Merge Audio Files

Most online joiners do one thing: they decode everything, glue it together and re-encode it. This one starts by checking whether it needs to decode anything at all.

• A lossless join. When your tracks already share a codec, a sample rate and a channel count, the encoded audio is copied into the new file untouched. No decode, no encode, no generation loss — and it finishes in milliseconds rather than seconds.
• Three ways for tracks to meet. Butt them together with no gap, insert an exact amount of silence, or crossfade one into the next. Gap and crossfade are the same control, because they are the same axis in opposite directions.
• Per-track trim and level. Cut the dead air off the front of track three and lift track five by 4 dB, in the same pass as the merge. No round trip through a separate cutter.
• Fades where they belong. A fade in on the first track and a fade out on the last, applied to those tracks rather than bolted onto the finished file.
• One loudness for the whole result. Match the merged track to -14, -16 or -23 LUFS with a two-pass measurement, so a quiet interview and a loud jingle end up at the same level.
• A chapter list. The start time of every track, as plain timestamps, ready for show notes or an audiobook description.

Audio in a file is already encoded. Joining two MP3s does not require understanding the sound inside them — it only requires writing one set of encoded frames after the other. When that is possible, this tool does it, and the result is mathematically identical to the sources rather than merely close.

It happens when all of this is true

• Every track uses the same container and the same codec.
• Every track has the same sample rate and the same channel count.
• The output format you asked for is the one the tracks already are.
• No crossfade, no gap and no fade.
• No trim and no level change on any track.
• No loudness matching, band filter, dynamics or silence trimming.

The rail tells you which of the two is about to happen before you press anything. If you turn one effect on, the line changes — because asking for an effect means asking for a re-encode, and a tool that claimed otherwise would be lying about what it just did to your audio.

One file is easier to publish, easier to send and easier to listen to than five. A merged track also plays without the pause a player inserts between separate files, which matters for a continuous mix or a chaptered recording.

What it is good for

• Podcast episodes: join an intro, the interview and an outro into one publishable file
• Audiobooks: combine chapters with an exact pause between them and keep the timestamps
• DJ-style mixes: crossfade tracks so one blends into the next with no silence
• Voice recordings: stitch takes together and trim the fumbles out as you go
• Sample packs: concatenate short clips into a single file for easier transfer

How two tracks meet is the decision that most changes how a merge sounds, and it is one control rather than three because a gap and a crossfade are opposite directions on the same axis: positive space between tracks, or negative space where they overlap.

• Gapless: the next track starts on the sample after the last one ends. Right for an album side, a continuous mix, or anything already edited to butt together.
• Gap: an exact amount of silence is inserted between every pair, in tenths of a second up to ten. Right for chapters and for spoken segments that need a breath between them.
• Crossfade: the end of one track and the start of the next overlap and fade through each other. Right for music. The merged result gets shorter by the crossfade length for every join, which the duration readout already accounts for.
• Fade in and fade out: applied to the first and last tracks, so a mix can rise out of silence and settle back into it.

The crossfade slider will not offer a length the files cannot carry. A crossfade eats into both neighbours, so its ceiling is half the shortest track you have loaded — and that ceiling moves when you add, remove or trim a track.

The format decides two things: where the result will play, and whether the join can be lossless. Picking the format your sources already are is what unlocks the copy path.

• MP3: plays on everything ever made. The safe default for a podcast or a mix you are sending to someone.
• M4A: AAC in an MP4 container. Better sound than MP3 at the same size, and the format Apple devices and audiobook players prefer.
• AAC: the same audio as M4A without the container. Useful for streaming pipelines that expect a raw bitstream.
• OGG: Vorbis in an Ogg container. Open, patent-free, widely supported on Linux and in games.
• FLAC: lossless and about half the size of WAV. The right choice for archiving a merged master.
• WAV: uncompressed and universally editable. Large, but nothing at all is thrown away.

Five steps, and the tool tells you which path it is about to take before you commit to it.

1. 1Add your audio filesDrop in MP3, M4A, AAC, OGG, FLAC, WAV, or a video file you only want the audio from. Every file is read on your device and none of them is uploaded.
2. 2Put them in orderDrag a track by its handle, or use the move buttons. The track at the top plays first. Trim the start and end of any track, and lift or drop its level, without leaving the page.
3. 3Choose how the tracks meetGapless butts them together, a gap inserts an exact amount of silence between them, and a crossfade blends each track into the next. Add a fade in on the first track and a fade out on the last.
4. 4Pick the outputMP3 plays everywhere, M4A suits Apple devices, FLAC and WAV stay lossless. When every source already uses the codec you have asked for, the tracks are copied through rather than re-encoded.
5. 5Merge and downloadPress Merge, listen to the result, then download it. The chapter list beside it gives you the start time of every track, ready for show notes.

Most merges go wrong in one of a small number of ways, and all of them are avoidable before you press the button.

Worth doing

• Ask for the format your sources already are if you want the lossless path — the rail says which path you are on before you run anything.
• Order the tracks before you trim them; the trim belongs to the track, not to the position.
• Turn on loudness matching when the sources were recorded on different days or different devices.
• Use a gap rather than a crossfade for anything with speech in it — a crossfade over a word swallows it.
• Listen to the merged result before downloading, especially around each join.

Common jobs

• Interview plus intro: trim the leader off the interview, add a one-second gap, match loudness
• Continuous mix: crossfade three seconds, fade in the first and out the last
• Chapter assembly: gap of one second, then keep the chapter list for the description
• Archive master: FLAC out, no effects, sources already FLAC — copies through untouched

Two paths, chosen automatically from what you have loaded and what you have asked for.

The two paths

• The copy path: the encoded frames of every track are written into one new container in order. Nothing is decoded and nothing is re-encoded, so the audio that comes out is bit-for-bit the audio that went in.
• The rebuild path: every track is decoded, trimmed, levelled, faded and brought to a common sample rate and channel count, then joined and encoded once. One encode, never one per track — a chain that re-encoded at each step would lose a generation per join.
• Loudness, measured twice: when loudness matching is on, the whole merged result is measured first and then corrected with a single computed gain. A one-pass normaliser adapts as it goes and misses its own target; measuring first lands on it.
• Order of operations: silence trimming and level changes happen per track, before anything is joined; band filtering and loudness happen after, on the finished result — because removing rumble changes how loud something measures.

Merging runs entirely on your device. A ten-track lossless join finishes in well under a second because nothing is decoded at all.

Every capability is on the free plan, including the crossfade, the per-track trim and the lossless join. What Pro raises is scale and the mastering controls.

• Free: up to 10 tracks, 50 MB per file, 10 minutes of combined output, and output up to 44.1 kHz. All six output formats, all transitions, all per-track controls.
• Pro: up to 50 tracks, no fixed size or length ceiling beyond what your own device can handle, higher sample rates, and the mastering block — loudness matching, band presets, dynamics and silence trimming.

• Merge MP3 Files
• Merge WAV Files
• Merge OGG Files
• Merge M4A Files
• Merge FLAC Files
• Merge AAC Files

• Audio compressor
• Audio cutter
• Audio splitter
• Loudness normalizer
• Audio converter
• Fade audio