Q: There is a delay in my drum overheads. How can I fix it?
Here is the full question from this Audio Masterclass reader:
"I encountered a problem with my latest attempt to record drums - the snare. More specifically, the snare sounded like it had some delay in it - the time gap between the snare hit from the snare mic and the overheads was several milliseconds, so the delay was audible and irritating. How do I get rid of this? The system latencies can't be blamed (the university's Pro Tools HD 8), it's a question of mic placement - my lack of expertise. I've considered placing the overheads so that they 'hide' behind the cymbals, but then I would lose the toms from the overheads."
There is always the potential for a problem where two microphones pick up the same sound source but from different distances.
Since sound travels around 30 cm (1 foot) in one millisecond, the two waveforms will not be in the same phase, resulting in interference that will boost some frequencies and cut others.
For a drum sound this is made worse by the fact that the initial strike of the drum head is short and sharp. You don't need much of a delay for this transient to be heard twice.
If for instance the snare drum mic is almost touching the drum head, and the overheads are at a height of 1 meter above the snare, then there will be a 3.4 millisecond delay approximately, and frequencies around 170 Hz, 510 Hz and 850 Hz, and others, will cancel.
This problem is at its worst when the two signals are mixed at the same level.
There are two ways of approaching mixing drum overheads...
One is to regard the close mics as the main mics. Balance the close mics as you want them, then blend in the overheads.
The other is to regard the overheads as being the proper sound of the drums, then you would bring in the individual mics to add clarity and body as you wished.
In either case when the close mic signal from the snare is similar in level to the signal in the overheads, then the delay problem will be at its worst.
One thing we have to consider here however is that countless successful drum recordings have been made without anyone worrying about this delay. So perhaps there is another problem. Inserting plug-ins into some signal paths and not into others is a likely cause when automatic delay compensation isn't used.
Another possible cause of the annoyance factor is that you have super-sensitive ears!
But the problem is easily solved...
Simply zoom in on the waveforms and move the overheads earlier in time until they match up with the snare, or until they match all of the close mics as nearly as possible. This technique is worth experimenting with for any type of recording using multiple microphones at different distances from the sound source(s).
Let us know how you get on.