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

Abstract

A method for processing a digital audio broadcast signal in a radio receiver includes: receiving a digital audio broadcast signal; demodulating the digital audio broadcast signal to produce an analog audio stream and a digital audio stream; determining a digital signal quality value for the digital audio stream; blending an output of the radio receiver from the analog audio stream to the digital audio stream when the digital signal quality value exceeds an adaptive analog-to-digital threshold value; and blending the output of the radio receiver from the digital audio stream to the analog audio stream when the digital signal quality value falls below an adaptive digital-to-analog threshold value, wherein the adaptive digital-to-analog threshold value is lower than the adaptive analog-to-digital threshold value.

Description

FIELD OF THE INVENTION[0001]The described methods and apparatus relate to digital radio receivers and, in particular, to methods and apparatus for blending of analog and digital pathways in digital radio receivers.BACKGROUND OF THE INVENTION[0002]Digital radio broadcasting technology delivers digital audio and data services to mobile, portable, and fixed receivers. One type of digital radio broadcasting, referred to as In-Band On-Channel (IBOC) digital audio broadcasting (DAB), uses terrestrial transmitters in the existing Medium Frequency (MF) and Very High Frequency (VHF) radio bands. HD Radio™ technology, developed by iBiquity Digital Corporation, is one example of an IBOC implementation for digital radio broadcasting and reception.[0003]The National Radio Systems Committee, a standard-setting organization sponsored by the National Association of Broadcasters and the Consumer Electronics Association, adopted an IBOC standard, designated NRSC-5, in September 2005. NRSC-5, the disc...

AI Technical Summary

Problems solved by technology

Similar blending occurs during channel outages which corrupt the digital signal.

However, this has been found to unnecessarily reduce the static digital coverage area by several radial miles, corresponding to a loss of several dB of signal strength.

Although it may seem reasonable to fill-in every digital audio gap, this is generally not desirable because corresponding analog and digital audio segments do not necessarily sound the same.

Intentionally different audio processing on the analog and digital audio streams degrades the listener experience while blending.

In addition, any time or level misalignment between the two streams further degrades the audio quality while blending between them.

Perfect alignment is neither well-defined nor practical due to the different processing between the audio streams, resulting in frequency-dependent group delay and level differences.

Timing misalignment and group delay differences between the two streams can result in a degraded audio signal during the blend ramp.

In addition, field test results and listener feedback suggest that existing blending often occurs too frequently, is sometimes annoying, and can be overly complicated and difficult to configure.

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