19 May 2026 | 6 min read
5.1 to stereo: the LoRo downmix explained
Every 5.1 mix eventually needs a stereo version. Doing it by simply summing channels is how dialogue gets buried and peaks go red.
A downmix folds a multichannel mix into fewer channels. The standard approach in film and broadcast is LoRo, short for Left only / Right only, which keeps the stereo image predictable and keeps dialogue intelligible.
The LoRo matrix
In its classic form: Lo = L + 0.707 x C + 0.707 x Ls, and Ro = R + 0.707 x C + 0.707 x Rs. The 0.707 factor is -3 dB, which preserves acoustic power when a signal is spread across two outputs rather than one.
- L and R: unity gain, 0 dB.
- C: -3 dB into both sides, keeping dialogue centred and audible.
- Ls and Rs: -3 dB, often lower if the surrounds are effect-heavy.
- LFE: usually discarded entirely.
Why the LFE is dropped
The LFE is not a bass channel of the mix, it is a separate effects send with its own gain structure, typically +10 dB in the monitoring chain. Folding it into stereo produces boomy, distorted low end. Leave it at minus infinity unless someone specifically asks for it.
Watch the peaks
Adding three signals together can easily exceed 0 dBFS even when each source is well behaved. Check the resulting peak before export, and pull a global trim rather than clipping. A -3 dB overall trim on the downmix is a common, transparent fix.
LoRo versus LtRt
LtRt encodes the surrounds out of phase so a Pro Logic decoder can recover them. It is the right choice for a matrix-encoded deliverable, and the wrong one for a plain stereo listening copy, where the phase tricks cause smearing on mono playback.