Asynchronous sample rate converter
AssigneeCirrus Logic, Inc.
InventorsJohn Paulos, Gautham Kamath, James Nohrden
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Abstract
An asynchronous sample rate converter for converting a first sample rate in a signal to a second sample rate in the same signal is presented. The signal is first provided as input to an interpolator which upsamples the signal to form a signal having sample rate UFs1 where the upsampling factor U is a variable that is directly related to the ratio Fs2/Fs1. The resampler then linearly interpolates the upsampled signal to form a signal having sample rate DFs2. Finally, the resampled signal is downsampled to form a signal having sample rate Fs2.
Claims31
An asynchronous sample rate converter for converting a first sample rate Fs1 of a signal A to a second sample rate Fs2 comprising:
- an interpolation filter receiving as input the signal A having the first sample rate Fs1, the interpolation filter upsampling the sample rate to a sample rate UFs1, where the upsampling factor U is directly related to a ratio of Fs2/Fs1, the interpolation filter removing images during upsampling, the interpolation filter providing as output a signal B(n) having the upsampled sample rate UFs1;
- a resampler receiving as input the signal B(n) from the interpolation filter, the resampler resampling the signal B(n) to have a sample rate DFs2, where D is a downsampling factor, the resampler performing linear interpolation on the resampled signal, the resampler providing as output the linearly interpolated signal C(n) having the sample rate DFs2 wherein the resampler comprises a linear interpolator circuit that performs linear interpolation on the signal B(n) so that magnitude attenuation zeros are placed in a frequency spectrum of the signal B(n) at integer multiples of the sample rate DFs2;
- and
- a decimation filter receiving as input the linearly interpolated signal having the sample rate DFs2, the decimation filter downsampling the linearly interpolated signal C(n) having the sample rate DFs2 to a signal Z having the second sample rate Fs2.
A digital audio system comprising:
- a drive mechanism unit;
- a plurality of digital signal processors coupled to the drive mechanism unit;
- a central processor coupled to the plurality of digital signal processors;
- a digital audio input/output (I/O) circuit coupled to the digital signal processors, the digital audio I/O circuit having an asynchronous sample rate converter for converting a first sample rate Fs1 of a signal A to a second sample rate Fs2 comprising:
- an interpolation filter receiving as input the signal A having the first sample rate Fs1, the interpolation filter upsampling the sample rate to a sample rate UFs1, where the upsampling factor U is directly related to a ratio of Fs2/Fs1, the interpolation filter removing images during upsampling, the interpolation filter providing as output a signal B(n) having the upsampled sample rate UFs1;
- a resampler receiving as input the signal B(n) from the interpolation filter, the resampler resampling the signal B(n) to have a sample rate DFs2, where D is a downsampling factor, the resampler performing linear interpolation on the resampled signal, the resampler providing as output the linearly interpolated signal C(n) having the sample rate DFs2 wherein the resampler comprises a linear interpolator circuit that performs linear interpolation on the signal B(n) so that magnitude attenuation zeros are placed in a frequency spectrum of the signal B(n) at integer multiples of the sample rate DFs2;
- and
- a decimation filter receiving as input the linearly interpolated signal having the sample rate DFs2, the decimation filter downsampling the linearly interpolated signal C(n) having the sample rate DFs2 to a signal Z having the second sample rate Fs2.
A method for asynchronously converting a first sample rate Fs1 in a signal A into a second sample rate Fs2, the method comprising the steps of:
- a) upsampling and filtering a signal A to form an upsampled signal B(n) having a sample rate UFs1, where the upsampling factor U is directly related to a ratio of Fs2/Fs1;
- b) resampling and linearly interpolating the upsampled signal to form a linearly interpolated signal C(n) having a sample rate DFs2, wherein D is a downsampling factor and wherein magnitude attenuation zeros are placed in a frequency spectrum of the signal B(n) at integer multiples of the sample rate DFs2;
- and
- c) downsampling the resampled signal C(n) to form a signal Z having a sample rate Fs2.
Dependencies are inferred from the claim text.