Method and apparatus for level control in blending an audio signal in an in-band on-channel radio system

Abstract

A method for processing a digital audio broadcast signal includes: separating an analog audio portion and a digital audio portion of the digital audio broadcast signal; determining the loudness of the analog audio portion and the digital audio portion over a first short time interval; using the loudness of the analog and digital audio portions to calculate a short term average gain; determining a long term average gain; converting one of the long term average gain or the short term average gain to dB; if an output has been blended to digital, adjusting a digital gain parameter by a preselected increment to produce a digital gain parameter; if an output has not been blended to digital, setting the digital gain parameter to the short term average gain; providing the digital gain parameter to an audio processor; and repeating the above steps using a second short time interval.

What is claimed is: 
     
       1. A method for processing a digital an audio broadcast signal including multiple audio streams using an audio signal receiver, the method comprising:
 (a) separating an analog audio portion a first audio sample stream of the digital audio broadcast signal from a digital audio portion second audio sample stream of the digital audio broadcast signal using the audio signal receiver; 
 (b) determining a loudness of the analog audio portion first audio sample stream over a first short time interval; 
 (c) determining a loudness of the digital audio portion second audio sample stream over the first short time interval; 
 (d) using the loudness of the analog audio portion first audio sample stream and the loudness of the digital audio portion second audio sample stream to calculate a short term average gain; 
 (e) determining a long term average gain; 
 (f) converting one of the long term average gain or the short term average gain to dB decibels (dB) and providing the converted average gain to an audio processor; 
 (g) if an output of a receiver has been blended to digital, performing one of blending an output of a receiver to the second audio sample stream and adjusting a digital second audio sample stream gain parameter toward the long term average gain by a preselected increment, to produce an adjusted digital gain parameter; (h) if the output of the receiver has not been blended to digital or not blending the output of the receiver to the second audio sample stream and setting the digital second audio sample stream gain parameter to the short term average gain; 
 (i)(h) providing the digitalsecond audio sample stream gain parameter adjusted byfrom step (g) or step (h) to the audio processor; and 
 (j)(i) repeating steps (a) through (i)(h) using a second short time interval. 
 
     
     
       2. The method of  claim 1 , wherein:
 the short term average gain is a linear ratio of analog audio power of the first audio sample stream and digital audio power of the second audio sample stream. 
 
     
     
       3. The method of  claim 1 , wherein:
 the digital second audio sample stream gain parameter is adjusted toward the short term average gain; and 
 the preselected increment is 1 dB. 
 
     
     
       4. The method of  claim 1 , wherein:
 the long term average gain comprises a running average of the short term average gain. 
 
     
     
       5. The method of  claim 1 , wherein:
 the long term average gain is determined independently of the short term average gain. 
 
     
     
       6. The method of  claim 1 , wherein:
 the long term average gain is converted to dB if a long time interval has been met and the short term average gain is converted to dB if the long time interval has not been met. 
 
     
     
       7. The method of  claim 6 , wherein the long time interval comprises an integer multiple of the short time intervals. 
     
     
       8. The method of  claim 6 , wherein:
 the short time interval is in a range from 1 to 5 seconds and the long time interval is in a range from 5 to 30 seconds. 
 
     
     
       9. The method of  claim 1 , wherein:
 the analog audio portion first audio sample stream comprises a stream of samples analog modulated program material; and 
 the digital audio portion second audio sample stream comprises a stream of samples digitally modulated program material. 
 
     
     
       10. The method of  claim 1 , wherein the measurements of the levels of the analog audio portion first audio sample stream and the digital audio portion second audio sample stream are performed in accordance with the International Telecommunications Union Recommendation (ITU-R) BS.1770 specification. 
     
     
       11. A radio An audio signal receiver comprising:
 processing circuitry configured to: 
 (a) separate an analog a first audio portion sample stream of the digital an audio broadcast signal from a digital second audio portion sample stream of the digital audio broadcast signal; 
 (b) determine a loudness of the analog first audio portion sample stream over a first short time interval; 
 (c) determine a loudness of the digital second audio portion sample stream over the first short time interval; 
 (d) use the loudness of the analog first audio portion sample stream and the loudness of the digital second audio portion sample stream to calculate a short term average gain; 
 (e) determine a long term average gain; 
 (f) convert one of the long term average gain or the short term average gain to dB decibels (dB) and provide the converted average gain to an audio processor; 
 (g) if an output of a receiver has been blended to digital, perform one of blend an output of a receiver to the second audio sample stream and adjust a digital second audio sample stream gain parameter by a preselected increment to produce an adjusted digital gain parameter; (h) if the output of the receiver has not been blended to digital, or not blend the output of the receiver to the second audio sample stream and set the digital second audio sample stream gain parameter to the short term average gain; 
 (i)(h) provide the digitalsecond audio sample stream gain parameter adjusted byfrom step (g) or step (h) to the audio processor; and 
 (j)(i) repeat steps (a) through (i)(h) using a second short time interval. 
 
     
     
       12. The radio audio signal receiver of  claim 11 , wherein:
 the short term average gain is a linear ratio of analog audio power and digital audio power. 
 
     
     
       13. The radio audio signal receiver of  claim 11 , wherein:
 the digital second audio sample stream gain parameter is adjusted toward the short term average gain; and 
 the preselected increment is 1 dB. 
 
     
     
       14. The radio audio signal receiver of  claim 11 , wherein:
 the long term average gain comprises a running average of the short term average gain. 
 
     
     
       15. The radio audio signal receiver of  claim 11 , wherein:
 the long term average gain is determined independently of the short term average gain. 
 
     
     
       16. The radio audio signal receiver of  claim 11 , wherein:
 the long term average gain is converted to dB if a long time interval has been met and the short term average gain is converted to dB if the long time interval has not been met. 
 
     
     
       17. The radio audio signal receiver of  claim 16 , wherein the long time interval comprises an integer multiple of the short time intervals. 
     
     
       18. The radio audio signal receiver of  claim 16 , wherein:
 the short time interval is in a range from 1 to 5 seconds and the long time interval is in a range from 5 to 30 seconds. 
 
     
     
       19. The radio audio signal receiver of  claim 11 , wherein:
 the analog first audio portion sample stream comprises a stream of samples analog modulated program material; and 
 the digital second audio portion sample stream comprises a stream of samples digitally modulated program material. 
 
     
     
       20. The radio audio signal receiver of  claim 11 , wherein the measurements of the levels of the analog first audio portion sample stream and the digital second audio portion sample stream are performed in accordance with the International Telecommunications Union Recommendation (ITU-R) BS.1770 specification.