Your callsign is showing.
A compander is a noise-reduction system that compresses your audio on transmit and expands it on receive. The name is a portmanteau of "compressor" and "expander." When both radios in a conversation have compander enabled, the result is noticeably clearer audio with reduced background noise.
On the transmitting side, the compander compresses the audio's dynamic range — it makes quiet sounds louder and loud sounds quieter, squeezing everything into a narrower range. This compressed signal travels over the air. On the receiving side, the compander expands the audio back to its original dynamic range, restoring the natural loud-and-quiet variation. Because the background noise was compressed along with the speech, the expansion process pushes it back down below audible levels, making the voice stand out much more clearly.
Compander is usually a simple on/off toggle in your radio's menu, often labeled "Compander," "COMP," or "Compand." It can typically be set per channel. Enable it on both the transmitting and receiving radio:
This is the most important thing to know about compander: both radios must have the same setting. If one radio has compander on and the other has it off, the audio will sound distorted, muffled, or "pumping" (volume surging up and down unnaturally). This is because one side is compressing or expanding audio that the other side isn't compensating for.
Important: Do not use compander on repeaters. You can't guarantee that every radio accessing the repeater has compander enabled, and the repeater itself won't compress or expand the audio. The result would be distorted audio for anyone whose compander setting doesn't match yours. Reserve compander for simplex (direct radio-to-radio) conversations where you control both ends.
Compander is a simple feature that makes a real difference in audio quality — but only when both ends are configured the same way. When in doubt, leave it off.