Method and apparatus for improving the quality of AM compatible digital broadcast system signals in the presence of distortion

A system for reducing perceived distortion in an output audio signal derived from an amplitude modulated compatible digital broadcast signal having a monophonic portion and a stereo portion, said system comprising:

• (a) means for demodulation said monophonic portion of said signal to produce a demodulated monophonic signal;
• (b) means for demodulation said stereo portion of said signal to produce a demodulated stereo signal having a signal-to-noise ratio;
• (c) means for estimation the signal-noise ratio in the demodulated stereo signal, said means for estimating the signal-noise ratio in the demodulated stereo signal comprising means for estimating the noise in the demodulated stereo signal, means for estimating the power of the demodulated stereo signal, and means for dividing the estimated noise in the demodulated stereo signal into the estimated power of the demodulated stereo signal, wherein said means for estimating the noise in the demodulated stereo signal comprises means for subtracting the demodulated stereo signal from said stereo portion of said amplitude modulated compatible digital broadcasting signal to obtain an error estimate, means for squaring said error estimate, and means for averaging said squared error estimate;
• (d) means for comparing the estimated signal-to-noise ratio in the demodulated stereo signal to a threshold level set at the minimum acceptable signal quality;
• and
• (e) means responsive to said means for comparing for synthesizing discrete left and right stereo outputs.