Intentional phase cancellation on kick drum

[brandondrury]

I once read an article how Frank Filipetti uses multiple kick drum mics slightly outside the kick (with the head off) to cancel out the 200-500 junk using phase cancellation and no eq. Has anyone tried this? Any tips?

Brandon

[fowler]

Should be easy enough to figure out a good starting distance:

The path length difference between the two mics will cause a comb filter. The basic formula for this is

f = 1/T

where f is the frequency of interest, and T is the time in seconds. Keeping it easy, if not totally accurate, we can say one millisecond equals one foot of distance. That's really about eleven percent less than the "correct" distance but it makes the math easy.

So let's say we have a one foot difference. If you use the "one foot equals one millisecond" (it's a speed of sound thing) then the ".001" is our one foot difference, expressed in seconds (one one thousandth of a second).

f = 1/.001

yields f = 1000 Hz

Now we have our frequency of interest. In the comb filter scenario, a notch occurs at one half t (500 Hz). OK, that's fine, but this is the gift that keeps on giving. You also get deep notches every t Hz, starting with 500 Hz. So you get your big notch at 500, but you also get one at 1500, 2500, 3500, 4500, etc etc etc etc.

Of course much of this will be outside the drum's operating range, so it's a moot point, eventually.

So if you wanted to drop a notch in at, say, 300 Hz, in our equation we want f to equal 600 Hz.

600 = 1/x where x is our desired distance.

x = .0016666666666666 or 1.7 feet. Keep in mind we're saying the speed of sound is 1000 feet per second, not 1134 fps, which makes for stickier math. The one foot = one millisecond is "close" and easy to figure.

So your correct distance is probably around 20 inches. You get your notch at 300 Hz, plus one at 900, 1500, 2100, 2700, 3300, 3900, 4500, 5100, 5700, 6300, 6900, etc.

Aha, but there's more..... :-)

The two sources (microphones) have to be at equal level to do this. Any attenuation to either will cause the notch depths to lessen.

I'll try to post a Smaart transfer function illustrating this. I spend a lot of my time on gigs trying to avoid comb filters :-)

[brandondrury]

Well good god damn!! This is amazing. I sent you 100 marks for posting arguably the most valuable bit of information in the universe.

I've been reading high end forums since 2002 and I've never seen it laid out like that!!!

Amazing.

Thanks a trillion, dude.

Brandon

[DogpitStudios]

Wow,

Just wow.

I think we have a professional on our hands.

Where did you go to school?

Ben

[brandondrury]

Thanks for the compliments, Dogpitstudios, even though I know you weren't talking to me.

ha ha

Brandon

[dach]

Awesomely laid out Fowler...some people also do a lot of math and measuring to place their overheads, etc

I'd like to discuss this a bit more in application with other instruments but just have something else to add that may be helpful... Fowler please add to this or maybe help explain it better.... I'm in a hurry and am just throwing this out there...

Think in terms of a multiple sine waves, one at 100, one at 600 and one at 2.4k
Starting at the same time, at certain points, all these waves will be "in phase" with each other.

When placing your mic at the exact distance from the source where these waves are in phase gives you a more "solid" sound. capisce?

Now let's introduce variables... We now are using an instrument. A clarinet would be the easiest to talk about because of fundamental and harmonic relationship... but lets just say ac gtr playing either a single not or a chord.... Your variables are distance from the source and the individual amplitude of the waves (volume and relationship of the waves to each other)... of course we're not dealing with sine waves anymore... not to mention finding an initial space where the instrument is represented the way you want in the room....

If you find the spot where the instrument sounds best in the room... then sweep your mic up down and all around to find the relationship of lo's/mid's/hi's etc you are looking for that represent the instrument the way you want it... Now fine tune the distance along the same axis the capsule is pointed at the instrument until you reach the point where everything is more "solid", the place where everything is closest to being in phase... there you go.... you can now rotate the capsule axis for "tonal" changes (which is dependent upon the frequency response of the off axis pickup).......

hope that's somewhat understandable...

[brandondrury]

Well noted, dudes.

I'm ready for mic placement theory of this level. Keep em coming.

Brandon

[richiebee]

I don't get this. Why would you do it? Why would you use more resources than you need to? Is it to impress the clientele?

Rich

[brandondrury]

Generally, it's a pretty standard thing to cut a good 12dB @ 300Hz out of the kick drum (give or take). Sometimes, I do much more, but that depends on the drum.

Frank Filipetti http://www.music.com/person/frank_filipetti/1/ mentioned in a recording magazine a few years ago that he has a techique that sounds much better than using EQ. He uses phasing as his EQ on the kick. I'd say it's an extremely advanced technique that wouldn't get used all the time, but it's fun to talk about on a forum.

I've also heard of them doing this on the last "Fuel" record that no one bought, but they used this trick on a guitar cabinet.

Brandon