Merge audio tracks so they play at the same time
The Audio Merger mixes several audio tracks into one file so that they play together — a voice-over on top of background music, a guitar layered over a backing track, or ambient sound under a narration. Each track gets its own volume, start time and optional loop, and auto-ducking can lower the music automatically whenever someone speaks.
This is different from the Audio Joiner, which plays files one after another. Use the joiner to put songs or recordings in a row; use this merger to stack them on top of each other.
Mixing happens entirely in your browser: tracks are decoded, mixed and encoded on your own device, and nothing is uploaded. You can export MP3, M4A (AAC), WAV, FLAC or Ogg; the engine is the open-source Mediabunny library (MPL-2.0), with the LAME (LGPL) and libFLAC (BSD) encoders loaded only for MP3 and FLAC.
How to use the Audio Merger
- Drop two or more audio files on the box (up to eight). The first becomes the Voice track and the others Music; change any track’s Role if needed.
- Set each track’s Volume and Starts at time — or drag its lane sideways on the timeline — and tick Loop to fill the mix for short music beds.
- Choose the Mix length and an optional fade-out at the end.
- Leave Auto-ducking on to dip the music under speech, and choose how far it dips and how quickly it comes back.
- Keep the Master limiter on, choose an output format and press Mix tracks. Listen to the result, then download it.
Audio Merger features
Per-track volume, start and loop
Volume from 0 to 200 %, a start offset in seconds (or by dragging the lane), and looping so a 30-second jingle can run under a 10-minute talk.
Automatic ducking
The voice level is measured every 10 ms. When it rises above the threshold the music dips by 6–24 dB, starting 100 ms early so the first word is clear, and recovers smoothly after a short hold.
Master limiter
A look-ahead peak limiter keeps the mix at or below −1 dBFS, so loud moments are turned down smoothly instead of clipping.
Any formats and sample rates
Mix an MP3 voice note with a 48 kHz WAV and a FLAC; tracks are resampled with a windowed-sinc filter to one rate before mixing.
Timeline with lanes
Every track has its own lane showing its waveform, start, loops and ducked passages; zoom in to line up an entrance exactly.
Fade-out and length control
End the mix with the longest track, the voice, the shortest track or an exact length, with a smooth fade-out of up to 60 seconds.
How much should the music be ducked?
Ducking is measured in decibels (dB). Every 6 dB of reduction roughly halves the music’s amplitude: −6 dB leaves it at 50 %, −12 dB at 25 % and −18 dB at about 12.5 %. For a podcast or tutorial with talking over music, −12 to −18 dB keeps the music present but out of the way. For a video where the music matters, try −6 to −9 dB.
The Voice detected above threshold decides what counts as speech. A clean voice recording is usually far louder while talking than between sentences, so the default of −40 dB suits most recordings. If breaths or room noise trigger ducking, raise it to −35 or −30 dB. Music returns over sets the release: short values pump between words, long values keep the music down through short pauses.
Getting a clean mix
- Keep voice at 100 % and start background music at 30–50 %; adjust by ear with the result player.
- Trim the music first with the Audio Cutter so the loop point falls on a beat, and add a gentle end with Audio Fade Out if you export it separately.
- Volumes above 100 % add gain; with several loud tracks the limiter will work hard, so lower the music rather than pushing the voice.
- To put the finished mix under a video, use Add Audio to Video.
Audio Merger FAQ
How do I add background music to a voice recording?
Drop the voice recording and the music file here. Keep the voice track’s Role as Voice and the music as Music, set the music volume to about 40 %, tick Loop if the music is shorter, leave Auto-ducking on and press Mix tracks.
What is the difference between merging and joining audio?
Merging (mixing) plays tracks at the same time, layered on top of each other. Joining plays them one after another. For joining, use the Audio Joiner.
Is this audio merger free and private?
Yes. It is free with no sign-up or watermark, and your audio never leaves your device — all mixing is done in your browser.
What is auto-ducking?
Auto-ducking automatically turns background music down while a voice is speaking and back up in the pauses, the way radio presenters talk over music. Here it follows the level of every track marked as Voice.
Why is my mix quieter than I expected?
The master limiter keeps peaks at −1 dB. If loud tracks overlap, it reduces the level at those moments. Lower the background music or turn the limiter off if you prefer to set levels yourself — but then watch for clipping.
How many tracks can I mix?
Up to eight. All tracks are held in memory while mixing, so long tracks need a device with plenty of free memory.