Mic Distance and Phase Calculator
See the time gap between two mics on one source, how far to move a track, and check the 3:1 guide. Free with an account.
Mic Distance Calculator is part of the Studio section of Music Manager Resource.
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Why distance matters
Sound moves at around 343 metres per second at room temperature, which is slower than people expect. If two mics pick up one source at different distances, the sound reaches the further one later. When the two are mixed, some frequencies add together and others cancel. That can make a sound thin or hollow, and it is why a drum kit or a guitar amp with two mics can sound worse than one until they are lined up.
What the numbers mean
The time gap is how much later the sound reaches the further mic. A one metre difference is about three milliseconds. The first likely dip is the lowest frequency where the two signals cancel most, if they are mixed at equal level and the same polarity. Further dips appear at higher frequencies. The samples figure tells you how far to move the further mic's track earlier in your session to line them up.
Fixing it
Start at the source by moving a mic, as a few centimetres can make a clear difference. You can flip the polarity on one channel and keep the setting that sounds fuller. You can also nudge a track in your session by the number of samples shown. Remember that real sound sources are not single points and rooms add their own reflections, so results will vary from the numbers.
The 3:1 guide
When two mics are on separate sources at similar levels, a common guide is to keep them at least three times as far from each other as each is from its own source. If a mic is 10 centimetres from a guitar amp, the next mic should be at least 30 centimetres from it. This reduces how much of each source spills into the other mic. It is a guide, not a law, and many good recordings break it.
Do you have to line everything up?
No. Those small time differences are part of how stereo recording and room mics work, and they can add depth and size. A perfectly aligned drum kit can sometimes sound smaller. Use this tool to understand what is happening, then decide by listening. Enter your units, temperature and distances, and check the result by ear.