Put 2 to 20 audio files in order, add a crossfade if you like, and save one MP3 or WAV.
To join audio files, this tool decodes each one into raw samples in the order shown, places them one after the other, optionally overlaps each join with a crossfade, and saves the result as one MP3 or WAV. The browser's Web Audio decoder reads every format it can play, so MP3, WAV, M4A, OGG and FLAC files can be mixed in one job. Files are added to the end of the joined sound one at a time, so only the joined sound, the file being added and the next joined sound are in memory at once. If any file is stereo the result is stereo, and a mono file plays from both sides. A worked example: files of 180, 200 and 240 seconds with a 2 second crossfade give 620 - 2 - 2 = 616 seconds, which is 10:16. Order is the list order: drag a row, or use its up and down buttons.
A crossfade overlaps the end of one file with the start of the next while the first fades out and the second fades in. You can choose none, 0.5, 1, 2, 3 or 5 seconds. Each frame of the overlap is the first sound times cos(t x pi / 2) plus the second times sin(t x pi / 2), where t runs from 0 to 1 across the overlap. That is an equal-power curve: the two weights always add up to the same power, so two unrelated sounds keep a steady loudness through the join. Two identical sounds add up to about 3 dB louder in the middle. The overlap is cut down to half the length of the shorter file, so a 5 second crossfade between a 4 second jingle and a song becomes 2 seconds, and the result tells you when that happened. With None the files are joined with no gap and no overlap, and any silence at the start or end of a file stays.
Save as MP3 at 128, 192, 256 or 320 kbps constant bitrate, or at a variable quality, or as 16-bit WAV. Joining decodes the files first, so MP3 and other compressed inputs are compressed again when you save an MP3, and the result is not lossless; WAV adds no lossy compression, but a file with a different sample rate from the first one is resampled to the first file's rate before joining. Each file can be up to 100 MB and 30 minutes, and the joined sound up to one hour. Memory is the usual limit: joining needs about two copies of the sound, which fits about 11 minutes of 48 kHz stereo on a computer and about 5 minutes on a phone or tablet, and mono fits about twice that. If a file would pass the limit, the tool says so and nothing is made. You can join up to 20 files at a time.
It does not trim, change speed, match volume between files or choose a different crossfade for each join. To cut a file first, use the MP3 cutter. Titles, artist names and cover art in the source files are not carried over, because the files are decoded to samples and written again. The file played back under the result is the file you download, so listen to the joins before you save it.
Add the MP3 files, put them in the order you want, leave the crossfade on None for a plain join, keep Save as MP3 at 192 kbps and press Join. You get one MP3 named after the first file, such as intro-joined.mp3.
Drag a row up or down, or press the up and down buttons on it, which also work from the keyboard and on a touch screen. The list order is the play order, and the result is named after the first file in the list.
Choose 0.5, 1, 2, 3 or 5 seconds under Crossfade between files. The end of each song fades out while the next fades in. A crossfade is never longer than half of the shorter file, and the result row says if it was shortened.
Joining holds about two copies of the sound in your browser's memory. 48 kHz stereo fits about 11 minutes on a computer and about 5 minutes on a phone or tablet, mono about twice that, and the result can never pass one hour.
Saving MP3 compresses the sound again, so there is a small loss from compressing twice, more at 128 kbps than at 320 kbps. Saving WAV adds no further loss, but the file is large: about 10 MB for each minute of stereo at 44.1 kHz.
No. The files are read and decoded in your browser, joined in this tab's memory and written there, and no server receives them. The crossfade, format and bitrate are saved in this browser. The page counts visits with Google Analytics, never file names or sizes.