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<th nowrap width="1%" height="32">P0030</th>
<th nowrap width="98%">ReadAIFF</th>
<th nowrap width="1%">19th November 1999</th>
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<p><b>Author:</b> Paul G. Lever, Andrew Dodd
<b>Version:</b> 1.1
<b>Path:</b> iac_proj/rd_aiff/</p>
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<h1>ReadAiffData</h1>
<h3>Synopsis</h3>
<p>Reads in an AIFF file and outputs the data as a short
array.</p>
<p>
<hr>
<pre>
module ReadAiffData <src_file="readaiff.cxx",
cxx_src_files="libaiff.cxx"> {
ReadAiffParams+IPort2 &parameters;
cxxmethod+notify_inst+req update;
string+read+notify+req file_name => parameters.file_name;
int+write Num_channels => parameters.Num_channels;
int+write Sample_size => parameters.Sample_size;
int+write Num_samples => parameters.Num_samples;
double+write Sample_rate => parameters.Sample_rate;
short+write+OPort2 out_data[Num_samples];
};
</pre>
<hr>
</p>
<h3>Description</h3>
<p>ReadAiffData reads in an uncompressed AIFF file and outputs an
array of short values representing the samples that make up the waveform. The
amplitude of the samples is represented by a single short value, where 0 is
silence, and 32767 and -32768 represent the extensions of the speaker toward
and away from the listener. It also sets a number of parameters within the
parameter block it references. These describe the format of the sample that it
has loaded. This module is not able to read compressed AIFF audio files and
will give an error message if this is tried.</p>
<h3>Inputs</h3>
<p><b><i>&ReadAiffParams</i></b></p>
<p>Reference to the parameter block, which contains real
instances of the parameters for the ReadAiffData
function.</p>
<p><b><i>file_name</i></b></p>
<p>Name of the AIFF file to be loaded. The parameter is
of type string. This is the only input parameter to the
ReadAiffData function, all the other parameter are set by the
ReadAiffData function. Normally the value of this parameter is
found by referring to the parameter block, which is referenced by
the &ReadAiffParams input.</p>
<h3>Outputs</h3>
<p><b><i>out_data</i></b></p>
<p>The output array containing the waveform contained in the AIFF
file. The array is of type short and uses two bytes to store the amplitude of
each sample, where 0 is quiet, and 32767 and -32768 represent the extensions of
the speaker toward and away from the listener. If the input audio has a sample
size of 8 bits then each byte is expanded so that it fills the full range of
values.</p>
<p><b><i>Num_Channels</i></b></p>
<p>Number of Channels present in AIFF file. The
parameter is of type int, and is set by the ReadAiffData module.
Setting this value has no affect upon the ReadAiffData module.
Normally the value of this parameter is found by referring to the
parameter block, which is referenced by the &ReadAiffParams
input.</p>
<p><b><i>Sample_Size</i></b></p>
<p>Size of each individual sample in bits. The
ReadAiffData module can only cope with sample sizes of either 8
or 16 bits. The parameter is of type int, and is set by the
ReadAiffData module. Setting this value has no affect upon the
ReadAiffData module. Normally the value of this parameter is
found by referring to the parameter block, which is referenced by
the &ReadAiffParams input.</p>
<p><b><i>Num_Samples</i></b></p>
<p>Number of individual samples in the AIFF file. The
parameter is of type int, and is set by the ReadAiffData module.
Setting this value has no affect upon the ReadAiffData module.
Normally the value of this parameter is found by referring to the
parameter block, which is referenced by the &ReadAiffParams
input.</p>
<p><b><i>Sample_Rate</i></b></p>
<p>Number of samples per second. The parameter is of
type double, and is set by the ReadAiffData module. Setting this
value has no affect upon the ReadAiffData module. Normally the
value of this parameter is found by referring to the parameter
block, which is referenced by the &ReadAiffParams
input.</p>
<h3>Utility Macros</h3>
<p>The low-level ReadAiffData module is used in the
Functional Macro ReadAiff and the User Macro readAiff.
Additionally, this macro also uses the ReadAiffParams parameter
block group object, as does the ReadAiffUI UI Macro.</p>
<h3>Example</h3>
<p>An example application ReadAiffEg is provided, which
displays AIFF files on screen using the AGGraph set of graphing
components.</p>
<h3>Files</h3>
<p><i>iac_proj/rd_aiff/aiffmods.v</i> contains the
ReadAiffParams group and the ReadAiffData module V
definitions.</p>
<h3>Other Notes</h3>
<p>The low-level ReadAiffMods library containing the
module ReadAiffData does not specify a process. By default the
<tt>express</tt> process will be used.</p>
<h3>Authors</h3>
<pre>
Paul G. Lever
Andrew Dodd
</pre>
<h3>Contact</h3>
<pre>
International AVS Centre
Manchester Visualization Centre
Manchester Computing
University of Manchester
Oxford Road
Manchester
United Kingdom
M13 9PL
</pre>
<h3>See Also</h3>
<p>ReadAiffParams, ReadAiffUI, ReadAiff, readAiff</p>
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