Reduces static/hash/noise but keep the voice level the same.
1 khz audio frequency is in the middle of the human voice range, so if you cut that freq to reduce noise, you will also cut the voice level, Typical frequency range for voice communication is approx 300 hz to 3000 hz, the range passed by a wired phone. Frequencies below this use noticeable amount of power without enhancing intelligibility, frequencies above this occupy bandwidth that doesn't enhance intelligibility. Other controls on the flex will be more useful addressing noise. I'm kinda deaf, so I cut the lows and highs to increase the voice frequencies in proportion to the others.