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Noise Suppression Method With Compressor/Expander Coupling for the Magnetic Recording and Playback of Analog Signals

IP.com Disclosure Number: IPCOM000034445D
Original Publication Date: 1989-Feb-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 2 page(s) / 41K

Publishing Venue

IBM

Related People

Maier, H: AUTHOR

Abstract

An essential requirement for obtaining the original signal when a noise-suppressed magnetically recorded analog signal is played back is that the dynamic expansion during playback must be exactly synchronous with the dynamic compression during recording. As most known noise suppression systems are unsuited to meeting this requirement, an approximation is obtainable only by certain trade-offs. The problem of existing methods is that the playback expander does not directly and without delay control the recording compressor but that the control voltage has to be derived from the playback signal. However, the proposed method provides for the compressor/expander to be directly connected for control purposes. The figure is a block diagram of the recording system used.

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Noise Suppression Method With Compressor/Expander Coupling for the Magnetic Recording and Playback of Analog Signals

An essential requirement for obtaining the original signal when a noise- suppressed magnetically recorded analog signal is played back is that the dynamic expansion during playback must be exactly synchronous with the dynamic compression during recording. As most known noise suppression systems are unsuited to meeting this requirement, an approximation is obtainable only by certain trade-offs. The problem of existing methods is that the playback expander does not directly and without delay control the recording compressor but that the control voltage has to be derived from the playback signal. However, the proposed method provides for the compressor/expander to be directly connected for control purposes. The figure is a block diagram of the recording system used. Above the frequency band to be transmitted, a frequency- modulated signal is recorded, whose frequency indicates the respective effective level increase of the compressor, which in the audio range is between 21 and 22 kHz. In this range, the frequency response decreases in most cases, but this has no adverse effect, since the frequency is modulated. In addition, frequency modulation prevents the relevant signal from being influenced by compression or expansion processes. Thus, the following association would be conceivable, for example: 21 kHz = no level increase ......22 kHz = 30 dB level...