First: watch the meters in OBS
Talk and watch the meters in OBS’s Audio Mixer. If they don’t move, YouTube has nothing to send: the fault is your microphone or the device OBS listens to. If they move but viewers hear nothing, the sound is lost between OBS and YouTube: the track the stream sends, the audio encoder or YouTube’s ingest. Live Control Room says which, in its stream health messages.
1. The meters don’t move
Open Settings, Audio and check that Desktop Audio and Mic/Auxiliary Audio name your devices, not Disabled. Unmute each source in the Audio Mixer. If the microphone works in other apps but not in OBS, follow microphone not showing up in OBS; the microphone test shows whether your system hears it at all.
2. The meters move, but the stream is silent
In Settings, Output with the Output Mode on Advanced, the Streaming tab has an Audio Track: the one track your stream sends. Then open Advanced Audio Properties from the Audio Mixer and check that each source has that track ticked under Tracks. OBS’s own guide leaves every source on Track 1, the stream’s default; a source taken off it plays in OBS but not on YouTube.
Simple output mode has no track choice: if you moved to Advanced to record separate tracks, this is the first place to look.
3. Read YouTube’s message
Open Live Control Room and look at the stream health messages. “Please provide one audio stream. The ingestion stream contains no audio stream” means YouTube receives no sound at all: OBS is sending an empty track, so go back to step 2. YouTube also asks for only one audio stream and says several cause ingestion problems.
YouTube takes AAC or MP3 audio, recommends 128 kbps, and asks for 44.1 kHz when it flags the sample rate. If its message names either, set the audio bitrate in Settings, Output and the Sample Rate in Settings, Audio, then restart the stream.
4. Check what OBS actually sends
YouTube’s own troubleshooting asks you to check how the stream sounds in the encoder itself. A test recording helps only if it carries the stream’s track: in Advanced output mode the Recording tab picks its own tracks, so a recording can have your voice while the stream doesn’t. Match the two, record a minute and play it back; if it is silent, the fault is in OBS’s sources, not YouTube.
Questions
Viewers hear the game but not me. The microphone is the source off the stream’s track, or muted in the Audio Mixer: step 2 again, for that one source.
I hear my stream’s sound in my headphones, so it must be working. Not necessarily: what you monitor in OBS is not what the stream sends. Check the stream itself, in Live Control Room’s preview or a recording.