Suppression of pulse type noise signals from disc recording - using detector for abrupt reduction of amplifier gain for duration of disturbance

摘要

The suppression circuit is principally for disturbing signals emanating from disc recordings, partic. pulse type. When operating at low signal levels, with dynamic expansion circuits active, a pulse distortion is also amplified, and the decay time to reach the original signal level can be relatively long. To overcome this undesirable feature a pulse distortion detector is used. This acts on rate of change and relative amplitude of the signal coming from the disc. When such a signal is detected the expander amplifier gain is instantaneously reduced to a low value, and held low until the disturbance is over. The effect of the disturbance is thereby practically unnoticeable in the resulting output. The circuit can operate by solid state switching of a different amplifier reference voltage for the duration of the disturbance.