Time-alignment measurement for hybrid HD radio™ technology

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

receiving a hybrid broadcast signal;

demodulating the hybrid broadcast signal to produce an analog audio stream and a digital audio stream;

using a normalized cross-correlation of envelopes of the analog audio stream and the digital audio stream to measure a time offset between the analog audio stream and the digital audio stream;

blending an output of the radio receiver from the analog audio stream to the digital audio stream or from the digital audio stream to the analog audio stream;

phase-adjusting the digital audio stream; and

using the phase-adjusted digital audio stream to temporarily replace input digital audio frames during blend ramps used in the blending of the output of the radio receiver.

2. The method of claim 1 , further comprising:

using the time offset to align the analog audio stream and the digital audio stream.

3. The method of claim 1 , further comprising:

using the time offset to scale an analog signal blend metric, to control blend thresholds in the blending of the output of the radio receiver, and to inhibit blending when misalignment is detected.

4. The method of claim 1 , further comprising:

computing cross-correlation of bass signals to detect potential inversion, to validate time offset measurements, or to improve blend quality.

5. The method of claim 1 , further comprising:

computing cross-correlation of the analog audio stream and the digital audio stream to predict sound quality of a potential blend.

6. The method of claim 1 , wherein:

the normalized cross-correlation of envelopes is computed using a vector of bandpass samples of the analog audio stream and a vector of bandpass samples of the digital audio stream.

7. The method of claim 1 , wherein the step of using a normalized cross-correlation of envelopes of the analog audio stream and the digital audio stream to measure a time offset between the analog audio stream and the digital audio stream comprises:

using a coarse envelope cross-correlation computed over a first range of lag values to locate a vicinity of the time offset; and

subsequently using a fine envelope cross-correlation computed over a second range of lag values, wherein the second range of lag values is narrower than the first range of lag values.

8. The method of claim 7 , further comprising:

using quadratic interpolation of peak indices to improve resolution of a computed peak lag.

9. The method of claim 1 , wherein

the normalized cross-correlation of envelopes is computed using a vector of samples of the analog audio stream and a vector of samples of the digital audio stream; and

the normalized cross-correlation of envelopes of the vector of samples of the analog audio stream and the vector of samples of the digital audio stream produces bifurcated and composite correlation peaks that are compared for correlation validation via temporal consistency.

10. The method of claim 1 , wherein:

the normalized cross-correlation of envelopes is computed using a vector of samples of the analog audio stream and a vector of samples of the digital audio stream; and

the normalized cross-correlation of envelopes of the analog audio vector and the digital audio vector produces current and previous peaks that are compared for correlation validation via temporal consistency.

11. The method of claim 1 , further comprising:

calculating phase-adjusted frequency-domain correlation coefficients to validate the time offset.

12. A radio receiver comprising:

processing circuitry configured:

to receive a hybrid broadcast signal;

to demodulate the hybrid broadcast signal to produce an analog audio stream and a digital audio stream;

to use a normalized cross-correlation of envelopes of the analog audio stream and the digital audio stream to measure a time offset between the analog audio stream and the digital audio stream;

to compute a coarse envelope cross-correlation over a first range of lag values to locate a vicinity of the time offset; and

to subsequently compute a fine envelope cross-correlation over a second range of lag values, wherein the second range of lag values is narrower than the first range of lag values.

13. The radio receiver of claim 12 , wherein the processing circuitry is further configured to use quadratic interpolation of peak indices to improve resolution of a computed peak lag.

14. The radio receiver of claim 12 , wherein the processing circuitry is further configured:

to compute the normalized cross-correlation of envelopes using a vector of samples of the analog audio stream and a vector of samples of the digital audio stream to produce bifurcated and composite correlation peaks; and

to compare the bifurcated and composite correlation peaks for correlation validation via temporal consistency.

15. The radio receiver of claim 12 , wherein the processing circuitry is further configured:

to compute the normalized cross-correlation of envelopes using a vector of samples of the analog audio stream and a vector of samples of the digital audio stream to produce current and previous peaks; and

to compare the current and previous peaks for correlation validation via temporal consistency.

16. The radio receiver of claim 12 , wherein the processing circuitry is further configured to calculate phase-adjusted frequency-domain correlation coefficients to validate the time offset.