Method and apparatus for automatic audio alignment in a hybrid radio system

1. A method of processing a digital radio broadcast signal in a digital radio receiver, the method comprising:

(a) determining a plurality of current correlation sample values representative of a time delay between samples in an analog audio sample stream and samples in a digital audio sample stream;

(b) determining a current inversion status between the samples in an analog audio sample stream and samples in a digital audio sample stream;

(c) updating a delay history and an inversion status history;

(d) checking the current correlation sample values for consistency with a first confidence threshold:

(e) determining if each of a first plurality of values in the delay history is consistent within a predetermined range of the current correlation sample values when the consistency is found in step (d);

(f) when the consistency is found in step (e), determining if a value in the inversion status history is consistent with the current inversion status; and

(g) when the consistency is found in step (f), allowing blending of an output to the digital audio sample stream.

2. The method of claim 1 , wherein if the consistency is not found in step (d), then the method further comprises:

(h) checking the current correlation sample values for consistency with a second confidence threshold;

(i) if the consistency is found in step (h), determining if each of a second plurality of values in the delay history is consistent within a predetermined range of the current correlation sample values;

(j) if the consistency is found in step (i), determining if the value in the inversion status history is consistent with the current inversion status; and

(k) if the consistency is found in step (j), allowing blending of the output to the digital audio sample stream.

3. The method of claim 2 , wherein if the consistency is not found in step (h), then the method further comprises:

(I) checking the current. correlation sample values for consistency with a third confidence threshold;

(m) if the consistency is found in step (l), determining if each of a third plurality of values in the delay history is consistent within a predetermined range of the current correlation sample values;

(n) if the consistency is found in step (m), determining if the value in the inversion status history is consistent with the current inversion status; and

(o) if the consistency is found in step (n), allowing blending of the output to the digital audio sample stream.

4. The method of claim 3 , wherein if the consistency is not found in step (k), then the method further comprises:

repeating steps (a), (b), (c), (d), (e), (f) and (g) using different samples in the analog audio sample stream and different samples in the digital audio sample stream.

5. The method of claim 3 , wherein the first confidence threshold is lower than the second confidence threshold, and the second confidence threshold is lower than the third confidence threshold.

6. The method of claim 3 , wherein the first plurality of values in the delay history is smaller than the second plurality of values in the delay history, and the second plurality of values in the delay history is smaller than the third plurality of values in the delay history.

7. The method of claim 1 , wherein the history update is accomplished by copying values from a most recent correlation iteration into a buffer for each of the delay and inversion containing the values from previous iterations up to a maximum configurable history length.

8. The method of claim 7 , wherein an overall history length represents a time history divided into discrete windows defined by a length of a scan range.

9. A receiver for a digital radio broadcast signal, the receiver comprising:

an antenna and a processing circuit, the processing circuit configured to:

(a) determine a plurality of current correlation sample values representative of a time delay between samples in an analog audio sample stream and samples in a digital audio sample stream;

(b) determine a current inversion status between the samples in an analog audio sample stream and samples in a digital audio sample stream;

(c) update a delay history and an inversion status history;

(d) check the current correlation sample values for consistency with a first confidence threshold;

(e) determine if each of a first plurality of values in the delay history is consistent within a predetermined range of the current correlation sample values when the consistency is found in step (d);

(f) when the consistency is found in step (e), determine if a value in the inversion status history is consistent with the current inversion status; and

(g) when the consistency is found in step (f), allow blending of an output to the digital audio sample stream.

10. The receiver of claim 9 , wherein if the consistency is not found in step (d), then the processing circuit is further configured to:

(h) check the current correlation sample values for consistency with a second confidence threshold;

(i) if the consistency is found in step (h), determine if each of a second plurality of values in the delay history is consistent within a predetermined range of the current correlation sample values;

(j) if the consistency is found in step (i), determine if the value in the inversion status history is consistent with the current inversion status; and

(k) if the consistency is found in step (j), allow blending of the output to the digital audio sample stream.

11. The receiver of claim 10 , wherein if the consistency is not found in step (h), then the processing circuit is further configured to:

(l) check the current correlation sample values for consistency with a third confidence threshold;

(m) if the consistency is found in step (l), determine if each of a third plurality of values in the delay history is consistent within a predetermined range of the current correlation sample values;

(n) if the consistency is found in step (m), determine if the value in the inversion status history is consistent with the current inversion status; and

(o) if the consistency is found in step (n), allow blending of the output to the digital audio sample stream.

12. The receiver of claim 11 , wherein if the consistency is not found in step (k), then the processing circuit is further configured to:

repeat steps (a), (b), (c), (d), (e), (f) and (g) using different samples in the analog audio sample stream and different samples in the digital audio sample stream.

13. The receiver of claim 11 , wherein the first confidence threshold is lower than the second confidence threshold, and the second confidence threshold is lower than the third confidence threshold.

14. The receiver of claim 11 , wherein the first plurality of values in the delay history is smaller than the second plurality of values in the delay history, and the second plurality of values in the delay history is smaller than the third plurality of values in the delay history.

15. The receiver of claim 9 , wherein the history update is accomplished by copying values from a most recent correlation iteration into a butler for each of the delay and inversion containing the values from previous iterations up to a maximum configurable history length.

16. The receiver of claim 15 , wherein an overall history length represents a time history divided into discrete windows defined by a length of a scan range.

17. A non-transitory computer readable storage medium containing executable instructions configured to cause a processing system to execute a method comprising:

(a) determining a plurality of current correlation sample values representative of a time delay between samples in an analog audio sample stream and samples in a digital audio sample stream;

(b) determining a current inversion status between the samples in an analog audio sample stream and samples in a digital audio sample stream;

(c) updating a delay history and an inversion status history;

(d) checking the current correlation sample values for consistency with a first confidence threshold;

(e) determining if each of a first plurality of values in the delay history is consistent within a predetermined range of the current correlation sample values when the consistency is found in step (d);

(f) when the consistency found in step (e), determining if a value in the inversion status history is consistent with the current inversion status; and

(g) when the consistency is found in step (f), allowing blending of an output to the digital audio sample stream.

18. The non-transitory computer readable storage medium of claim 17 , further containing executable instructions configured to cause a processing system to execute the steps of:

(h) checking the current correlation sample values for consistency with a second confidence threshold;

(i) if the consistency is found in step (h), determining if each of a second plurality of values in the delay history is consistent within a predetermined range of the current correlation sample values;

(j) if the consistency is found in step (i), determining if the value in the inversion status history is consistent with the current inversion status; and

(k) if the consistency is found in step (j), allowing blending of the output to the digital audio sample stream.

19. The non-transitory computer readable storage medium of claim 18 , further containing executable instructions configured to cause a processing system to execute the steps of:

(l) checking the current correlation sample values for consistency with a third confidence threshold;

(m) if the consistency is found in step (l), determining if each of a third plurality of values in the delay history is consistent within a predetermined range of the current correlation sample values;

(n) if the consistency is found in step (m), determining if the value in the immersion status history is consistent with the current inversion status; and

(o) if the consistency is found in step (n), allowing blending of the output to the digital audio sample stream.

20. The non-transitory computer readable storage medium of claim 19 , further containing executable instructions configured to cause a processing system repeat steps (a), (b), (c), (d), (e), (f) and (g) using different samples in the analog audio sample stream and different samples in the digital audio sample stream.