Sound multiplex receiver

In a sound multiplex receiver having a sound multiplex discriminating circuit for identifying between a monaural and at least one type of multiplex broadcast from signals superposed on said broadcast and for producing at least one mode signal for controlling channel separating of said broadcasts, a mode signal processor comprising:

• processing means for processing a mode signal of a broadcast and controlling separating of channels of said broadcast;
• signal strength detecting means for detecting a ratio of signal to noise in said broadcast;
• and
• control means for controlling said processing means in response to an output of said signal strength detecting means;
• wherein said detecting means detects a field strength of said broadcast;
• wherein said processing means comprises integrator means for integrating said detection signal;
• wherein said integrator means comprises a controllable resistance-capacitance time constant circuit which determines the integration period of said integrator;
• and
• wherein said control means controls the time constant circuit to provide an integration period which is longer for a detection signal corresponding to a field strength decrease from a multiplex broadcast signal to a monaural broadcast signal than for a field strength increase from a monaural broadcast field strength to a multiplex broadcast field strength.