Complex sentence: In sound recording, sonic leakage (also called "spillage" or "bleeding") occurs when audio intended for one track is picked up inadvertently by another track's microphone in a multitrack recording.
Split into simpler sentences: In sound recording, sonic leakage (also called "spillage" or "bleeding") occurs, when several microphones are used. Then audio intended for one track is picked up inadvertently by another track's microphone in a multitrack recording.