Cut a piece of audio in the middle and the waveform at the edit point almost never lands exactly on zero. On playback, the speaker cone is forced to jump instantaneously from one position to another — in signal-processing terms, a discontinuity equivalent to a step, whose energy spreads across the entire spectrum (the same spectral-leakage phenomenon familiar from spectrum analysis; see the discussion of discontinuities in Stanford CCRMA’s online textbook Spectral Audio Signal Processing). What your ear hears is a short, sharp click or pop.
The same physics explains why butt-joining two clips so often produces noise at the seam: the two waveforms are vanishingly unlikely to match in both amplitude and slope at the junction.
A zero crossing is where the waveform passes through zero amplitude. Cutting there minimizes the jump, so the click largely disappears. Many editors offer “snap to zero crossing”; editing manually, zoom in to sample level and cut where the wave crosses the center line for the same effect.
Zero crossings guarantee amplitude continuity but not slope continuity, so bass-heavy material (bass guitar, kick drums) can still leave a faint thump — which is where the second fix comes in.
Apply an extremely short fade-out and fade-in (a few to a few dozen milliseconds) at the edit point, ramping the amplitude smoothly to zero and back — eliminating the discontinuity at its root. This is also how a crossfade works: the outgoing fade overlaps the incoming one, leaving a perfectly seamless join.
In the MP3 Cutter, you can apply fade-in/fade-out to the selected region directly, so exports come with smooth edit points built in.
Try the MP3 Cutter Now