Audio Merger

How to use the audio merger

1. Choose the audio files; add more at any time.
2. Reorder them, and set a gap or a crossfade.
3. Merge and download the WAV.

About this tool

Files are decoded, joined in the order you arrange them, and written out as one. Clips can be reordered, a gap of silence can be inserted between them, or they can be crossfaded so one fades out as the next fades in.

Matching is done upwards rather than downwards: the highest sample rate and channel count in the set are used, so adding a mono voice recording to a stereo music track does not flatten the music to mono. The reverse — matching the worst file — is the easier implementation and quietly damages the good material.

Joins get a ten-millisecond fade by default, which sounds like a detail and is not. A hard cut between two clips leaves a discontinuity in the waveform, and a discontinuity is heard as a click; it is the single most common fault in joined audio, and a fade shorter than anyone can perceive removes it entirely.

The crossfade uses an equal-power curve rather than a linear one. Two uncorrelated signals faded linearly dip in loudness through the middle of the overlap, because their combined power falls even as the sum of their amplitudes stays constant — the sine and cosine pairing keeps the power steady, which is why it sounds even.

The output is WAV, and that is a real limitation. Browsers decode MP3, M4A, OGG and FLAC and encode none of them, so the alternative would be bundling a codec several times the size of this whole site.

Common uses

• Joining recorded segments into one interview or episode.
• Combining voice notes into a single file.
• Assembling clips with a crossfade between them.

Frequently asked questions

What formats can I merge?

Anything the browser decodes — MP3, M4A, WAV, OGG and FLAC — and they can be mixed freely. The output is WAV.

Why is the result a WAV, and so large?

Because browsers can decode compressed audio but not encode it. Compress the result afterwards with whatever your system provides.

Why is there a fade at each join?

A hard cut leaves a discontinuity in the waveform, which is heard as a click. A ten-millisecond fade removes it and is far too short to perceive as a fade.