When I recorded my drum kit for the first time, I didn’t know what I was doing. Even though I had read up a little on what to do, excitement and impatience overtook the process, and as a result, I made more than a few mistakes. The biggest was overhead microphone placement, and the phase issues that I had caused.
So how do I fix phase problems in a drum overhead mixing session? First, it is necessary to identify if you have phase issues at all. Then, phase issues can be fixed by systematically checking one microphone after another, and flipping the phase when appropriate.
Fixing phase issues in overheads, and other drum microphones can take your ‘just ok’ drum sound to another level. Understanding the way that these phase issues occur is fundamental to identifying and fixing them.
Most likely you will have a stereo pair of tracks with a left side overhead recording and a right-side overhead recording. Solo these two tracks in your mix and listen to the snare. The stereo overheads should produce a balanced sound of the whole drum kit. Decide whether you want to mix your drums as audience perspective or drummer’s perspective. Hardpan the right track right and left track left for drummers’ view.
When you listen back to the overheads, does the snare sit in the center of your mix? In most home studio setups that I have seen the computer monitor is dead center between the two studio speakers. If your snare sounds like it is coming from your computer monitor, the snare and overheads are balanced, and we can move on to looking at phase relationships.
If, however, the drum overhead tracks are not balanced, there are two options to consider:
Personally, I advocate Option 2 here as Option 1 can make things a little more complicated later on. Option 2 allows trouble-free control of the drum kit width in the mix - but more on that later on.
Now that the overheads are hard right and left panned and the snare is sitting nicely in the middle of the stereo image, we are going to double-check the phase relationship between the right and left overhead microphones. Somewhere in your DAW, on any one of several plugins, you will be able to find the Greek Phi Symbol Φ - think ‘the golden ratio’, not cherry or apple!
Figure 1: Phase Putton on Pro Tools EQIII
For consistency, I always consider my left-hand overhead as the baseline for phase relationships. I designate the left-hand overhead phase as being correct and compare the other drum tracks to this. Using a nominated track as the phase check baseline really helps with workflow.
Sound travels in waves, right? In the case of recording a snare with two overhead microphones when the drum skin is hit by the stick, the sound waves from the drum travel outward in all directions. The sound that travels to the left is picked up by the left microphone, and the sound that goes to the right, by the right.
Now imagine that the left microphone is 10cm away from the snare and the right is 3 meters away. How is the sound recorded? Although it is the same sound source the right and left microphones will record the snare hit (the sound pressures in the air to be exact) at different times (see Table 1).
|Microphone Placement Distance||Time for Sound to Travel to Microphone (21°C)|
|10 cm||0.2907 ms|
|3 meters||8.7209 ms|
Table 1: Arrival Times to Microphones
The left microphone will record the initial transient 0.29 milliseconds after the drummer hit the snare and the right mic at 8.72 milliseconds. The stereo waveform would look something like this:
Figure 2: Misplaced Stereo Overhead Microphones
The initial transients of each waveform do not line up with each other. On playback when the left speaker cone is pushing air out towards you, the right is sucking it back - sucks right! Surely we want both monitor cones pushing air out to our ears at the same time, after all, that's how the sound of a real snare arrives at our ears.
“But” .. I hear you say .. “no one in their right mind sets up microphones like that” - one on top of the snare and the other in another part of the room. “Correct”, so let's set them both 1.5 meters apart, or try to! Let's assume that there was a small error setting up the two microphones. The left is precisely 1.5meters away, but the right is off by 1cm (see Table 2).
|Microphone Placement Distance||Time for Sound to Travel to Microphone (21°C)|
|1500 cm||4.36047 ms|
|1501 cm||4.36337 ms|
Table 2: Arrival Times to Microphones
Figure 3: Stereo Overhead Microphone Positions
In Figure 3, the two waveforms are closer together, but they are still not quite right. The left waveform continues to push air out of the left cone while fighting with the right.
While microphone setup and checking phase relationships are essential when recording drums, this is the real world where microphones can get knocked or where you receive tracks from inexperience recording engineers.
So let's retake a look at Figure 3 and think about what we should do to fix this issue. There are two options:
Figure 4: Match the Waveforms
Figure 5: Invert the Phase
Option 1 is possible, and some people manually move one track in millisecond increments to match the other. This can also be achieved with a digital delay. There are specific tools on the market that can also align waveforms. Read the Related Questions at the bottom of this page to see what plugins are available.
Option 2 is the most straightforward - just reach for the Phi (Φ) button! Compared to Option 1, Option 2 is not entirely fixing the problem that the microphone was one centimeter off at setup, but from experience Option 2 is always enough of a fix to get great results.
I bought the waves PhaseIn plugin a few years ago. I played with it for a few weeks when I first got it but haven't touched it since. If plugins lived in the real world, it would have 1cm of dust on the top by now!
Finally, now that we are clear about what the Phi (Φ) button does let's push it! Place an insert on the right track with a phase button, play the stereo overhead tracks and toggle the phase in and out. in some cases you will not notice any discernible difference, but in other cases, the snare will (1) fade out or (2) become more apparent.
If the snare fades out, this means the original left and right tracks can be left alone - switch the phase back off. But if this snare becomes more apparent - sounds better and more upfront - leave the phase switched on, this points to an issue while recording, which you have now rectified.
For the final pieces of the ‘snare-in-phase’ jigsaw, first pan top and bottom snare tracks to the center position then:
Hopefully, your snare sound will now be in good shape so have a quick tidy up and remove any unused phase switching inserts - you don't need those anymore.
You can now go on to check the other drum tracks. Check that the kick-in and kick-out are phase aligned to the overheads, and to each other. Check that each tom is phase aligned to the overhead track.
Finally, decide how wide you want the drums in your mix to be. At the moment they are hard panned left and right, but you can narrow the stereo image to something more suitable to your taste or genre. Turn both pot pans in towards the center by the same amount to tighten the image. I set mine at about 10 and 2 o'clock, but that is a matter of taste.
How do I EQ a snare in mixing? Snare drums come in lots of different shapes and sizes - fat ones, thin ones, steel ones, and wooden ones. They all have different Sonic signatures, but in all cases, their tone can be altered with EQ. Use a healthy 5-7dB boost between 120Hz and 140Hz to add low-end, remove any unwanted ring around 300hz with about 3-4dB gain reduction and add snap by boosting 5dB in the 5-10Khz range.
What phase-correction plugins are available? If the phi button is not enough for your mixing needs, there are a few commercially available plugins to help get those phase issues in check. We have already mentioned The Waves InPhase, but Izotope’s Azimuth, Melda’s MAutoAlign and Sound Radix’s AutoAlign are other great tools. Furthermore, consider using a phase meter like the one on Izotope’s Insight to visualize phase alignment and add an extra level of confidence to your mixing.