Mix Level Sum Calculator – Combined dB of Multiple Uncorrelated Tracks

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Why you cannot just add decibels

A beginner mixing their first song often makes the same arithmetic error: two tracks at minus six decibels must add up to minus twelve, or to zero, depending on which wrong intuition they follow. Neither is right. Decibels are logarithmic, so adding them directly is like adding the exponents of numbers and expecting the sum: it does not work. The correct method converts each level back to power, adds the powers, and converts the total back to decibels. For uncorrelated tracks, which means different sounds that are not identical copies of each other, the formula is ten times the logarithm of the sum of ten to the power of each level divided by ten. This calculator does exactly that, and it also shows the coherent case, where identical in-phase signals add differently.

The difference between the two cases is worth understanding, because it explains many mixing surprises. Two identical tracks, perfectly in phase, double the amplitude, which is an increase of six decibels. Two different tracks at the same level, such as a guitar and a keyboard, double the power but not the amplitude, which is an increase of about three decibels. In a real mix, most track combinations sit near the uncorrelated case, because each instrument plays different notes at different times. Even two microphones on the same guitar are only partly coherent, so the real increase falls between three and six decibels depending on phase. The calculator gives you both endpoints, so you can plan for the range rather than guessing a single number.

How to use the calculator

1. List the level of each track in decibels, separated by commas. Use peak levels together, or RMS levels together, but do not mix the two.
2. Choose uncorrelated for a normal mix of different sounds, or coherent for identical in-phase copies.
3. Read the combined level, the loudest single track, and how much the combination adds over that loudest track.
4. Compare the combined level with your ceiling to see how much headroom remains.

A worked example

Take four tracks at minus six, minus nine, minus twelve and minus eighteen decibels. Converting each to power, adding, and converting back gives a combined level of about minus three decibels. The loudest track alone is minus six, so the other three tracks together add about three decibels. That is a typical mix result: the loudest few tracks dominate, and quieter tracks add surprisingly little. Add a fifth track at minus thirty decibels and the total barely moves, by less than a tenth of a decibel, because its power is a tiny fraction of the total. This is why turning down a quiet track rarely fixes a clipping mix bus: you must turn down the loudest tracks, or the bus itself, to make a real difference.

Using the sum to plan a mix

Before you start mixing, you can use the sum to set sensible starting levels. If eight tracks at minus twelve decibels each combine to about minus three decibels, you already know the bus will sit near the ceiling before you add any processing, so start lower, perhaps at minus eighteen per track. If you add a loud vocal on top of an already full instrumental, expect the bus to rise by one to three decibels, not by the vocal level alone. Leave that rise in your plan. Many engineers mix with the master fader at unity and each track peaking well below zero, precisely because they know the sum will lift the total. The calculator turns that habit into a number you can check before you touch a fader.

Limits of the calculation

This sum assumes the levels you enter are measured the same way, over the same moment in time. In a real song, tracks peak at different moments: the drum peaks when the vocal is quiet, and the vocal peaks between drum hits, so the true bus peak is usually lower than the sum of individual peaks. That is good news, but it also means the calculator gives a worst-case, all-peaks-at-once estimate, which is the safe number to plan with. It also ignores phase cancellation, which can reduce the sum, and frequency masking, which affects perceived loudness more than measured level. Use the result as a planning ceiling, listen to the real mix, and trust the meter on the bus for the final word. The math tells you what to expect; the meter tells you what actually happened.

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