i was building a meeting recorder however when i record the mic, it will record the sound coming from the speaker too

so in the end there are 3 noises recorded

1) sound from speaker
2) sound from mic
3) sound coming out from speaker and then enter mic

when merge all 3 of them , will have echo


how do sound recorder software prevent the recording of 3) ?

https://www.techsmith.com/blog/not-late-red...ecordings-free/

It'll be easier to ensure your mic doesn't pick up sounds other than from the direction of the sounds you're trying to record. e.g. use a directional microphone, so your (3) would be minimized.

There are other tricks which include ensuring your mixer input is correctly picking only (1) and (2).

Consider using https://krisp.ai/blog/obs-remove-background-noise/ or nvidia RTX Voice if you have access to them to add additional noise filter on your mic input.