Digital audio processing system and method

1. A digital audio processing method comprising:

receiving first data corresponding to a first signal sampled at a first sample rate;

decimating the first data to provide a second signal sampled at a second sample rate;

recovering a pilot signal from the second signal;

evaluating the pilot signal to determine an error value, wherein the error value is based on a comparison of a sample of the pilot signal to zero; and

adjusting the second sample rate based on the error value.

2. The method of claim 1 , wherein the error value is based on a value of the sample of the pilot signal and a difference between the value and a prior sample value.

3. The method of claim 1 , wherein the comparison of the sample to zero is performed on every Nth sample of the pilot signal, wherein N is four or thirty-two.

4. The method of claim 1 , further comprising:

adjusting a phase value associated with the second signal by an offset value, the offset value based on a detected error of a prior phase value associated with the second signal;

mapping the adjusted phase value to a nearest predetermined phase value selected from a plurality of predetermined phase values; and

outputting an indication of a symbol, wherein the symbol indicates a difference between the nearest predetermined phase value and a prior nearest predetermined phase value.

5. The method of claim 4 , wherein the symbol is a Near Instantaneous Companded Audio Multiplex (NICAM) symbol.

6. The method of claim 4 , wherein the plurality of predetermined phase values includes zero degrees, ninety degrees, one hundred eighty degrees, and two hundred seventy degrees.

7. The method of claim 6 , further comprising:

determining a phase difference between the adjusted phase value and the nearest predetermined phase value; and

modifying the offset value based on the phase difference.

8. A method, comprising:

decimating an input signal at a sample rate to produce first output;

filtering the first output to recover a pilot signal;

evaluating the pilot signal to determine an error value, wherein the error value is based on a comparison of a sample of the pilot signal to zero; and

adjusting the sample rate based on the error value.

9. The method of claim 8 , wherein the error value is based on a value of the sample of the pilot signal and a difference between the value and a prior sample value.

10. The method of claim 8 , wherein the comparison of the sample of the pilot signal to zero is performed on every Nth sample of the pilot signal, wherein N is four or thirty-two.

11. The method of claim 8 , further comprising:

adjusting a phase value associated with the first output by an offset value, the offset value based on a detected error of a prior phase value associated with the first output;

mapping the adjusted phase value to a nearest predetermined phase value selected from a plurality of predetermined phase values; and

outputting an indication of a symbol, wherein the symbol indicates a difference between the nearest predetermined phase value and a prior nearest predetermined phase value.

12. The method of claim 11 , further comprising:

determining a phase difference between the adjusted phase value and the nearest predetermined phase value; and

modifying the offset value based on the phase difference.

13. The method of claim 11 , wherein the symbol is a Near Instantaneous Companded Audio Multiplex (NICAM) symbol.

14. A method, comprising:

decimating a first inphase signal and a first quadrature signal at a sample rate with a decimator to output a second inphase signal and a second quadrature signal;

recovering a pilot signal from the second inphase signal and the second quadrature signal with a pilot filter;

evaluating the pilot signal to determine an error value with a phase detector, wherein the error value is based on a comparison of a sample of the pilot signal to zero; and

adjusting the sample rate at the decimator based on the error value.

15. The method of claim 14 , wherein the first inphase signal and the first quadrature signal are output of a coordinate rotation digital computer mixer.

16. The method of claim 15 , wherein input to the coordinate rotation digital computer mixer comprises an input signal and an input frequency.

17. The method of claim 16 , wherein the input signal is a modulated digital signal.

18. The method of claim 14 , wherein the second inphase signal and the second quadrature signal pass through a channel filter to the pilot filter.

19. The method of claim 14 , wherein the second inphase signal and the second quadrature signal pass through a channel filter to a demodulator.

20. The method of claim 14 , wherein the pilot filter comprises an absolute value circuit and a summer.