Headroom Extension for Slow-Speed Magnetic Recording of Audio
Slow-speed recording (e.g., cassette) has a poor overload level at high frequencies relative to middle frequencies. The recording bias current and equalization are compromises between high frequency saturation and other aspects of performance (distortion, drop-outs, modulation noise, etc.). This paper describes a system, called headroom extension, which continuously adapts the recording bias and equalization to suit the high frequency spectrum of the input signal, as determined by the control circuitry of the Dolby B-Type noise reduction processor. An optimum type of controlled equalization for this purpose is presented. Application of the headroom extension system to cassette recording results in a high frequency signal handling capability improvement on the order of 10 dB above 10 kHz.
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