Audio Joiner

What this tool does

Audio Joiner combines MP3, WAV, M4A, OGG and FLAC files into a single WAV. Reorder clips by dragging, insert a gap of silence or an equal-power crossfade between them, match levels with per-file peak normalisation, and resample everything to one sample rate automatically.

Recordings often come in pieces: a lecture split across several voice memos, podcast segments recorded separately, songs you want as one continuous mix. Simply appending the files byte by byte only works for some formats and breaks as soon as the sample rates or channel counts differ.

This joiner decodes each file with the Web Audio API, converts every part to a common sample rate and channel layout with the browser’s own resampler (OfflineAudioContext), and then writes the samples one after another into a single WAV. Between clips you can leave a gap of silence or overlap them with an equal-power crossfade, which uses sine and cosine curves so the combined loudness stays even through the transition. All processing happens on your device.

How to use Audio Joiner

1. Drop two or more audio files onto the upload area; you can add more at any time.
2. Put them in order by dragging the rows or using the up and down arrows, and press Play on any row to check it.
3. Under Transition choose Gap and set the silence between files, or Crossfade and set its length.
4. Choose the output Sample rate and Channels, or leave them on automatic.
5. Turn on Match levels if the files were recorded at different volumes.
6. Click Join audio, listen to the result and download the WAV.

Tips for better results

• A 1 to 3 second crossfade suits music mixes; for speech, a 0.3 to 0.5 second gap usually sounds more natural than a crossfade.
• Automatic sample rate picks the highest rate among your files, so no part is downsampled unnecessarily.
• Mixing mono and stereo clips? Automatic channels produces stereo and places mono parts in the centre.
• Match levels normalises each file’s peak to -1 dBFS; for spoken word you can refine the overall loudness afterwards with the Audio Volume Changer.

Common use cases

• Combining several voice memos of one meeting or lecture into a single file.
• Building a continuous workout or party mix with crossfades between songs.
• Assembling podcast intro, interview and outro segments into one episode.
• Joining audiobook chapters that were delivered as separate tracks.

Common mistakes to avoid

• Adding the files in the wrong order: the list is joined top to bottom, so check the numbers before joining.
• Using a crossfade longer than a short clip; the overlap is limited to the length of the shorter of the two neighbouring files.
• Joining many long files on a phone with little memory; each minute of stereo audio uses about 21 MB while decoded.