Digital audio processing system and method
View Patent ↗A digital audio processing system and method is disclosed. In an embodiment, the digital audio processing system can include a phase detector to sample an input signal and provide an output to adjust a decimation rate of an input signal. In another embodiment, the digital audio processing system can include symbol recognition logic to determine a symbol using a difference between a nearest predetermined phase value to a sample and a nearest predetermined phase value to a prior sample.
1. A digital audio processing system comprising:
a decimator to perform variable rate decimation of an input signal;
a filter path providing a filtered output of the decimator, the filtered output including a pilot signal having a pilot signal frequency, the filtered output having a sample rate that is approximately an integer multiple of the pilot signal frequency, the integer multiple not less than two and not more than sixty-four;
a phase detector responsive to the filter path and including logic to sample the filtered output; and
wherein an output of the phase detector is coupled to the decimator to adjust a decimation rate of the decimator based on the pilot signal.
2. The digital audio processing system of claim 1 , wherein the integer multiple is four.
3. The digital audio processing system of claim 1 , wherein the integer multiple is thirty-two.
4. The digital audio processing system of claim 1 , wherein the decimator is a variable rate, fractional decimator.
5. The digital audio processing system of claim 1 , wherein the filter path comprises:
an absolute value circuit to provide a first absolute value of a first signal and to provide a second absolute value of a second signal;
a summer coupled to the absolute value circuit to provide a sum of the first absolute value of the first signal and the second absolute value of the second signal; and
a bandpass filter coupled to an output of the summer and configured to pass a band of frequencies that includes the pilot signal frequency.
6. The digital audio processing system of claim 5 , wherein the input signal includes a Near Instantaneous Companded Audio Multiplex (NICAM) signal.
7. The digital audio processing system of claim 6 , wherein the decimator includes a first decimation component to receive an Inphase (I) signal and further includes a second decimation component to receive a Quadrature (Q) signal.
8. A digital audio processing system comprising:
a decimator to perform variable rate decimation of an input signal;
a filter path providing a filtered output of the decimator;
a phase detector responsive to the filter path and including logic to sample the filtered output at a sample rate, the phase detector further including decimation rate control logic to determine a decimation rate command based on a comparison of a sample of the filtered output to zero; and
wherein an output of the phase detector is coupled to the decimator to adjust the decimation rate of the decimator.
9. The digital audio processing system of claim 8 , wherein the decimation rate command is a command to increase the decimation rate when an error associated with the sample has a negative value.
10. The digital audio processing system of claim 9 , wherein the command to increase the decimation rate has a positive value.
11. The digital audio processing system of claim 8 , wherein the decimation rate command is a command to decrease the decimation rate when an error associated with the sample has a positive value.
12. The digital audio processing system of claim 11 , wherein the command to decrease the decimation rate has a negative value.
13. The digital audio processing system of claim 8 , wherein the decimation rate control logic determines the decimation rate command further based on a comparison of an error associated with the sample to a prior sample of the filtered output.
14. The digital audio processing system of claim 13 , wherein the decimation rate control logic determines the decimation rate command further based on a comparison of a computed error value to a predetermined threshold value, the computed error value based on the comparison of the sample of the filtered output to zero and further based on the comparison of the sample of the filtered output to the prior sample of the filtered output.
15. The digital audio processing system of claim 8 , wherein the input signal includes at least one of a Near Instantaneous Companded Audio Multiplex (NICAM) signal and a Broadcast Television Systems Committee (BTSC) signal.