Audio Merger

What sounds best depends on the material. The total length shown under the options already includes the pauses or overlaps.

Each file is decoded and converted to a common format before joining: the highest sample rate among the files (up to 48 kHz), and stereo if any file is stereo — mono recordings then play in both ears. So a phone voice memo in M4A, a WAV from a recorder and an MP3 can be joined without any preparation. A crossfade is never longer than the shorter of the two files it joins.

MP3 plays everywhere and is the usual choice; 128 kbps is plenty for speech and 192 kbps for music. M4A (AAC) is the native format on Apple devices and sounds a little better at the same bitrate. OGG Opus gives the smallest files for speech. WAV keeps the joined audio uncompressed for further editing but is about ten times larger. The expected size is shown before you merge.

Files are joined top to bottom: use the up and down buttons to arrange them, and the numbers show the final order. Name files with a leading number (01, 02, 03) before adding them and they usually arrive in the right order already. The merger doesn't change the loudness of each file, so if one recording is much quieter than the others it will stay quieter in the result; recordings made with the same device and settings join most naturally. To remove a bad take from one of the files first, use the Audio Cutter, and to drop silence at the start or end, use the Audio Trimmer.

Your files are decoded and joined by your browser's own media engine and encoded on your device — MP3 with the open-source LAME encoder — so nothing is uploaded. The audio is processed in small pieces, so even long recordings don't need much memory; only the few seconds of a crossfade are held back at a time. Files are checked by their content, so a renamed document is refused with a clear message.