| 摘要 |
In a signal expander, the envelope of an input signal (S1) to be expanded is detected (30) and applied as a control signal (S3) to the gain control input (18) of a variable gain device (14) which expands the input signal. The control signal is applied to the variable gain device via an adaptive filter (40) having improved ripple reduction and transient performance characteristics to minimize audibility of gain changes. The adaptive filter includes a low pass filter (50,52) for producing a smoothed control signal essentially free of ripple and an analog gate (70,74,78) for coupling the greater of the smoothed signal or a further signal to the variable gain device, the further signal being equal to the detector output signal less a constant. Compression of an input signal is provided by applying the input signal to the non-inverting input (110) fig 3 not shown of an amplifier (100) and feeding the (compressed) output signal (S1) of the amplifier to the expander (30,40, 14) and feeding the output signal (S2) of the expander to the inverting input of the amplifier (100). <IMAGE> |
