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Audio Mixer
Layer up to four audio files into one mix: put background music under a voice-over, add sound effects, or combine instrument stems. Drag each track on the timeline, set its volume, pan and fades, listen to the mix and download it as MP3 or WAV. All processing happens in your browser.
No files handy?
Drag a waveform left or right to change when that track starts. Click an empty part of the timeline to move the playhead.
0:00.0 / 0:00.0
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How to use the Audio Mixer
- Add your tracks: drop up to four audio files (for example a voice recording and background music) or click to choose them.
- Arrange them: drag a waveform along the timeline, or type a Start at time, to set when each track begins.
- Balance the mix: set each track's volume and pan, add fades, and use M (mute) and S (solo) to check parts.
- Listen: press Play mix. Volume and pan changes are heard immediately.
- Download: choose MP3 or WAV and press Download mix.
Mixing tips for clear results
- Voice-over with music: keep speech at 100% and music at 20 to 35%. Music should be felt, not compete with words. A 1 to 2 second fade in and a 3 second fade out on the music sound professional.
- Use pan for separation: moving two similar instruments slightly left and right (for example 20% L and 20% R) makes both easier to hear. Keep voices and bass in the centre.
- Check with solo: solo a track to hear it alone, then un-solo to hear how it sits in the mix.
- Leave headroom: overlapping tracks add up. If the mix sounds harsh or crackly, lower the loud tracks rather than relying only on Prevent clipping.
- Line up beats: type exact Start at values to align music stems. At a tempo of 120 BPM one beat lasts 60 ÷ 120 = 0.5 seconds, so a bar of 4 beats is 2 seconds.
How the mix is calculated
Digital mixing is addition. For every sample of the output, the mixer adds the samples of all audible tracks after multiplying each by its volume (100% = gain 1.0, 50% ≈ −6 dB, 200% ≈ +6 dB) and applying its fade. The pan control uses an equal-power law, so a sound panned fully to one side keeps the same perceived loudness as in the centre.
| Volume setting | Gain | Change in level |
|---|---|---|
| 200% | 2.0 | +6.0 dB |
| 141% | 1.41 | +3.0 dB |
| 100% | 1.0 | 0 dB (unchanged) |
| 71% | 0.71 | −3.0 dB |
| 50% | 0.5 | −6.0 dB |
| 25% | 0.25 | −12.0 dB |
| 10% | 0.1 | −20.0 dB |
The level change in decibels is 20 × log10(gain). Two identical tracks played together at 100% are up to 6 dB louder than one, which is why the mixer can lower the final level to avoid clipping.
Frequently asked questions
What is the difference between mixing and joining audio?
Mixing plays tracks at the same time, layered on top of each other, like music under a voice. Joining (or merging) plays files one after another to make one longer file. Use this Audio Mixer to layer tracks and the Audio Joiner to put them in a row.
How do I add background music to a voice recording?
Add the voice as Track 1 and the music as Track 2. Set Mix length to Same length as Track 1 so the music stops when the voice ends, lower the music volume to about 20 to 35%, and give the music a 2 to 3 second fade out. Play the mix and adjust until the voice is easy to understand.
Why is my mix quieter or louder than the original files?
When tracks overlap their levels add up, which can push the mix above 0 dB and cause distortion. With Prevent clipping on, the exported mix is turned down just enough to keep its peaks at −1 dB. Lower individual track volumes if you want more control.
Can I mix files with different formats and sample rates?
Yes. Every file is decoded by your browser and converted to 44.1 kHz, so you can mix MP3, WAV, M4A, OGG and FLAC files with any sample rate. Mono files are placed in the centre of the stereo mix unless you pan them.
Are my audio files uploaded?
No. Decoding, mixing and encoding all run on your device with the Web Audio API, and the MP3 is created with a JavaScript build of the LAME encoder. Your files never leave your computer or phone.
How long can the tracks be?
There is no fixed limit, but the whole mix is processed in memory. Mixes up to about 30 to 60 minutes work well on most computers; phones may struggle with very long files.
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