Noise suppression
Also called echo cancellation · automatic gain control · AGC
Noise suppression filters background sound out of a microphone signal. Browsers and meeting apps usually apply it together with echo cancellation and automatic gain control, which all change how your voice sounds.
The microphone test turns all three off so you hear what the microphone itself captures. A voice that sounds fine there but muffled in a call points at the app’s processing.
In practice
Voice processing is why your voice can sound fine in one app and strange in another. Noise suppression can clip the start of words. Automatic gain control can pump the volume up during pauses. Echo cancellation can cut you off when someone else talks. All three are useful and all three change your sound.
How to check
Record a clip in the microphone test with all three turned off. Then compare it with how you sound in a call. If the raw clip sounds good, adjust the meeting app’s noise suppression and automatic volume settings rather than the microphone. If the raw clip sounds bad, the problem is the mic or its placement.