Spill / Bleed
Definition
Unwanted sound from one source captured by a microphone intended for a different source. Common in live recording situations where multiple instruments are recorded simultaneously in the same room — drum overheads pick up guitar amplifiers, vocal mics pick up headphone leakage.
In Simple Terms
When a microphone picks up sounds it wasn't meant to capture — the drums leaking into the vocal mic, the guitar amp bleeding into the piano mic. Some bleed is inevitable in live recording. It can add character, but too much makes individual tracks impossible to mix independently.
In Practice
During a live band tracking session, the drum overhead microphones capture significant bleed from the guitar amplifier positioned nearby. The engineer repositions the amp and adds a gobo (acoustic barrier) to reduce the spill to an acceptable level.
Common Confusion
Spill is not always a problem. In many classic recordings, controlled bleed between instruments contributes to the cohesive, live sound. The issue arises only when the bleed prevents independent processing of individual tracks.