Audio joiner: merge MP3 and other audio files into one

How to merge audio files

1. Add your files. Click Add files or drop two or more MP3, M4A, WAV, OGG, FLAC or video files onto the joiner. They are decoded on your device and appear as a list, in the order you added them.
2. Put them in order. Drag a clip by its ⋮⋮ grip, or use the ↑ and ↓ buttons, until the list reads top to bottom the way the finished file should play.
3. Trim and balance each clip. Drag across a clip’s waveform (or type Start and End) to keep only the part you want, and use Gain to make a quiet clip louder or a loud one softer. Press ▶ to hear a single clip.
4. Choose the joins. Under Between clips pick an equal-power crossfade, a silence gap or a straight cut, and set its length. The timeline shows exactly where every clip lands.
5. Download. Leave Normalize ticked, pick MP3, WAV or M4A, name the file and press Download. Play first if you want to hear the whole join.

What the joiner does with your clips

Every clip is processed in the same order: it is trimmed to its Start and End, given its own gain, converted to the output sample rate and channel count, and then placed on the timeline after the previous clip. Where two clips meet they either overlap by the crossfade length, are separated by the gap, or simply butt together. Finally the whole result can be normalized and faded at the very start and end, then encoded once.

The joined length is easy to predict: add up the trimmed clip lengths, subtract one crossfade per join, or add one gap per join. Three 1-minute clips with 2-second crossfades come out at 2:56; the same clips with 1-second gaps come out at 3:02. The line under the clip list shows that sum for your clips as you edit.

Crossfade, gap or straight cut?

Crossfades are equal-power: the outgoing clip follows a cosine curve and the incoming one a sine curve, so the combined loudness stays level through the overlap instead of dipping in the middle, which is what a simple linear crossfade does with two different songs. A crossfade can never be longer than half of the shorter of the two clips; if you set 5 seconds next to a 6-second jingle, that join is shortened to 3 seconds and the note under the list tells you. Read crossfades explained for the maths and for choosing a length.

Different formats in, one format out

You can mix files freely — an MP3 recorded on a phone, a 48 kHz WAV from a camera and a mono voice memo. The output uses the highest sample rate of your clips (or the rate you pick under Sample rate) and is stereo if any clip is stereo; mono clips are placed in the centre and stereo clips are mixed down if you tick Mix to mono. Conversion uses the browser’s own high-quality resampler, so pitch and speed never change.

Levels: per-clip gain and Normalize

Clips from different sources are rarely the same loudness. Use each clip’s Gain (−12 to +12 dB) to balance them by ear — music beds under or between speech usually sound right about 6 dB lower than the voice. Normalize then scales the finished join so its highest peak sits at −1 dBFS: as loud as possible without clipping, with every clip’s relative level kept. If you turn Normalize off and boost several clips, the player warns you when the joined file would clip.

Quality and file size

Decoded audio is joined as 32-bit floating point and encoded once, so merging MP3s costs a single generation of encoding — inaudible at 192 kbps or more. Choose WAV for a lossless master you will edit further, MP3 for sharing and podcasts, or M4A for Apple devices (where your browser has an AAC encoder). The estimate under the Download button updates with the length and format. MP3 and AAC add a few milliseconds of encoder padding at the start and end of the file, but not between the clips, because the joins are made before encoding.

Need to cut a single file instead? Use the MP3 cutter, or cut an MP3 into parts to go the other way. The guide to merging audio files walks through a complete example.

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