How are 5.1 channels mixed into stereo?

Left and right pass straight through, the centre feeds both legs, the left surround feeds the left leg and the right surround the right leg. Each contribution is scaled by a coefficient and by the fader you set, then summed into a two channel file.

What coefficients does the downmixer use?

The centre and the surrounds are folded at 0.707, and their faders start a further 3 dB down. Left and right start at unity. These are the tool's own defaults, not a certified Dolby, ITU or broadcast downmix.

Is the LFE included in the stereo downmix?

No. A channel assigned the LFE role contributes nothing, and its fader starts closed. If your material relies on that low end, assign the channel the C, L or R role and set its level by hand.

Why is dialogue quiet after the downmix?

Dialogue lives in the centre channel, which is attenuated before being summed. Raise the centre fader a decibel or two and listen again on a small speaker.

Which surround layouts can be folded down?

Anything from three channels up: LCR, quad, 5.0, 5.1 and 7.1. The output is always a two channel left and right file.

Is my surround file uploaded anywhere?

No. Your audio file is decoded, folded down and encoded locally in your browser; the media itself is not sent to a server for processing.

Workflow guide | 5 min read

How to downmix 5.1 surround to stereo, step by step

A 5.1 to stereo downmix is not six channels with four deleted. Centre, surrounds and, if you want it, LFE are folded into a two channel left and right pair with a gain for each one. This guide walks the surround to stereo workflow, from channel identification to the stereo deliverable.

Open the tool: Surround Downmixer

Watch the video tutorial

Downmix 5.1 to Stereo

1. Import and check the channel order
Load the surround master and confirm which channel is which.
- Drop a WAV, AIFF, FLAC, MP3, M4A or OGG file with at least three channels: LCR, quad, 5.0, 5.1 or 7.1.
- Each channel gets a role from the assumed film order, L R C LFE Ls Rs for six channels, and from the track names written by the recorder or DAW.
- Read the waveform of each channel and change any role from its dropdown when the source uses a different 5.1 channel order.
Tip A wrong channel order sends dialogue into a surround leg. If the channel order itself is wrong in the file, fix it with the channel mapper before downmixing.
2. Set the downmix gains
The matrix is fixed, the per channel fader is yours.
- The matrix used is Lo = L + 0.707 × C + 0.707 × Ls and Ro = R + 0.707 × C + 0.707 × Rs, with the rear channels of a 7.1 bed folded like the surrounds.
- Centre and surround faders open at −3 dB on top of that 0.707 coefficient, L and R open at 0 dB, and the LFE fader opens fully closed.
- Lift the centre fader when dialogue sits too low against music and effects; pull the surrounds down when reverb makes the stereo feel distant.
- A channel set to the LFE role contributes nothing at all. To fold low end back in, give that channel the C, L or R role instead and set its own level.
3. Preview and export the stereo
A downmix is one stereo file, so audition it before you export.
- The Lo/Ro preview plays the fold down you have set, with its own level and pan per leg, and those settings are baked into the export.
- Watch the peak warning: summing several channels into one leg can push the pair above 0 dBFS. Trim a fader rather than letting the export clip.
- Choose the output format and sample rate; free exports are WAV, Pro adds AIFF and MP3.
- Keep the source sample rate and bit depth so the stereo drops back on the same timeline, then export the two channel file.
4. Quality control
Judge the downmix on the worst speaker you can find.
- Check dialogue intelligibility on laptop speakers and on a phone, not only on monitors.
- Compare the loudness of the stereo version with the 5.1 master against your delivery target.
- Verify channel count, rate and bit depth in the Audio Inspector before delivery.
- Name the output with a stereo suffix so it never gets confused with the 5.1 master.

Frequently asked questions

How are 5.1 channels mixed into stereo?: Left and right pass straight through, the centre feeds both legs, the left surround feeds the left leg and the right surround the right leg. Each contribution is scaled by a coefficient and by the fader you set, then summed into a two channel file.
What coefficients does the downmixer use?: The centre and the surrounds are folded at 0.707, and their faders start a further 3 dB down. Left and right start at unity. These are the tool's own defaults, not a certified Dolby, ITU or broadcast downmix.
Is the LFE included in the stereo downmix?: No. A channel assigned the LFE role contributes nothing, and its fader starts closed. If your material relies on that low end, assign the channel the C, L or R role and set its level by hand.
Why is dialogue quiet after the downmix?: Dialogue lives in the centre channel, which is attenuated before being summed. Raise the centre fader a decibel or two and listen again on a small speaker.
Which surround layouts can be folded down?: Anything from three channels up: LCR, quad, 5.0, 5.1 and 7.1. The output is always a two channel left and right file.
Is my surround file uploaded anywhere?: No. Your audio file is decoded, folded down and encoded locally in your browser; the media itself is not sent to a server for processing.

Keep going

Fix the channel order first Check the layout with the Audio Inspector Open the 5.1 to stereo downmixer

No plugin, no DAW, no upload

Run this workflow on your own files

Open the tool

1. Import and check the channel order

2. Set the downmix gains

3. Preview and export the stereo

4. Quality control

Frequently asked questions

Keep going

Run this workflow on your own files