Use the free Audio Mixer Online below: mix two audio files into one track that plays both at the same time, with a volume slider for each track. Your files never leave your device.
What the Audio Mixer does
The Audio Mixer Online mixes two audio files into one track. Both tracks play at the same time, on top of each other. You get one mixed WAV file at the end, not two separate tracks.
This is different from joining audio end to end. A joiner plays one file after the other. A mixer plays both files together, so you can hear a voice over music, or two sounds at once. Each track has its own volume slider, so you can decide how loud each one is in the mix.
Everything runs in your browser. Your files are never uploaded to a server. There is no account to create and nothing to install. The tool works with common audio files your browser can play, such as WAV and MP3.
How to use the Audio Mixer
First, choose your two audio files. Track A is the first file and Track B is the second file. The tool shows the length and size of each file, plus a picture of its sound wave, so you can check you picked the right files.
Next, set a volume for each track. Both sliders start at 100 percent. If you want the music quieter than the voice, turn the music track down to 30 or 40 percent and leave the voice at 100 percent. The volumes are relative, which means only the balance between the two tracks matters.
Then press Mix audio. The tool decodes both files, lines them up at the same starting point, and renders one mixed track. When it finishes, you see the mixed sound wave, the length of the result, and its file size. Press Download mixed WAV to save it.
If the balance sounds wrong, change a slider and mix again.
Worked example: two test tones mixed together
Here is a real example run through this exact tool. Track A was a 2.0 second tone, 172.3 KB in size. Track B was a 3.0 second tone of a different pitch, 258.5 KB in size. Both volume sliders were left at 100 percent.
The mixed result was a single WAV file, 3.0 seconds long and 516.8 KB in size, at 44100 Hz with 2 channels. Three seconds is the length of the longer track, Track B. That is the rule: the output is always as long as the longer of your two tracks.
During the first 2.0 seconds, both tones are audible at the same time. That is the overlap, and it is the proof that the tool mixes rather than joins. During the last 1.0 second, only Track B is audible, because Track A has already ended and its place in the mix is silence.
Try the same idea with your own files: a short voice note over longer music gives voice plus music together, then music alone after the voice ends.
When a mixer is the right tool
A mixer is useful when two sounds belong together at the same moment. A common case is a voice recording over background music, for a video intro, a podcast opening, or a simple announcement. Put the voice on one track and the music on the other, then turn the music down so the words stay clear.
It also works for simple sound design. You can layer a rain sound under a spoken reading, or combine two sound effects for a game or a presentation.
A mixer is not the right tool when you want one sound after another. For that, use an audio joiner instead. It is also not an editor: you cannot cut or move a track to start later. Both tracks always start at the same moment.
Honest limitations
The output is WAV only. WAV files are large because they store sound without compression. A 3.0 second stereo mix at 44100 Hz is about 517 KB, and a 3 minute mix at the same settings would be about 31 MB. Keep this in mind before you download long mixes.
The two tracks are mixed into one track and cannot be separated afterwards. If you need to change the balance later, mix again from your original files. The output is also normalized only when it would otherwise clip: if the two tracks together are too loud, the whole mix is turned down just enough to avoid distortion, and the balance between the tracks stays the same.
Large files take longer to decode and mix, and very long files can use a lot of browser memory. If a mix fails, try two smaller files, or shorten them first with an audio trimmer.
Frequently asked questions
Does the mixer keep my two tracks separate? No. The output is one single track with both sounds mixed together, and you cannot split it back into the two originals.
How long is the mixed file? As long as the longer of your two tracks. The shorter track plays from the start and then becomes silence for the rest of the mix. Nothing is stretched or looped to fill the gap.
Why is the WAV file so big? WAV stores every sample without compression, so size grows with length, sample rate, and channel count.
Do my files leave my device? No. Decoding, mixing, and WAV encoding all happen in your browser on your own device. Nothing is uploaded anywhere.
Spanish version: Mezclador de Audio Online