Audio Joiner

How the Audio Joiner works

How the audio joiner works

Joining audio sounds trivial until you try to do it by hand. Files come in different formats, at different sample rates, with different channel counts, and simply appending the bytes of one MP3 to another produces something that half the players in the world will refuse to open. This page does it properly: each file is decoded to raw samples with the browser's own decoder, laid end to end on a timeline, and rendered back out as a single clean file.

Order and gaps. Files are listed in the order they were dropped, and each drop adds to the list rather than replacing it, so you can bring files in one at a time from different folders. Move a file with Up and Down, or take it out with Remove. The gap setting inserts that many milliseconds of pure silence after every file except the last, which is useful for separating chapters of an audiobook or tracks on a demo; leave it at zero for a seamless join.

Mismatched files. The output takes its sample rate from the first file in the list and its channel count from the widest file. A 48 kHz file joined after a 44.1 kHz file is resampled to 44.1 kHz on the way through, and a mono file placed next to stereo files is placed in the centre of both channels. Nothing is level-matched: if one file is much quieter than the others, run it through the Audio Normalizer first, or normalise the finished join.

Formats. Anything your browser can decode can go in — MP3, WAV, M4A, FLAC, OGG and most others — and WAV or MP3 comes out. WAV is the right choice if the result is going into an editor or another tool; MP3 at 192 kbps or above is fine for sharing. Bear in mind that decoding MP3 sources and re-encoding them as MP3 adds one more generation of loss, so if the originals are already MP3 and quality matters, export as WAV and convert once at the end.

Memory. Every file is held in memory as uncompressed samples, roughly ten megabytes per minute of stereo. Joining a handful of songs is nothing; joining a dozen hour-long recordings will strain a laptop, and the page warns you when a file is over an hour.

To join video clips rather than audio, use the video merger.

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