Audio is the part people tend to guess at. Answer three quick questions and get the exact settings to use, plus where to find them in OBS. Runs entirely in your browser — nothing is sent anywhere.
Viewers forgive a slightly soft picture far more easily than bad audio — a mic that's too quiet, clipping, or drowned out by game sound is one of the fastest ways to lose someone in the first ten seconds of a stream. Unlike video, where a single bitrate number covers most of what matters, audio quality comes down to several smaller decisions stacking on top of each other: bitrate, how many separate tracks you're recording, and which filters are actually doing something versus just eating CPU for no benefit.
Multiple tracks matter more than most new streamers realize. OBS can record your mic, game audio, and music as separate tracks even while your live stream mixes them into one — this means you can mute an annoying game sound effect or duck background music in post-production without having to re-record anything, as long as you set the tracks up before you start rather than after. It costs nothing in real-time performance to record extra tracks; it only costs you flexibility later if you don't.
On filters: a noise gate (cutting audio below a volume threshold) and noise suppression (removing steady background hiss or fan noise) solve two different problems and most setups benefit from having both, in that order, before a compressor which evens out volume swings between quiet and loud speech. Skipping the noise gate is the single most common reason a stream picks up keyboard clatter or room echo that the streamer themselves has stopped noticing.