In this article, Eli Krantzberg puts Sound Radix’s new, and much revered, Auto Align 2 automatic phase alignment plugin to the test on a multi mic drum recording. Check out the video to see it in action…
Brief Summary
Recording a musical instrument or group with multiple microphones has inherent comb filtering and phase problems that result from the same sound arriving at the different microphones at different times. Sound Radix's Auto Align 2 is an elegant, one-button solution to this age-old problem, that was previously dealt with using tools hardly very far ahead of "stone knives and bearskins."
Going Deeper
I've been multi-track recording drums for over fifteen years now, and pride myself on getting a pretty decent drum kit sound. I've followed all the conventional wisdom about measuring an equal distance between the overhead and snare mics, and the floor tom and snare mics. Flipping the phase of the overheads, and so on. And it all worked pretty well. Or so I thought.
The fundamental problem with a multi-mic'd drum kit is that it is inevitable that the sound from the various drums will reach the different mics at different times. The more mics, the worse it is. The problem with this is that if you have duplicate signals a millisecond or two apart from each other, some of the frequencies will cancel out. This results in a thinner sound. The full-fidelity captured by the microphones is compromised. And this is only half the problem.
Even if the time delay is compensated for by manually shifting the tracks around or using sample delay plug-ins with values arrived at by calculating the exact distances of the microphones from each other, there is the problem of phase as well.
Waveforms all have peaks and valleys. When they are out of phase, the peaks from the multiple microphones don't all line up in the same position within the wave. Flipping the phase is a pretty blunt tool to correct this. It merely inverts it 180 degrees. That's great if the signals are perfectly out of phase with each other. But they rarely are. At best, flipping the phase merely reduces the amount of filtered frequencies. The combination of the timing and phase offsets results in potentially deep notches within the frequency spectrum; often referred to as comb filtering. That is why kick drums and snare drums often sound thinner than they ultimately should and could.
I'm new to Auto Align 2. I've never used its predecessor, so can't compare the ease of use between the two versions. What I can say, is that it took me a total of about fifteen seconds before I had to pick my jaw up from the floor. It's simply not possible to know what you have been missing until you hear your multiple tracks perfectly time and phase aligned. There's no going back. I don't plan on ever doing another drum track without this process in place to ensure I am getting the most phase and time-accurate response possible.
In this video, after a short clinical example to demonstrate the effects of the comb filtering that happens with multiple microphones on a single source, you will see and instantly hear how the sound of the drum kit opens up, like magic, after simply pressing the single "align" button in Auto Align 2. Sure, there's more to the plug-in than just that one button. You can create multiple groups for multiple multi-mic'd instruments, make manual adjustments and more. But I doubt I'll be needing those. Sound Radix developers - you had me at "align". Even if that was the only function in the entire plug-in; I'd still be saying "Shut up, and take my money."