PSYCHOACOUSTIC FILTER DESIGN FOR RATIONAL RESAMPLERS
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Abstract
The present document relates to the design of anti-aliasing and/or anti-imaging filters for resamplers using rational resampling factors. In particular, the present document relates to a method for designing such filters having a reduced number of filter coefficients or an increased perceptual performance, as well as to the filters designed using such method. A method for designing a filter (102) configured to reduce imaging and/or aliasing of an output audio signal (113) at an output sampling rate (fsout) is described. The output audio signal (113) is a resampled version of an input audio signal (110) at an input sampling rate (fsin). The ratio of the output sampling rate (fsout) and the input sampling rate (fsin) is a rational number N/M. The filter (102) operates at an upsampled sampling rate which equals N times the input sampling rate (fsin). The method comprises the steps of selecting an allowed deviation of the frequency response (531, 532) of the filter (102) within a stop band of the filter (102) based on a perceptual frequency response indicative of an auditory spectral sensitivity; wherein the allowed deviation indicates a deviation of the frequency response (531, 532) of the filter (102) from a predetermined attenuation within the stop band; and of determining coefficients of the filter (102) such that the frequency response (531, 532) of the filter (102) is fitted to the allowed deviation of the frequency response (531, 532).
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Citations
56 Claims
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1-34. -34. (canceled)
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35. A method for designing a filter configured to reduce imaging and/or aliasing of an output audio signal at an output sampling rate;
- wherein the output audio signal is a resampled version of an input audio signal at an input sampling rate;
wherein the ratio of the output sampling rate and the input sampling rate is a rational number N/M; wherein the filter operates at an upsampled sampling rate which equals N times the input sampling rate; the method comprising selecting an allowed deviation of the frequency response of the filter within a stop band of the filter based on a perceptual frequency response indicative of an auditory spectral sensitivity;
wherein the allowed deviation indicates a deviation of the frequency response of the filter from a predetermined attenuation within the stop band;the step of selecting the allowed deviation of the frequency response of the filter within the stop band comprising the step of partitioning the stop band into a plurality of frequency intervals comprising one or more “
don'"'"'t care”
intervals and one or more “
care”
intervals;in the one or more “
don'"'"'t care”
intervals, the components of the input audio signal providing no contribution to the frequency components of the output audio signal;the allowed deviation of the frequency response taking on arbitrary or undefined values within the one or more “
don'"'"'t care”
intervals and being unconstrained or undefined within the one or more “
don'"'"'t care”
intervals;in the one or more “
care”
intervals, the frequency response of the filter taking on a pre-determined form;the perceptual frequency response being associated with a first perceptual frequency response indicative of a scaled and/or mirrored absolute threshold of hearing curve; the allowed deviation of the frequency response within the one or more “
care”
intervals being derived from the absolute threshold of hearing curve; anddetermining coefficients of the filter such that the frequency response of the filter is fitted to the allowed deviation of the frequency response; the step of determining coefficients of the filter comprising fitting the frequency response of the filter to the allowed deviation of the frequency response outside of the one or more “
don'"'"'t care”
intervals;
while imposing no constraints on the frequency response of the filter within the one or more “
don'"'"'t care”
intervals. - View Dependent Claims (36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 55)
- wherein the output audio signal is a resampled version of an input audio signal at an input sampling rate;
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48. A filter configured to reduce imaging and/or aliasing of an output audio signal at an output sampling rate;
- wherein
the output audio signal is a resampled version of an input audio signal at an input sampling rate; the ratio of the output sampling rate and the input sampling rate is a rational number N/M; the filter operates at an upsampled sampling rate which equals N times the input sampling rate; the filter comprises a pass band and a stop band; a frequency response of the filter within the stop band is associated with a perceptual frequency response indicative of an auditory spectral sensitivity; the frequency response of the filter within the stop band being selected by partitioning the stop band into a plurality of frequency intervals comprising one or more “
don'"'"'t care”
intervals and one or more “
care”
intervals;in the one or more “
don'"'"'t care”
intervals, the components of the input audio signal providing no contribution to the frequency components of the output audio signal;the frequency response taking on arbitrary or undefined values within the one or more “
don'"'"'t care”
intervals and being unconstrained or undefined within the one or more “
don'"'"'t care”
intervals;in the one or more “
care”
intervals, the frequency response of the filter taking on a pre-determined form;the perceptual frequency response being associated with a first perceptual frequency response indicative of a scaled and/or mirrored absolute threshold of hearing curve; the frequency response within the one or more “
care”
intervals being derived from the absolute threshold of hearing curve. - View Dependent Claims (49, 50, 51)
- wherein
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52. A method for resampling an input audio signal at an input sampling rate to an output audio signal at an output sampling rate;
- wherein the ratio of the output sampling rate and the input sampling rate is a rational number N/M;
the method comprising;providing a set of coefficients of a filter, wherein the filter operates at an upsampled sampling rate which equals N times the input sampling rate; the filter comprises a pass band and a stop band; a frequency response of the filter within the stop band is associated with a perceptual frequency response indicative of an auditory spectral sensitivity; the frequency response of the filter within the stop band being selected by partitioning the stop band into a plurality of frequency intervals comprising one or more “
don'"'"'t care”
intervals and one or more “
care”
intervals;in the one or more “
don'"'"'t care”
intervals, the components of the input audio signal providing no contribution to the frequency components of the output audio signal;the frequency response taking on arbitrary or undefined values within the one or more “
don'"'"'t care”
intervals and being unconstrained or undefined within the one or more “
don'"'"'t care”
intervals;in the one or more “
care”
intervals, the frequency response of the filter taking on a pre-determined form;the perceptual frequency response being associated with a first perceptual frequency response indicative of a scaled and/or mirrored absolute threshold of hearing curve; and the frequency response within the one or more “
care”
intervals being derived from the absolute threshold of hearing curve,selecting a first subset of coefficients from the set of coefficients;
wherein the first subset comprises a first coefficient of the set and coefficients of the set following the first coefficient by multiples of N; anddetermining a first sample of the output audio signal based on the first subset of coefficients and a first plurality of samples of the input audio signal. - View Dependent Claims (53, 56)
- wherein the ratio of the output sampling rate and the input sampling rate is a rational number N/M;
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54. A resampler configured to generate an output audio signal at an output sampling rate from an input audio signal at an input sampling rate;
- wherein the ratio of the output sampling rate and the input sampling rate is a rational number N/M;
the resampler comprising;a filter having a set of coefficients, wherein the filter operates at an upsampled sampling rate which equals N times the input sampling rate; the filter comprises a pass band and a stop band; a frequency response of the filter within the stop band is associated with a perceptual frequency response indicative of an auditory spectral sensitivity; the frequency response of the filter within the stop band being selected by partitioning the stop band into a plurality of frequency intervals comprising one or more “
don'"'"'t care”
intervals and one or more “
care”
intervals;in the one or more “
don'"'"'t care”
intervals, the components of the input audio signal providing no contribution to the frequency components of the output audio signal;the frequency response taking on arbitrary or undefined values within the one or more “
don'"'"'t care”
intervals and being unconstrained or undefined within the one or more “
don'"'"'t care”
intervals;in the one or more “
care”
intervals, the frequency response of the filter taking on a pre-determined form;the perceptual frequency response being associated with a first perceptual frequency response indicative of a scaled and/or mirrored absolute threshold of hearing curve; and the frequency response within the one or more “
care”
intervals being derived from the absolute threshold of hearing curve,a coefficient selection unit configured to select a subset of coefficients from the set of coefficients; and a filtering unit configured to generate a sample of the output audio signal from a plurality of samples of the input audio signal using the subset of coefficients.
- wherein the ratio of the output sampling rate and the input sampling rate is a rational number N/M;
Specification