Free Audio Joiner

Worked example

Press "Try a sample". Two copies of sample-melody.wav appear, each 0:01.9 long, and "Total length" reads 0:03.8. The format is MP3 at 192 kbps, so "Estimated size: 89.1 KB" shows beside "192 kbps MP3". Drag "Silence between tracks" to 1s: the hint reads "Adds 1s of silence after each track.", the total becomes 0:04.8 and the estimate 112.5 KB. Press "Join 2 files". The page shows "Joined 2 files" with the size and a "Download" button, and the file is named sample-melody-joined.mp3. Under "Track timestamps" the list reads "0:00 sample-melody" and "0:02 sample-melody", because the second track starts at 2.9 seconds and the list drops the tenths. With "Crossfade between tracks" at 1s instead, the total is 0:02.8 and the second track starts at 0:00.

Which settings to use, and the limits

• Set the order before you join. Drag a row by its handle, or use the up and down arrows. With two or more tracks a "Sort tracks" row appears with "A–Z", "Z–A", "By number", "Oldest first", "Newest first" and "Reverse". Files you add in one go are first put in natural order, so "Recording 2" comes before "Recording 10", because phones often return a multi-selection in no set order. Later additions go to the end of the list. "By number" sorts on the first number in each file name. The play button plays one track at a time, from its trim start to its trim end.
• Trim and fade each track on its own. The "Trim & fade" button (a scissors icon on narrow screens) opens a waveform with two handles; arrow keys move one by 0.1 s, or 1 s with Shift. The "Start" and "End" boxes take times like 1:05.5. "Use playhead" copies the position of the track you are previewing, so press play on that track first. "Fade in (seconds)" and "Fade out (seconds)" accept 0 to 30 in steps of 0.5. The waveform is drawn only for files up to 40 MB; larger files get a plain sketch, though the boxes still work. A fade-out needs the track's length, so set an End time if it is unknown.
• Choose a crossfade or a silent gap. "Crossfade between tracks" runs from 0 to 12 seconds in steps of 0.5 and blends the end of one track into the start of the next; each track must be longer than the crossfade. "Silence between tracks" runs from 0 to 5 seconds in steps of 0.5 and is switched off while a crossfade is on. "Fade shape" offers "Linear", "Equal power" and "Exponential" and applies to every fade; the page says Equal power sounds smoothest for crossfades. Inside "Trim & fade", "Hear the join with the next track" plays the last 3 seconds of one track into the first 3 seconds of the next.
• Pick a format, then a size target for sharing. "Output format" offers MP3, M4A, OGG, WAV and FLAC. For the three lossy ones, "Audio quality" offers 32, 48, 64, 96, 128, 192 (the default), 256 and 320 kbps. "Target size" offers "Email (25 MB)", "WhatsApp (16 MB)" and "Custom". It picks the highest of those bitrates whose estimate fits, counting 1 MB as 1,000,000 bytes and keeping 3 percent spare. For one hour of audio, Email gives "Using 48 kbps, the best quality that fits 25 MB." If even 32 kbps is too big, you get "Even the lowest quality is over 25 MB for this length. Trim tracks, use mono, or raise the limit."
• Match loudness when tracks differ. The page measures each track (files up to 40 MB) and, when one is more than 6 dB from the typical level, shows a line such as "About 9 dB quieter than the other tracks. Turn on “Match loudness” below." "Match loudness" brings every track to the same volume before joining, aiming at −16 LUFS, and the hint warns that it takes a little longer. "Mono" mixes to one channel and halves the file size; the page says it suits voice and lectures, while music loses its stereo width. Otherwise the output is stereo if any track is, at the highest sample rate among your tracks.
• Name the file, add tags and keep a track list. The "File name" box takes up to 120 characters and adds the extension for you. Under "Title, artist and cover (optional)" you can set Title, Artist and Album; tags from your source files are not carried over. A cover image (JPG or PNG, up to 8 MB) can be added to MP3, M4A and FLAC only. After joining, "Track timestamps" lists each start time as m:ss, with "Copy", "Download .txt" and "Download .cue". The cue sheet labels the audio MP3 for MP3, AAC for M4A and WAVE for every other format.

Common problems and how to fix them

It says "“voice-note.m4a” has no readable audio — it may be damaged or not an audio file. Remove it and join again." (with your own file name).

Before encoding, the tool opens every track with the media engine and checks that it contains an audio stream. The first track with none stops the join and is named in the message. Remove it with the "✕" button and press the join button again. If a second file is named next, that one is unreadable too. A dash instead of a length beside a track can point to the same problem. A 0-byte file, common with cloud-drive placeholders, is refused when you add it.

It says "This conversion failed — the chosen format or codec may not be supported for this input. Try a different output format, or a different source file."

The tool picks one of a few fixed sentences from the engine's error text, and this one is used when the text mentions a failed conversion, an unsupported codec or an encoder that would not start. Try WAV, which writes plain 16-bit audio, then switch off "Match loudness" and remove the cover image. If it still fails, join fewer tracks at a time to find the one that causes it. "The encoder stopped unexpectedly." and "Something went wrong while processing this file." have the same advice.

It says "Processing cancelled." in a red box and nothing was joined.

You pressed "Cancel", which sits under the progress bar while a join runs. Cancel stops the encoder at once, so no file is produced, but your tracks, their order and your settings stay as they were. Press "Join 2 files" (or your count) again; the engine is reloaded for the next run. A join of many long tracks takes a while, so look at the percentage next to "Joining…" before you cancel.

It says "These files total 520 MB, over the ~400 MB this device can handle in the browser. Remove some or use a desktop."

The figures are the total size of all your tracks and the limit for this device: about 2 GB on a normal computer, 1 GB on one reporting 4 GB of memory or less, and 400 MB on a phone or tablet. While the total is over the limit, the Join button stays disabled. Remove tracks, or join in two rounds and then join the two results. A second round re-encodes the first, so choose WAV or FLAC for the middle step if quality matters.

It says "“intro.mp3” is not longer than the 4s crossfade after trimming. Shorten the crossfade or keep more of that track."

After its own trim, every track must be longer than the crossfade, because the blend needs that much audio. The check runs when you press the join button and names the first track that is too short. Lower "Crossfade between tracks", or open "Trim & fade" on that track and keep more of it. A 3-second jingle cannot take a 4-second crossfade. A trim whose end is not after its start gives "End must be after Start." instead.

How it compares

The Audio Joiner decodes your tracks in the browser, joins them end to end and encodes once to MP3, M4A, OGG, WAV or FLAC. MP3, M4A and OGG results are re-encoded; WAV and FLAC add no further loss. You can trim and fade each track, add a crossfade or a silent gap, match loudness and tag the result. It is not a multitrack editor: you cannot layer tracks, set a volume per track or edit inside a waveform beyond start and end points, and a desktop audio editor is the better choice for that. The total size of your files must fit the device limit of about 2 GB, 1 GB or 400 MB. In exchange nothing needs installing and the page says nothing is uploaded.