Checking for phase issues?

I've watched both of Kenny Goia's Tracking Drum Tutes and as long as the peaks and valleys generally line up you are ok. But listen to what sounds best. From what I gather, you can be out of phase by 1 degree or 359. The phase switch flipped changes the phase by 180 degrees. At 90, the phase switch won't help and shifting the tracks to where the peaks align will help that situation. I'm sure someone else here knows more than I do and I will be checking up on this thread.

While you are adding close mikes tracks together you won't encounter many phase issues because the mikes are very close to the source and the next mike near it is much more than three times the distance away.

But with drums say for example it is when you mike the overheads from a little further away you can encounter some issues. Let us suppose you have miked up overheads and close miked all the other drum sounds. If you use mainly the close mikes for the drum sound and just add a hint of the overheads in for some quiet cymbal action then that is the drum sound you will hear and it will be a nice one but a close miked one. (you need more reverbs later though to put this close sound into a room again usually)

Let us say you used two rather larger diaphragm mikes for the OHeads and you want to create most of the drum sound by just using the overheads. And adding in a hint of the close mikes. Now this is a lovely easy way to achieve any decent drum sound. By just using overheads alone. Especially if the drums are nice and tuned and sound killer right there at the time (Sonor like mine!) and the player is consistent with all the surfaces they are hitting. (this is a skill, toms need to be hit harder, cymbals crashed and played way more quiet, hats very light touch too, snare and kick very consistent. Drummers have a lot of problems doing this! People like Steve Gadd are masters at playing every surface perfectly)

You will need to crank up the gain on playback from the overheads then in order to get most of the sound. This drum sound will be pretty stellar except it may be just lacking a little kick detail. So you decide to bring in the close miked kick as well into the picture. The overheads are going to have a lot of kick in them already and now you are bringing in the close mike kick and it is going to mix with the OHead kick either well or not so well. You will never know until you try it.

As soon as you do this the kick sound will either sound even more killer or the kick sound will start to go limp and lack bottom end, a little punch maybe and you will just think not good. This happens because the close kick mike is now adding certain things out of phase compared to the Oheads. But what you can do and I would do this before any time shifting of anything is to reverse the polarity of the close kick sound and what mostly happens is the kick sound now goes from the whimpy limp sound back to a ballsy punchy fat sound again. So you just leave it switch in then. 

If after you insert the polarity reversal plug and the sound gets worse then you leave it off and work with the sound the way it was before. At least you know it was the right way. This also applies to the snare. Snare sound can either stay great or go worse. Then you try the phase reversal thing on the close snare mic.

If you are going to create a drum sound mainly from the O'Head sound be sure to use fat sounding mikes that can go down low. (AKG 414.s U87's etc) No HPF switches in here also. But if you know you are only just going to add a smattering of O'Heads then you can use say AKG 451's with the HPF switched in hard to get rid of a lot of low end in the O'Head sound. When you do this BTW you get less phase issues with the kick because most of the kick sound now is not in the O'Heads any more to react badly with the close miced kick mic

With a guitar cab you might have a close mic and a distant mic. They may or may not add well either and as you start to balance both of them the guitar sound starts to go bad. So try inverting one with respect to the other and often the guitar sound will change back to being more solid again and fat etc..But if the sound really goes bad after inverting one then you have to go back to what you had before and just balance the mikes better.

Phase problems tend to crop up when you are combining more distant mic(s) with closer ones. (on the same source) especially when the distances from the mics to the source are not the same and one is much closer and the other is a distance away. When two or more mics are the same distance from the source you wont have such a phase problem. When a mic is close and the other is distant it is not a bad idea to measure the distance of the distant mic. That way you can calculate the time delay due to speed of sound. You can then try advancing the distant tracks by the same amount of milliseconds and then you can also improve your sound that way too. (1 ms per foot approx or 3ms per yard/metre)

Great stuff Jeff.

Beeps, all the advice you got from everyone is spot on. The only thing I want to add is....when something is phasing, you hear an artifact that makes you go "wtf?!" You won't hear it on a solo'd up track....you'll hear it with the mix of other instruments and you'll just know that something isn't right. It almost sounds like a comb filter of sorts has been applied to an instrument if that makes any sense.

The best way I can explain it is....I have a set of Tascam monitors here. You have to hook the wires up to them in 4 spots. Two silver wires, two copper wires. If I do not put the wires in the right way, it messes with the sound of the monitors putting them out of phase. The sound it makes sort of sounds like one of those plugins by PSP that attempt to put a mono track in stereo. Like...in stereo but not quite. But in the mic realm, it adds this artifact that just sounds weird and filtered. Yet when you solo up the track without the other instruments, you can't hear this artifact.

You just listed another thing I hate about videos and tutorials. Man I so want to release mine. I can't tell you how many times I read something or watch something, where the dude talks about something and doesn't show an example. I just don't get these guys. All this knowledge, yet they keep you in the dark about the things you NEED to learn how to listen for. I've concluded that I am the best teacher in the world. LOL! :) (ok, in MY world that is!)

So if you'renot using a bunch of mic's that may be shooting at each other or creating a delay/distance soundscape, this isn't something you'll need to worry about. However, if a dude is mentioning how he checks for phase in a video, he should at least show what phase is as well as an instance on how he actually corrects it.

For me, I usually use the "fix the mic" technique. LOL! However, this plugin from UAD is simply amazing at fixing stuff like this. I've used it so many times, it's starting to replace "fix the mic" and it truly works!

http://www.uaudio.com/media/assetlibrary/l/l/ll_ibp_hq.jpg

-Danny

Okay... info absorbed.

@Jeff... That was awesome and very concise. Thank you. I guess maybe what was mixing me up was how it was explained to me originally in the context of a snare drum that had both the top and bottom mic's. They mentioned something about how the top mic's diaphragm would be getting pushed inwards while the bottom mic would be pushing outward and then they would reverse as the sound wave went into the opposite direction. That would cancel each other out when the tracks were played together. I indeed had this issue a few times when I was actually micing my drums oh so many years ago. Now I'm realizing that might be only one angle on it or perhaps completely wrong. What I'm getting now from your post is that a phase problem can happen when the waves are slightly out of sync with each other whereas I was thinking it was if they were too perfect in sync with each other. I'm still struggling to wrap my head around the physics involved but at least I'm confident that if I did indeed encounter a phase issue that I could fix it very easily. It was more my hungry mind looking for more munchies. I'm actually trying to get into learning about physics (like all of physics... not just music) so this type of thing is fascinating to me. Anyway thanks again for such a great breakdown and take care. 

@Mike... Thanks but yeah, I knew that much. Independently everything is fine. The sum of the waves is what can makes things wacky. Pretty neat. Kind of like all this stuff about frequencies getting in each others way in a mix and the various ways of handling it. More physics. Cool stuff and I definitely need to dig into it all more. I'm starting to look at music as pure math more than I ever did. 

@Danny... Yes indeed it is infuriating when something gets alluded to then no explanation is offered. I am taking notes on everything as I go along and when this happens it leaves a gap in those notes. You've seen my writing/teaching style first hand and I definitely try to avoid such things. If delving into the topic would derail the current focus I at least make an attempt state as much and then point the reader to an explanation elsewhere. This series I'm currently watching has given me lots of insight but it is very backwards to how I've learned and approached things. I'm not gonna say it's WRONG because I don't know enough to make that assertion but it definitely seems opposite to what I've seen elsewhere. The results seem to be good though and I'm all for different approaches so I'm soldiering on and it'll get put into my notes as an alternate course of action if something I'm doing doesn't seem to be working. There is however a lot of great info on EQ settings, performing certain procedures in Sonar I was not aware of and probably the most beneficial to me is the fact he is using the method of mixing the drums to the overheads and room mics and using the very minimal close mics (just snare and kick) as helper tracks. I've always approached it from the opposite direction (close mics first then overheads for the cymbals). This will be very useful if I end up in a situation where I have minimal mics/channels to work with and I know this is more like how things were done in the past.

Okay... now I'm just blathering but I wanted to come back and thank you guys. Back to the vids. Cheers. 

Beepster
There is however a lot of great info on EQ settings, performing certain procedures in Sonar I was not aware of and probably the most beneficial to me is the fact he is using the method of mixing the drums to the overheads and room mics and using the very minimal close mics (just snare and kick) as helper tracks. I've always approached it from the opposite direction (close mics first then overheads for the cymbals). This will be very useful if I end up in a situation where I have minimal mics/channels to work with and I know this is more like how things were done in the past.

 
The thing to keep in mind with drums is, it depends on your situation. Room mics and all the stuff that goes with them are super important. However, in today's sounds...it's not a common practice for most things. When was the last time you heard a Bonham type drum sound? Or, how about a "strictly room mic" kit or a mid side mic'd kit on a professional mix released to the masses?
 
All that stuff is good to know...it truly is. But you being a rocker/metal head, you're not going to encounter it much because the sounds you need are in your face and direct.close mic'd sounding. See that's the key, all these people brag about these roomy things and mid side mic tecnhiques...don't they realize it sounds like @ss when they compare it to something professionally done? I mean seriously....how can they kid themselves. Yeah, the technique is cool and I like it and have used it....but it sounds like a cheap drum kit in a room because there are no distinct instruments taking over when you compare it to a properly mic'd close kit.
 
Don't get me wrong, I'd prefer less close mic'ing for a live jazz band, live jazz record, live blues band.....but for a rock band, metal band, power pop band, gospal group with power instruments, I'd not waste 5 seconds on a room sound being much of a factor other than adding a slight ambience and stereo spread to the entire kit as an entity very lightly.
 
I work the opposite Beeps. I'll handle the room stuff after I have the drums themselves sounding the way I want. That to me, is the impact. The room, is the ambience and though it needs to be cared for, the dominant instruments in a room are cymbals with the drums that bleed through adding only slightly into the scheme of things. Of course if you kill the room you lose something on the drums, but more room and less drums isn't the answer for impact in MY world. We have such incredible impulses these days and powerful computers, there's just about nothing we can't pull off in a non-destructive world with close mic techniques. But, that's just my thoughts brother. There is no right or wrong....as long as something works for a person, they are right where they need to be.
 
-Danny

Voxengo makes a plugin PHA -979 that does the same thing and runs as VST.

SONAR has a hot key nudge function that can be used as well.



best regards,
mike

Would that be true with a single sound source and two microphones in an anechoic chamber? (allowing for discussion, the fact that a true single point source doesn't really exist outside of theory)



Does that realization describe a circumstance where you have multiple sound sources at different locations?

and/or

Does that realization describe a circumstance where the early reflections are some significant potion of the sound pressure level at at least one of the mics?


Your statement got me to thinking. :-)

I think you are very right Dave. The best anyone can do is to listen while making any sort of adjustments to phase on one of the mics and just go for the sound you want to hear. The fact that phase angles are going to be different for different parts of the spectrum could be used to advantage.

That plugin that Mike refers to is very interesting and you can alter the phase angles of various parts of the spectrum. You could use your ears to get the bottom end of say a kick drum happening. Then turn your attention to the mid range and change the phase angle of the centre part of the spectrum. It could be a good way to alter the sound of the kick before any EQ is applied. An advanced type of tone control.

That approach would work with guitar sounds too using two mics. 

Tweaking phase angles on close mics when distant mics are present is still not the preferred way. I was in a hurry (what happens under severe time pressure and wanted a quick 5 channel drum sound) did an interesting drum recording recently where I use two figure 8 mics to capture 3 toms by putting them in between the toms (one between hi tom and mid tom and the other between mid tom and floor tom) and facing their null points around the snare and kick. They piked up the cymbals nicely as well. Amazingly low snare and kick spill on those tracks resulted. The other three did kick snare and hats. I pulled a great drum sound fast. Being such a lovely player I balanced cymbal and tom levels in my playing. Less time needed later to sort out. The two figure 8 mics panned rather nice too. 

What happens under pressure is you can suddenly devise quick and very time saving ways of doing things eg to capture a good drum sound and spend little time on it later in the mix. It always turns out well usually. There is a situation where you would NOT be spending an hour tweaking the phase angles of mics to get the drum sound right. 

I don't get into too much phasing problems because often I am composing with and work with synths and things and I am dealing a lot with independent samples and outputs etc. And when I do record drums (and anything acoustic)  I often use the approach I mentioned above of recording the bass filtered O'Head sound. (or the complete O'Head sound with all the bass in but not use the close mics much, love that sound too) 

Interesting how under pressure one can alter their approach and get good results in a simpler manner. It is also very interesting to see how your DAW performs under real pressure too especially when the user gets into a serious power usage mode. (eg non stop and fast!) That is another story but I can say Studio One excels in this mode. 

bitflipper


Picture it this way...imagine 2 microphones at different distances from a source. They are positioned such that a 1KHz tone will reach them 180 degrees out of phase. That means 1KHz will be attenuated, along with all of its harmonics; IOW, comb filtering.

Now imagine you move one of the mics such that 1KHz arrives at some other phase angle. Now 1KHz is no longer as attenuated, but maybe now 900Hz is. The comb filtering is still there, but affecting a different series of frequencies.

Reverberation masks this, because copies of the same frequencies will also be arriving as delayed reflections, at different times and different phase relationships. Most will not be comb-filtered to the same extent or manner as the direct sound.

Of course, in an anechoic environment you don't get this masking effect, which is why speakers and microphones and acoustic materials are tested in anechoic chambers. Fortunately, nobody records drums in anechoic rooms (although I'm sure in the 80's they probably would have if it had been an option!)

Hi Bit,


 I was looking at it from a different perspective.


 Let's say you have a sound source in an anechoic chamber and two mics spaced at different distance to the source.


 If you slide the tracks into alignment in post... and it was truly an anechoic chamber... will they not just sync up? That's the question that I was left thinking about when I asked.


 I guess I'm thinking about how your statement suggests, and I agree, that simply sliding 2 tracks, that were recorded in a reflective environment, into alignment will never completely eliminate comb filtering... it will just minimalize the effect.


 I thought it was useful to define a circumstance that is free of comb filtering so that we could discuss where/why/what is getting comb filtered when it does happen.


 If you are sliding tracks into alignment, the comb filtering you can not practically avoid is the extra content coming from reflections and or multiple locations of sound sources. 




 Stuff like that. :-)




best regards,
mike

That's why I keep emphasizing that I am speaking about a circumstance where you have aligned the tracks before you observe how they mix together.

It's also why I mentioned the ideal of a single point source rather than the practical reality of encountering a 113 square inch speaker cone and some cabinet resonance. 

Just thinking out loud.

best regards,
mike

The reason I brought it up is that:

1) It was an idea that flashed through my mind and I was asking for confirmation of the idea... and I'm still open to correction.

2) I suspected that if we agreed that a single or primary source can be aligned than we might be able to agree that the SPL from the reflections etc. may, or may not be, a relatively insignificant portion of the whole. This possible realization might be useful when we consider where and when we find that reflections etc. cause inordinate amounts of undesirable comb filtering.

Consider these examples. If you mic a single 12" speaker guitar cabinet with 1 mic 18" from the cone and a second mic 6 feet from the cone, the results will be very different if the amp is placed out in a sweet spot of a 40' x 70' room than if you have the amp and mic squeezed in to 10' x 11' room.

In other words it's not necessarily the difference in distance between the source and the two mics but rather a difference in distance from the source and the early (please recall that the "early" reflections have the greatest amplitude.) reflections that causes the practical issues.


That's why I am speaking about this... because I think maintaining some context may be helpful to understanding. :-)


As an aside... there are circumstances where you can work out doors and find that the reflections are entirely insignificant... they are simply too low in SPL. Beach sand and an ocean make it all just go away. :-)


best regards,
mike