Jacquire King - Checking Phase During Tracking

 

 

 

Whenever you record a source with more than one microphone, you risk creating phase problems due to the sound waves reaching the mics at slightly different times. Because virtually all drum recordings utilize multiple mics, it’s critical to be extra careful about the microphones’ phase relationships when setting up for tracking.

In this excerpt from Start to Finish: Jacquire King Episode 2: Dialing In The Drum Sounds, you’ll see Jacquire listening to various drum-mic channels with their polarities normal and flipped to make sure their phase relationships are optimized. The session is for the band Oak and Ash, who will be recording the song, “Keep The Light On.” Before discussing the events in the excerpt, let’s talk a little about drum mic’ing and phase issues.

Phasers on Stun

Not only are there multiple mics in a drum recording, but they are all varying distances from drums and cymbals. That means that each drum or cymbal hit will be captured at a slightly different time through each mic, thus creating phase differences between them. For example, when a drummer hits the snare, its mic is typically right over the edge of the drum’s rim. It will receive the sound waves slightly before an overhead mic, which is further away.

A snare and two overhead tracks zoomed almost to the sample level. The snare hit gets captured about 1ms later on the overhead mics than the snare mic. 

When the drum tracks are combined in the mix, the sound wave from that snare hit will be in a different part of its cycle than the same wave picked up by an overhead mic. That can result in comb filtering, which causes cancellation of certain frequencies, phasey-sounding resonance, thinning out of the overall sound and changes to the stereo image.

You’ll hear an acoustic guitar recorded with two mics about 12 inches apart and 10 inches back from the body in the following example. For the first two measures the polarity of the tracks is unchanged. Then you’ll hear it reversed on one of the channels. Afterward, the stereo image gets a little smaller but sounds more symmetrical, and the tone is fatter.

The badly out-of-phase waveforms from the two spaced-pair mics in the acoustic guitar example. Their peaks and troughs are almost opposite.

The “phase” switch on a console, audio interface, mic preamp, or channel strip plug-in reverses the polarity of a signal, between positive and negative. Reversing the polarity of a signal flips its waveform by 180 degrees. Sometimes by reversing the polarity, it makes the wave cycles line up better and reduces the comb filtering.

That’s what happened in the previous acoustic guitar example. When originally recorded, the two mics’ waveforms were about 180-degrees out of phase with each other. Under different circumstances, reversing polarity could make the phase differences worse. That’s why it’s best to try it both ways. The outcome depends on where the origianl sound waves are in relationship to each other.

Nine on the Kit

In the video, the session is taking place at Flux Studios, and Jacquire is in the control room with engineer Kolton Lee. The band’s drummer, Bryan Garbe, is at the drum kit in the live room.

Jacquire says that they’re revisiting the polarity settings they’d come up with earlier because the snare isn’t sounding quite right in the drum mix.

They start with only the kick and snare channels open, and Bryan playing a simple kick, snare and hi-hat pattern. They compare the sound of the snare with its channel’s polarity normal and reversed. Jacquire observes that reversing the polarity makes the snare sound more focused, with better low-end response.

Next, Jacquire has Kolton open the two channels connected to the outputs of the Royer SF24 stereo ribbon mic, which is being used as an overhead. He asks Bryan to play the kick drum only. They listen to the combination of the overhead mics with the kick and snare mics. Switching the polarity on one of the overhead channels doesn’t affect the sound much.

With Bryan back to playing a kick-snare-hat pattern, they add the mono overhead mic into the mix, but don’t hear any phase issues. Jacquire then asks Kolton to record a few measures with all the mics open.

The waveforms created by recording the drums.

Jacquire is looking at the drum track waveforms at a pretty high zoom level. He is visually checking to see if any of them look like they’re noticeably out of phase. The only one that does is on a track called “Dr. Sample.” The mic is a built-in one on an old Boss hardware sampler of that name. Jacquire put it in the live room to use as a “crush” mic. The SPL of the drums overload it and create a digital saturation effect that can be lightly blended in with the rest of the kit in the mix.

However, if you look closely at all of them, none are lined up exactly. That’s normal and just shows the timing differences of notes recorded by the various kit mics.

Flipping Out 

With Bryan playing again, they try flipping the Dr. Sample channel’s polarity, and it improves the low end and the sound in general. They’re listening with all the drum mics open except the two tom mics and the hi-hat mic.

Lastly, they try flipping the mono room mic’s polarity, and it makes the kit sound fuller. Jacquire explains that due to the room mic’s positioning, the low end sounds better with that channel’s polarity reversed.

Although it’s better to find phase problems prior to tracking, you can address them after the fact in your DAW with an alignment plug-in. Such products offer much more control than you get by flipping the polarity. One example is UAD Little Labs IBP, a plug-in version of the Little Labs IBP hardware unit with additional added features. The plug-in offers a variety of parameters, including timing, polarity and phase.

The UAD Little Labs ibp Workstation Phase Alignment Tool

Besides phase issues caused by multiple mics, sometimes one piece of gear in your signal chain can be wired out of polarity either by mistake or because of differing manufacturer standards. The same can happen from a cable accidentally wired backward. If something you’re recording sounds weird—even if you were only using one mic, try reversing a component’s polarity in the signal chain to see if the sound improves.

DIY

When you’re checking the phase relationships of multiple mics mixed to stereo, it’s always good to listen in mono, where phase problems will be more apparent.

Many EQ and channel strip plug-ins offer a polarity reverse switch like the one above the input fader on Waves Scheps Omni Channel.

For a drum kit with stereo overheads, start your phase check by soloing one of the overhead channels. Flip its phase switch to make sure there isn’t an issue when you hear the pair together.

Next, compare the two overheads with the kick drum mic by flipping the latter’s polarity. If there’s a second kick mic, bring that in next. Then move to the snare, the toms and the room mics. The idea is to find the best combination for the entire kit.

The following audio example includes a drum kit with four mics: kick, snare, and left and right overheads. For the first two measures, the polarities are all set to normal. Then, the left overhead channel’s polarity gets reversed and you hear the stereo image shift and become wider, but uneven. The hi-hat ends up way over to one side.

Here’s the same example in mono, with the polarity switched in the identical spot. Notice how the comb filtering thins out the sound—particularly the snare—after the switch.

After hearing those examples, you probably wouldn’t want to reverse the polarity on that overhead mic channel. But it’s not always cut and dry. In some cases both options sound good and you’d have to make a subjective call.

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