Merge audio files
To merge audio files is to join several recordings into one: back to back, with a pause or with a soft crossfade. Choose the files, set the order and save as MP3 or WAV, all in your browser with nothing uploaded. If you like, the tool evens out the loudness of the parts.
Source: ITU-R BS.1770 – Algorithms to measure audio programme loudness and true-peak audio level. Updated: .
How it is calculated
In short: the tool reads each file in the browser, brings all of them to the same sample rate (44.1 kHz, stereo) and lays them one after another in your order. Between the parts there can be a pause or a crossfade, where the end of one recording fades out while the next one comes in.
How it works
- Drop two to twenty files or choose them. The sound of videos works too.
- Adjust the order with the arrows.
- Pick the transition: back to back, with a pause (0.5 to 10 seconds) or crossfade.
- Optionally even out the loudness, choose a format (MP3 or WAV) and click “Merge and save audio”. You can listen to the result right away.
The transitions
- Back to back: the files follow each other without any silence in between.
- With a pause: silence of the chosen length between the parts, handy for audiobook chapters or voice messages.
- Crossfade: the end of one file fades out while the next fades in (equal-power crossfade, so the loudness stays even). With very short files the crossfade is at most half their length.
Even out loudness
The option measures the loudness of each file according to ITU-R BS.1770 (LUFS) and brings all of them to the average. A limiter prevents clipping. Silent files stay unchanged.
Honest limits
- When merging, all files are decoded and saved anew. With MP3 this means new compression; WAV avoids that but is larger.
- At most 20 files and 20 minutes together are possible. Mono is doubled to two channels, more than two channels are cut to stereo.
- Tags and cover art of the source files are not carried over.
Privacy
The files are processed only in your browser and are not uploaded.
Frequently asked questions
How can I merge audio files?
Choose the files, set the order with the arrows, pick the transition and click “Merge and save audio”. You get an MP3 or WAV file.
Can I mix MP3 and WAV?
Yes. All files are decoded and brought to 44.1 kHz stereo before they are joined. M4A, OGG, FLAC and the sound of videos work too.
How do I crossfade two tracks?
Choose “Crossfade” and set the length. The end of the first file fades out while the second comes in. The total length shrinks by the crossfade.
What is “Even out loudness” for?
If the files differ in loudness, the result jumps. The option brings all of them to the same loudness (LUFS), with a limiter against clipping.
Are my files uploaded?
No. Merging runs entirely in your browser; the files never leave your device.
Is there a limit on length?
Up to 20 files and 20 minutes in total. For longer recordings split the work into two steps.
Sources and legal basis
- ITU-R BS.1770 – Algorithms to measure audio programme loudness and true-peak audio level
- EBU R 128 – Loudness normalisation and permitted maximum level
- Wikipedia – Fade (audio engineering): Crossfade, equal-power
- MDN – BaseAudioContext.decodeAudioData()
- MDN – Web audio codec guide
- LAME MP3 Encoder (LGPL)
- lamejs – JavaScript port of LAME (LGPL-3.0), fork @breezystack/lamejs
- Microsoft/IBM – Multimedia Programming Interface and Data Specifications 1.0 (RIFF WAVE)
- Open-source licenses of the libraries used (MIT, LGPL-3.0)
As of: · Editorial policy
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