Audio processing system for restoring bass frequencies

Details Audio processing system for restoring bass frequencies Audio processing system for restoring bass frequencies

1985-07-11

1987-10-06

Isen, Forester W.

Electrical audio signal processing systems and devices

Binaural and stereophonic

381 98, 84 119, 84DIG9, H04R 500, G10H 102

Patent

active

046988424

ABSTRACT:
An audio processing system for injecting left and right channel audio signals with a signal having a fundamental frequency component that is half the frequency of the highest amplitude low frequency component in the left and right channel audio signals. The left and right channel audio signals are combined to form a monaural signal that is low pass filtered and applied to a demodulator circuit. The demodulator circuit generates a control signal having a frequency that is half the frequency of the highest amplitude frequency component in the signal at the output of the band pass filter. The control signal varies the phase of the signal at the output of the band pass filter according to the polarity of the control signal. The resulting signal is selectively added to the left and right input signals. In order to prevent the audio processing circuit from producing annoying artifact when the audio signals are vocally generated, a voice detector determines that the input signals are from a vocal source and then disables the audio processing circuit. The voice detector operates by comparing the monaural (left plus right) signal to a differential signal (left minus right). Vocal source material has a relatively higher monaural signal while a musical source has a relatively higher differential signal.

REFERENCES:
patent: 3213180 (1965-10-01), Cookerly et al.
patent: 3535969 (1970-10-01), Bonger
patent: 3651242 (1972-03-01), Evans
patent: 4182930 (1980-01-01), Blackmer
patent: 4441203 (1984-04-01), Fleming
patent: 4463650 (1984-08-01), Rupert
patent: 4542525 (1985-09-01), Hopf

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