Signal compression and expansion circuits for analogue recorder - uses operational amplifier with diodes forming precision rectifier to ensure four quadrant multiplier produces correct output signal phasing

摘要

An input signal for compression is applied to a non inverting amplifier (6) whose gain is adjusted to ensure that the output level is the same as the input. The output is applied to a four quadrant multiplier (7) which obtains the square root of its input signal (Z2). The compressed output cycles of waveform are obtained from the X outputs (1,2) and are recombined in an operational amplifier (8). An operational amplifier with diodes at its output ensure that the correct output signal phase is used. For signal expansion a similar circuit is used where the input is applied to the Y input of a four quadrant multiplier. Diodes used in conjunction with an operational amplifier connected to the X inputs (1,2) ensure that the correct signal phase is obtained at the output (z1,5). The system increases the dynamic range of sounds during a recording, and provides noise suppression.