| 摘要 |
A circuitry has a calibration signal generator, a higher frequency range output level adjusting circuit and a recording bias current adjusting variable resistor. The signal generator continually alternately gives output two kinds of calibration signals of lower and higher frequencies. The higher range adjusting circuit is operatively connected with the variable resistor, and adjusts output sound level, as indicated at an indicator, only of the higher frequency signal of the two calibration signals.
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