Audio Joiner

Yes. MP3, WAV, FLAC, M4A, AAC, OGG and sound from videos can all be mixed. They're first converted to one sample rate (the higher one among the files, up to 48 kHz); if any clip is stereo the result is stereo, and mono clips play the same sound in both channels.

If one recording was cut into parts, pick back to back. To run several songs into one non-stop track, pick crossfade (one fades out as the next fades in, overlapping 0.5 to 10 seconds). For separate songs or lessons, pick a gap to leave a few seconds between them.

2 to 20 files at a time, each up to 20 minutes and 500 MB. The joined result can be up to 60 minutes on a computer and up to 20 minutes on a phone (phones have less memory, and very long audio can crash the page).

It brings each clip's average loudness to the middle level of the set — a rough adjustment, not professional loudness normalization. Each clip is raised by 12 dB at most, and raising never pushes peaks past full scale. Also, whenever any spot in the joined result would go past full scale — where two clips overlap in a crossfade, or because a source file was recorded very hot (loud MP3 and AAC files often go slightly over after decoding), even when joined back to back — the whole file is turned down slightly to prevent clipping. The balance between clips is unchanged, and the result page says by how many dB.

Nothing is uploaded — joining happens entirely in your browser. Log in to use it free with no usage limits. It works in phone browsers too; use fewer clips at a time. In WeChat you can join and preview, but to save the file, tap “···” in the top-right corner and open it in a browser first.