Asynchronous sample rate conversion using a digital simulation of an analog filter
AssigneeDolby Laboratories Licensing Corporation
InventorDavid Stanley McGrath
Life of this patent
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Abstract
The sample rate of a digital signal is converted by a digital simulation of an analog filter. The simulation can update the states of complex poles in the analog filter at arbitrary times using different techniques. One technique updates the states at variable rates. Other techniques update the states at a fixed rate in response to values of input or output samples that are modified to account for offsets between the times of the samples and the times the states are updated. The states may be updated by using interpolations of complex exponential functions. Values of the complex exponential functions may be obtained from a product of values obtained from multiple lookup tables.
Claims18
A method for sample rate conversion that comprises:
- receiving source digital samples that represent a source electrical signal at a source sample rate;
- generating destination digital samples by applying to the source digital samples a digital simulation of an analog filter that has an infinite impulse response, wherein the destination digital samples represent the source electrical signal at a destination sample rate that differs from the source sample rate, wherein the digital simulation simulates states of complex poles in the analog filter in a manner that reflects the states of the complex poles as being updated in response to values that are obtained from an interpolation of complex exponential functions and at rates that are variable, wherein values of the complex exponential functions are obtained by calculating products of values retrieved from lookup tables based on exponents of varying resolution;
- and
- transmitting the destination digital samples.
An apparatus for sample rate conversion that comprises:
- an input terminal that receives source digital samples that represent a source electrical signal at a source sample rate;
- circuitry coupled to the input terminal that provides a digital simulation of states of complex poles in an analog filter that has an infinite impulse response, wherein the circuitry generates destination digital samples that represent the source electrical signal at a destination sample rate that differs from the source sample rate by applying the digital simulation to the source digital samples as if the states of the complex poles are updated in response to values that are obtained from an interpolation of complex exponential functions and at rates that are variable, wherein the circuitry obtains values of the complex exponential functions by calculating products of values retrieved from lookup tables based on exponents of varying resolution;
- and
- an output terminal coupled to the circuitry that transmits the destination digital samples.
A computer-readable storage medium recording a program of instructions that is executable by a device to perform a method for sample rate conversion, wherein the method comprises:
- receiving source digital samples that represent a source electrical signal at a source sample rate;
- generating destination digital samples by applying to the source digital samples a digital simulation of an analog filter that has an infinite impulse response, wherein the destination digital samples represent the source electrical signal at a destination sample rate that differs from the source sample rate, wherein the digital simulation simulates states of complex poles in the analog filter in a manner that reflects the states of the complex poles as being updated in response to values that are obtained from an interpolation of complex exponential functions and at rates that are variable, wherein values of the complex exponential functions are obtained by calculating products of values retrieved from lookup tables based on exponents of varying resolution;
- and
- transmitting the destination digital samples.
Dependencies are inferred from the claim text.