Before revision: To minimize the effects of voice audio on squelch operation, the audio from the receiver's detector is passed through a high-pass filter, typically passing 4,000 Hz ( 4 kHz ) and above, leaving only high frequency noise.
After revision: To minimize the effects of voice audio on squelch operation, the audio from the receiver's detector is passed through a high-pass filter, typically passing 4,000 Hz ( 4kHz ) and above, leaving only high frequency noise.