On Sep 24, 2008, at 8:54 AM, Evan Olcott wrote:
A technical question (asking this in order to do a certain kind of analysis) -
Are there any of the AudioConvertor settings that would use a "windowed sinc interpolation" for the conversion?
Windowed sinc interpolation is the default setting.
There are two relevant settings.
One is kAudioConverterSampleRateConverterComplexity
There are three values for this setting:
kAudioConverterSampleRateConverterComplexity_Linear
linear interpolation. not what you want. This is for use when speed is crucial.
kAudioConverterSampleRateConverterComplexity_Normal
windowed sinc function. This is the default.
kAudioConverterSampleRateConverterComplexity_Mastering
windowed sinc function with larger windows. Mastering gives a higher range of quality than Normal.
The quality setting, kAudioConverterSampleRateConverterQuality, controls the number of points of the windowed sinc function.
For Normal complexity the quality settings are as follows:
Min - 16 points.
Low - 16 points.
Med - 32 points.
High - 64 points.
Max - 96 points.
For Mastering complexity the quality settings are as follows:
Min - 128 points.
Low - 256 points.
Med - 512 points.
High - 1024 points.
Max - 2048 points.
In addition, the quality setting adjusts cutoff frequency and stopband attenuation to get the best result for the particular filter length.