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Stereo mono fold-down
Estimate RMS amplitude when left and right channels are summed or averaged for mono playback.
Left RMS level (dB re reference): -120–0; Right RMS level (dB re reference): -120–0; Correlation coefficient: -1–1
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Stereo mono fold-down
Left RMS level (dB re reference): -18 Right RMS level (dB re reference): -18 Correlation coefficient: 0
- L+R RMS (× reference)
- 0.178039
- (L+R)/2 RMS (× reference)
- 0.089019
Let a = 10^(L/20), b = 10^(R/20) and correlation r. Sum RMS = √[(a−b)² + 2ab(1+r)]; averaged mono RMS = sum/2. Inputs use the same RMS amplitude reference, with 0 dB equal to amplitude 1, not a peak or a full-scale-sine calibration. Enter −120–0 dB per channel and r from −1 to +1, including fractions. Outputs are linear RMS amplitude multiples, not dB or peak levels. Equal channels cancel at r = −1; averaging identical channels at r = +1 retains their level. Use levels and correlation measured over the same time window and bandwidth on zero-mean signals. This does not measure an audio file, predict sample peaks, clipping, loudness, frequency-specific cancellation or guarantee mono compatibility. Real mixers may use other summing gains. Six decimals, no intermediate rounding.
Methodology
How it works
Let a = 10^(L/20), b = 10^(R/20) and correlation r. Sum RMS = √[(a−b)² + 2ab(1+r)]; averaged mono RMS = sum/2. Inputs use the same RMS amplitude reference, with 0 dB equal to amplitude 1, not a peak or a full-scale-sine calibration. Enter −120–0 dB per channel and r from −1 to +1, including fractions. Outputs are linear RMS amplitude multiples, not dB or peak levels. Equal channels cancel at r = −1; averaging identical channels at r = +1 retains their level. Use levels and correlation measured over the same time window and bandwidth on zero-mean signals. This does not measure an audio file, predict sample peaks, clipping, loudness, frequency-specific cancellation or guarantee mono compatibility. Real mixers may use other summing gains. Six decimals, no intermediate rounding.
Method and assumptions documented by Techrider.live
2026-11-03
Frequently asked questions
Why show both a sum and an average?
An unattenuated L+R sum doubles identical in-phase amplitudes. Dividing by two preserves their original amplitude. Check the actual mono-bus gain and listen to the result.