Spaced overheads are typically placed so that they are equidistant from the centre of the snare’s batter head — but there will always be differences in the distance from other kit pieces.
For miking the drum kit in my home recording studio, I’m using two Audix ADX51s as overheads. After running some samples, I can see that there is a very slight difference in the alignment of the waveforms between the left and right microphone (which I think experts call a ‘phase issue’!). My question is, what are the typical tolerances (say, in milliseconds) for acceptable differences between a pair of overheads like this?
Obviously it would be nice to have it all perfect, but do you have any thoughts on what’s reasonable to accept before you need to start looking at tweaking the audio files to realign them digitally in your DAW? I’m using Cakewalk. Perhaps there are some benchmarks for what the human ear can detect that might be useful to know?
SOS Forum post
SOS Technical Editor Hugh Robjohns replies: If the mics are in different places, then sounds from different sources will reach them at different times because the distance between, say, the floor tom and each mic is slightly different. So some timing differences are to be expected in overheads, and contribute to the stereo spread.
Some timing differences are to be expected in overheads, and contribute to the stereo spread.
The usual practice is to make sure the overheads are exactly the same distance from the centre of the snare batter head. This makes sure that the sound of the snare reaches both mics simultaneously, and thus the snare sits in the centre of the stereo image. In terms of offset tolerances, a timing difference of 1.5ms is enough to make the earlier sound appear to be fully to one side of the stereo image.