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Add test to determine if the sample rate conversion ratio is a power of 2. 

If so, use linear interpolation.  Otherwise use more complicated quadratic
interpolation which tends to sound terrible, but is better than trying to
use linear for a non-standard conversion.
This commit is contained in:
jbebel 2005-04-03 05:18:24 +00:00
parent 57b6c729ee
commit 806550e495
1 changed files with 29 additions and 2 deletions
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31
darkice/trunk/src/VorbisLibEncoder.cpp
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@ -87,11 +87,32 @@ VorbisLibEncoder :: init ( CastSink * sink,
} else {
resampleRatio = ( (double) getOutSampleRate() /
(double) getInSampleRate() );
// Determine if we can use linear interpolation.
// The inverse of the ratio must be a power of two for linear mode to
// be of sufficient quality.
bool useLinear = true;
double inverse = 1 / resampleRatio;
int integer = inverse;
if( integer == inverse ) { // Check that the inverse of the ratio is an integer
while( useLinear && integer ) { // Loop through the bits
if( integer & 1 && integer != 1 ) // If the lowest order bit is not the only one set
useLinear = false; // Not a power of two; cannot use linear
else
integer >>= 1; // Shift all the bits over and try again
}
} else
useLinear = false;
// If we get here and useLinear is still true, then we have a power of two.
// open the aflibConverter in
// - high quality
// - not linear (quadratic) interpolation
// - linear or quadratic (non-linear) based on algorithm
// - not filter interpolation
converter = new aflibConverter( true, true, false);
converter = new aflibConverter( true, useLinear, false);
}
encoderOpen = false;
@ -387,6 +408,12 @@ VorbisLibEncoder :: close ( void ) throw ( Exception )
$Source$
$Log$
Revision 1.20 2005/04/03 05:18:24 jbebel
Add test to determine if the sample rate conversion ratio is a power of 2.
If so, use linear interpolation. Otherwise use more complicated quadratic
interpolation which tends to sound terrible, but is better than trying to
use linear for a non-standard conversion.
Revision 1.19 2004/03/13 10:41:39 darkeye
added possibility to downsample from stereo to mono when encoding
to Ogg Vorbis