| 摘要 |
A signal processing circuit for improving the signal-to-noise ratio of input signals, such as audio signals recorded on tape, has a low-pass filter circuit for controllably filtering signals at the lower end of the frequency spectrum, and a high-pass filter circuit for controllably filtering signals at the higher end of the frequency spectrum, with the high-pass filter circuit and the low-pass filter circuit defining the only paths through the signal processing circuit for the input signals. Associated control circuitry provides first and second control signals to control the attenuation of signals at the lower-frequency and higher-frequency parts of the spectrum, respectively, in dependence on the amplitude of the input signals in the respective parts of the spectrum. Preferably, the controllable low-pass and high-pass filter circuits are connected in parallel between input and output terminals, a low-frequency band control unit is provided to control the amount of attenuation of the low-pass filter circuit and a high-frequency band control unit is provided to control the cut-off frequency of the high-pass filter circuit. In one practical arrangement for recording audio signals, signals taken from the output terminal of the signal processing circuit are recorded on tape. For playing back these recorded signals, the input and output terminals of the processing circuit are respectively connected to the output terminal and negative feedback input of an operational amplifier.
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