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variables and their associated data.
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The first variable should contain a variable holding the file sample rate
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while the second variable contains the audio data.
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</P>
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<P>
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For example, to generate a sine wave and store it as a binary file which
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is compatible with libsndfile, do the following:
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</P>
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<PRE>
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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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</PRE>
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<P>
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The process of reading and writing files compatible with libsndfile can be
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made easier by use of two Octave script files :
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</P>
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<PRE>
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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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</PRE>
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<P>
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In addition, libsndfile contains a command line program which which is able
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to play the correct types of Octave files.
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Using this command line player <B>sndfile-play</B> and a third Octave script
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file allows Octave data to be played from within Octave on any of the platforms
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which <B>sndfile-play</B> supports (at the moment: Linux, MacOSX, Solaris and
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Win32).
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</P>
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<PRE>
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octave:6 > sndfile_play (data, fs) ;
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</PRE>
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<P>
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These three Octave scripts are installed automatically in Octave's site
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script directory when libsndfile is installed (except on Win32) ie when
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libsndfile is being installed into /usr/local, the Octave scripts will
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be installed in /usr/local/share/octave/site/m/.
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</P>
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<P>
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There are some other Octave scripts for audio to be found
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<A HREF="http://octave.sourceforge.net/index/audio.html">here</A>.
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</P>
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<BR>
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<!-- ========================================================================= -->
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<HR>
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<P>
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The libsndfile home page is here :
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<A HREF="http://www.mega-nerd.com/libsndfile/">
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http://www.mega-nerd.com/libsndfile/</A>.
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</P>
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