Drums: O/H Micing technique - Thanks P Casey

[Blast9]

Overhead micing technique mentioned in this thread:

CLA alledged strict hard panned mixing ITB or not?

Originally Posted by P Casey

OK so here it is .

When I used to use DAWs that could zoom to microscopic levels (Radar won't do this) I began to futz with aligning OHs to the snare track (Don't do this, it is overkill and will destroy ambience in your tracks) Anyway I began to wonder how to space my mics on my Ohs so I could always get the peaks and valleys of the waveforms to match each other regardless of distance. That led me to researching the speed of sound. I took that figure and boiled it down to 13.5 inches per millisecond. So when I set my OHs the next time I used multiples of that number and Voila! It worked. As long as you are spacing your mics a whole miilisecond out from your source the source and the microphones will agree in phase. Don't ask me why I don't know why. Anyway I always measure off my Ohs to my snare at multiples of 13.5 and my room mics as well.

Nowadays I only have the phase button on preamps to check my phase but after all these years I still can put the mics in phase with this little formula. BTW I usually use 54 inches out from the snare for OHS. If anyone wants to verify this with their DAW please do!

pat

Thansk Pat -- gonna give this a try

According to an online converter 13.5 inches = 343mm and therefore multiples of 343:

60.5, 121, 343, 686, 1372, 2744 etc which one can therefore apply to room mics thumbsup

[Sean Sullivan]

That makes sense...I think in the Recordman method of OH micing it's recommend the distance is 26 inches...but I guess 27 would be more precise. Go to know and understand.

[username]

Okay, a few things to note..

The Speed of sound is NOT constant, it changes depending on temperature and other factors..

as far as the whole milliseconds thing, theres no scientific reason for that to work.. it could be that you personally don't mind the sound of phasing in those frequency ranges as much, as they'd be octaves of each other (okay, well, sometimes, but harmonics I suppose)

In the live sound world (when doing things like setting up speaker arrays and such) a formula often used to estimate where phase issues are going to occur is 1 foot = 1ms = 1k which depending on temperature is close enough to give you a rough idea.

To get two sources (or in the case of recording receivers) to sum correctly (AND be in time alignment), they need to be within a quarter of a wavelength of each other. So to get two mics to sum coherently up to 1k they need to be within a quarter of a foot of each other, at 2k an eighth of a foot, and so on.

Also, a theoretical total cancellation occurs when two identical sounds are half a wavelength (which can also be expressed as 180 degrees.. but remember this is 180 degrees at a specific wave length.. NOT 180s over the whole spectrum as you'd get with a polarity flip) from each other (this tends not to be total in real life because of a variety of factors, but there should be a large dip there)

Most people tend to suggest avoiding having two mics too close to each other, what your actually doing here is pushing the cancellations down into lower frequencies (and hopefully into the less audible ranges) However, you're also going to start heading into the domain of obvious time related differences.

[wilkinswp]

Humidity will influence the speed of sound. Enough to make a difference in this scenario I'm uncertain. Sound moves much faster through solids and liquids than air. Anyway, I'm always working to get drum mics in phase. However, I don't want to get to the point of sliding tracks around.

[shortyprs]

I'm going back to the old physics classes here, but, unless you're talking close vs. room mics, the speed of sound is not very relevant. With a single mic, what is more important is which frequencies are hitting peak amplitudes at the distance between the mic and the source. For example, 54 inches is about 1/4 of the wavelength at 61.74hz. If there are more than one mic one a source, the issue is whether the waves enhance or cancel out each other. So, mic's spaced 54' and 13' 8" from a snare will be at opposite peak amplitudes at 61.74hz and cancel each other out.

Short of maybe 15 feet, you aren't hearing any difference because of the speed of sound. You're just hearing which frequencies are hitting their peak energies at that distance. At least, that's what I remember from physics class. If this is wrong, could somebody explain why?

[username]

Your almost right..

The distance of a wave length is directly proportional to the speed of sound

[shortyprs]

The difference in wavelength based upon the maximum range of the speed of sound in your recording space is thousandths of a millimeter. It isn't even close to physically possible to hear that kind of difference in wavelength (from a stationary source....we're not talking doppler effect here). In addition, the wavelength of a 40 foot wave isn't somehow suddenly dramatically shortened just because you put your ear at 54 inches. Putting your mic at 10 inches vs. 100 inches will not change the wavelengths of sound. It only changes what part of the wave is picked up. So far, I'm still not finding the physics to back this theory up.

Speed of sound issues come up when:

1. the difference in the speed of electricity generates wave forms that are out of phase with the speed of sound;

2. Multiple mics are not the same distance from the source (how close or how far apart determines which frequencies are likely to be out of phase....which is why the IBP let's you adjust phase in either high or low frequency content);

3. Mics are far enough away from the source that they pic up either direct source waves or sound reflections that are either out of time with the music or out of phase (in the case of reflected waves).

The bottom line is, set the first overhead where it sounds good (emphasizes the right frequencies). Set the rest of the overheads or room mics where they do the least damage to the beautiful tone you found in the first mic.

But, if you can change conditions in your studio enough to significantly alter wavelengths, you need to stop it.....cause everyone in the room just died.

[iflyinmymind]

This is all facinating, but i do remember reading that 'pat' said it worked for him.. even if its not supposed to work..

[username]

Originally Posted by shortyprs

The difference in wavelength based upon the maximum range of the speed of sound in your recording space is thousandths of a millimeter. It isn't even close to physically possible to hear that kind of difference in wavelength (from a stationary source....we're not talking doppler effect here). In addition, the wavelength of a 40 foot wave isn't somehow suddenly dramatically shortened just because you put your ear at 54 inches. Putting your mic at 10 inches vs. 100 inches will not change the wavelengths of sound. It only changes what part of the wave is picked up. So far, I'm still not finding the physics to back this theory up.

Speed of sound issues come up when:

1. the difference in the speed of electricity generates wave forms that are out of phase with the speed of sound;

2. Multiple mics are not the same distance from the source (how close or how far apart determines which frequencies are likely to be out of phase....which is why the IBP let's you adjust phase in either high or low frequency content);

3. Mics are far enough away from the source that they pic up either direct source waves or sound reflections that are either out of time with the music or out of phase (in the case of reflected waves).

The bottom line is, set the first overhead where it sounds good (emphasizes the right frequencies). Set the rest of the overheads or room mics where they do the least damage to the beautiful tone you found in the first mic.

But, if you can change conditions in your studio enough to significantly alter wavelengths, you need to stop it.....cause everyone in the room just died.

Okay, several things,

Your right in saying the changes in temperature arent a huge issue, especially as they effect all mics in the room equally.

Having just re-read your post and my post I think you might have misunderstood what was I was trying to say. I was purely talking about cancellation effects when using two sources.

My only reason for bringing up the the speed of sound was to point out that not only was the whole milliseconds theory a bit strange, but that it would actually have had a slightly different effect depending on temperature.

The OP talked about the mics "agreeing in phase" with each other. What I was trying to get at was that the close mics are overheads won't be free of phase interactions simply because they're whole millimeters away. They may sound great like this, it may even move the phase interactions to frequency ranges that are less obvious, but it won't leave the mics in phase with each other.


If you want to start getting heavily into getting better phase alignment on drums, I'd suggest buying yourself smart live and a decent measurement mic and doing some proper measurements.

[sluttygearhere]

Maybe it's just me. But I don't understand why there has to be a science behind it. .. I just put my mics up and move them around until they sound wonderful to me. What wrong with doing it by guy and feel?

[username]

Nothing wrong with doing it that way at all!..

However I've personally found that having a bit of technical understanding of whats going on has allowed me to speed up the process if finding good sounds. And also given me some ideas of things to try that I probably would have never had otherwise..

To me it's the same as music theory vs writing by ear and such. Both ways work best for different people and theres people on both sides who'll tell you that the other way is completely wrong.

Hope I haven't offended anyone, as this was definitely not my intent!

[sluttygearhere]

I don't think you have offended anyone. I didn't mean to come off as saying that anyone was wrong for doing it the scientific way. I love the science and the physics behind sound and recording and engineering. but I tend to be a little more free when it comes to micing things up and getting the sounds I want. I have known people that would just do it the technical/scientific way even if it didn't sound as good as it could have. As far as I am concerned if it's 100 percent correct by the science and it still sounds wrong its wrong. I am all about learning more of the physics behind it. but when it sounds right it sounds right. and that's usually where I stop. Sorry if I came off kinda bashing the ideas and stuff. didn't mean to at all.

[shortyprs]

Yeah, username, I think we're both saying the same thing about waveforms and phase issues and we both have issues with the speed of sound theory. You are dead right saying a bit of technical understanding speeds things up.

Bottom line, if it sounds good, it is good.