Dynamic magnetic information storage or retrieval – Modulating or demodulating
Patent
1991-01-23
1993-07-27
Pascal, Robert J.
Dynamic magnetic information storage or retrieval
Modulating or demodulating
360 18, 360 28, G11B 502
Patent
active
052315428
ABSTRACT:
The present invention relates to a method and device for recording the low frequency band of an audio signal on an amplitude modulated carrier above the highest frequency component of the audio signal. The carrier frequency is at least 19 kHz and is recorded at an adequate level above the noise floor typically about 10 to 30 dB below peak level. The audio signal with the low frequency band optionally attenuated or omitted is directly recorded in the normal audio region on the same track with the corresponding AM carrier. During playback the amplitude modulated carrier is recovered using a highpass or bandpass filter, demodulated and the low frequency signals mixed with the audio. When applied to audio tape reproduction, the present invention improves bass response as compared to direct recording alone. High quality low noise tape and narrow bandwidth of the AM signal allows audio reproduction with high signal to noise ratio. The invention is a further improvement over techniques using an FM carrier recorded in the ultrasound region. Unlike FM, the AM carrier is affected equally by wow and flutter as compared to the directly recorded audio, i.e. the frequency components are shifted in pitch by the same amounts allowing the low frequency components recorded on the AM carrier to stay "in tune" with the rest of the audio when subjected to the effects of wow and flutter. Less stringent requirements on wow and flutter in the tape transport mechanism and low cost of the AM system allow its use in home, portable and automobile tape equipment. To further improve the signal to noise ratio, the frequency components of the signal recorded onto the AM carrier can be companded.
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Neyzari Ali
Pascal Robert J.
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