Welcome back to Sound Advice on Recording Drums! In previous installments, Michael Schulze has described in detail why you should consider time-aligning drums that were recorded with microphones located at varying distances from the elements of the drum kit. Now we start to explain how it’s done!
For our time-aligning example we will use a drum kit that was recorded with seven mics: two overhead mics, one mic in front of the kick drum, one mic each on two rack toms, one mic on the hi-hat, and one mic over the snare.
The overhead mics have been placed to pick up mostly cymbals, but they pick up plenty of snare and toms and also some leakage from the kick drum. We are going to delay all the close mics to match their timing with that of the overheads, to eliminate frequency cancellations and additions from all this leakage.
To calculate the needed delay times from scratch simply measure the distance in feet from each mic to the nearest of the two overhead mics. Then divide this distance by the speed of sound in feet per second (1136). We’ll use the snare as an example.
The snare-drum mic is closest to the right overhead mic, at a distance of 2 feet, 6 inches (2.5 feet). 2.5 divided by 1136 equals about 0.002 seconds, which is 2 thousandths of a second or 2 milliseconds. If you have no calculator, no pencil, or you are hung over, or just dumb (like me), you can round it out to 1 millisecond per foot and still get pretty good results! So now you need to delay the snare channel by 2.5 milliseconds.
Let’s assume your session is over and you are in the mixing stage. Digital mixers usually have an easily accessible delay parameter on each track, as does most modern DAW software. You will need to make sure you set the delay so that you are hearing just the delayed signal with no direct signal. Alternatively, you can slide the tracks around by hand to line them up by eye.
Check out the Digital Performer screen shot below (from an older version, but the information is still useful). It shows the mono snare track and the stereo overhead track. I’ve selected a spot in the tune where the snare was hit pretty hard and nothing else in the drum kit is being hit. This is very important! You can clearly see the time delay between the snare track and the waveform of the snare leakage in the overheads.
You might have to find a way in your DAW to turn off Grid Edit (or whatever your DAW calls it when it snaps edits to a fixed time grid). This should allow you to slide your audio around freely. Now pick a spot that is close to identical on the two tracks. I find that zero crossings work best, and I have indicated two such zero crossings in the screen shot above.
You can easily see the similarity between the two spots, which tells you that you are looking at the same sonic event in the two tracks. Select the entire snare track. (A surefire way to do this is to press Command-A (Select All) and then Command-Click on the track name in the Sequence window.) Now carefully slide the entire snare track to the right until the waveforms match up like this:
If you have done this in one step you can quickly compare the sound by pressing Command-Z (Undo) to put the audio temporarily back to its original position. If you have done this right you will almost certainly hear a striking difference between the two situations, with the time-aligned version sounding more solid and with a clearer stereo image. Switch it back and forth a few times if you can’t tell at first. Once you focus in on the difference it will get easier to hear and you will have a hard time going back to the old way!
You can then proceed to the other tracks, but when you get to the kick you’re going to run into trouble. We’ll talk about this next time. See you then!