Mastering

Mixing balances the parts against each other. Mastering treats the finished result as a whole and brings it to a consistent, comfortable level, with any last broad tonal correction, gentle compression and a limiter to stop peaks. For a talking-head channel this is a light touch. Match the level across every video you publish so viewers never reach for the volume. Leave headroom instead of squashing everything flat, because chasing maximum loudness costs you dynamics and makes speech tiring across twenty minutes. If you only do one thing here, keep the level identical from upload to upload.