For that frequency response in record and playback, audio magnetic tape recorders are provided with high-frequency bias-current and frequency-characteristic adjustments. These adjustments are necessary because of the variety of magnetic-tape characteristics from different tape manufacturers. Domestic tape recorders are equipped with a preset tape selector to set optimum bias current and recording-current equalization. It is desirable to adjust bias and recording equalization for each individual tape, but the procedure is hard for consumers, as it requires an audio-frequency oscillator, voltmeter, and other instruments. Proper setting of optimum bias is a serious problem for high-fidelity recording. To solve these problems, an automatic bias-current adjusting circuit and an automatic recording-equalization adjusting circuit have been developed. Time required to complete the adjustments is about 20 seconds. Optimum values of bias current and recording equalization are memorized by the `analog memory,` a newly developed device. Examples of applications to professional-quality tape recorders are also given.
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