Sample rate converter with automatic anti-aliasing filter
AssigneeMicrosoft Technology Licensing, LLC
InventorThomas Craig Savell
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Abstract
The subject disclosure is directed towards dynamically computing anti-aliasing filter coefficients for sample rate conversion in digital audio. In one aspect, for each input-to-output sampling rate ratio (pitch) obtained, anti-aliasing filter coefficients are interpolated based upon the pitch (e.g., using the fractional part of the ratio) from two filters (coefficient sets) selected based upon the pitch (e.g., using the integer part of the ratio). The interpolation provides for fine-grained cutoff frequencies, and by re-computation for each pitch, smooth anti-aliasing with dynamically changing ratios.
Claims20
A method comprising:
- obtaining a pitch corresponding to an input audio sampling rate of an input sample and an output audio rate for a sample rate converted sample;
- selecting one filter comprising one set of coefficient values based upon the pitch;
- selecting another filter comprising another set of coefficient values based upon the pitch;
- obtaining a resultant set of pitch-based coefficient values-by interpolating between the one set of coefficient values corresponding to the one filter and the other set of coefficient values corresponding to the other filter;
- and
- filtering data corresponding to the input sample to provide for anti-aliasing of the sampling rate converted sample for output using the resultant set of pitch-based coefficient values.
A system comprising:
- a sample rate conversion component configured to:
- convert an input sample into audio output based upon a specified pitch value, the sample rate conversion component coupled to a coefficient lookup table and further configured to obtain a pitch value;
- automatically read a plurality of sets of filtering coefficients from the coefficient lookup table set based upon at least part of the pitch value;
- and
- based upon at least part of the pitch value, automatically interpolate the sets of filtering coefficients into anti-aliasing filtering coefficients for use by a digital audio filter.
One or more computer-readable storage devices having computer-executable instructions that cause the one or more processor to perform operations comprising:
- accessing audio data corresponding to an input sample;
- obtaining, as a current pitch value, a value corresponding to a ratio of an input sampling rate of the input sample to an output sampling rate for outputting a converted output of the input sample;
- interpolating between filter coefficient sets based upon the current pitch value to obtain a filtering coefficient set;
- performing anti-aliasing filtering using the filtering coefficient set;
- outputting a first set of audio data corresponding to the converted output after performing anti-aliasing filtering;
- obtaining, as the current pitch value, a changed pitch value corresponding to a changed ratio of the input sampling rate of the input sample to the output sampling rate for outputting a converted output of the input sample;
- interpolating between the filter coefficient sets based upon the changed pitch value to obtain a second filtering coefficient set;
- performing anti-aliasing filtering using the second filtering coefficient set;
- and
- outputting a second set of audio data corresponding to the converted output after performing anti-aliasing filtering using the second filtering coefficient set.
Dependencies are inferred from the claim text.