Sennheiser eW 300 IEM G2 Notice D'emploi page 84

Squelch
Pilot tone squelch
The transmitter adds a 19-kHz pilot tone to the audio signal. The receiver
checks incoming audio signals to see if the pilot tone is present. In the
absence of the 19-kHz signal, the receiver's audio output will remain muted,
even if a strong RF signal is present.
This prevents strong interfering signals from causing hissing noise in the
receiver when the transmitter is switched off.
Field strength-dependent squelch
Depending on the strength of the received RF signal, the receiver's audio
output is opened or muted. Via the "SQELCH" menu of the receiver, the
squelch threshold can be adjusted in three steps (LO, MID, HI).
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