Audio Joiner

A hard join between two audio files usually produces an audible click. The cause is a discontinuity: one track's waveform ends mid-cycle at some non-zero value and the next begins somewhere else entirely, and that instant jump is heard as a transient. A crossfade removes it by overlapping the two and ramping one down as the other comes up, so the waveform stays continuous.

Whether to use one depends on the material. For music, a crossfade of half a second to two seconds sounds deliberate and smooth. For speech — joining interview segments, stitching voice notes — a fade makes the words overlap and muddle, and a short silent gap sounds far more natural. That is why both controls are here.

Files with different sample rates are handled by resampling everything up to the highest rate present, never down, so joining a 22 kHz voice note to a 48 kHz recording does not degrade the better one. The mixing and resampling run through an OfflineAudioContext, which gives sample-accurate fades and the browser's own high-quality resampler rather than hand-written interpolation.

Note that the total is shorter than the sum of the parts whenever a crossfade is set, because each overlap removes its own length from the timeline. Set crossfade to zero and the durations add up exactly.

Related: Audio Trimmer, Audio Converter, and Extract Audio from Video.