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Old 22nd November 2003, 12:32 AM   #1
EC8010 is offline EC8010  United Kingdom
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Default Is absolute phase nonsense?

Recording a snare drum, there's such a difference in timbre between the sound outside the skin and within the drum that it is conventional to place two microphones, one either side of the skin, and adjust relative levels to produce the required sound.

To avoid bass cancellation, one microphone must have its polarity inverted. Which one? And why?

This is not intended to be a trick question. If we can't answer this question, then absolute phase has to be questioned as being an anomaly in the replay system. Perhaps air linearity in small boxes...
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Old 22nd November 2003, 12:44 AM   #2
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Hi,

Quote:
To avoid bass cancellation, one microphone must have its polarity inverted. Which one? And why?
The microphone in front of the drumskin because the impact's is higher on the rear of the skin and it's therefore more realistically being picked up by the mike on the other end.

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Old 22nd November 2003, 12:54 AM   #3
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I'd be prepared to put money [well, a fiver (5), anyway] on most recording engineers inverting the inside microphone. Which, in a way, proves my point. You have presented a logical argument, yet I'm fairly sure it's ignored.

[edit] The distance the skin moves is the same, whichever side we observe...
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Old 22nd November 2003, 12:57 AM   #4
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Wouldn't this also depend on the frequency of the drum's tuning, the corresponding wavelength and the distance to the skin of both mics?

:)ensen.
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Old 22nd November 2003, 01:02 AM   #5
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Hi,

Quote:
I'd be prepared to put money [well, a fiver (5), anyway] on most recording engineers inverting the inside microphone. Which, in a way, proves my point. You have presented a logical argument, yet I'm fairly sure it's ignored.
Yes, that's what I expect most of them to do anyways...

Regarding the main topic though, no, I don't think absolute phase is nonsense at all.

Guess you noticed I'm a Blumlein fan?

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Old 22nd November 2003, 01:04 AM   #6
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Hi,

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Wouldn't this also depend on the frequency of the drum's tuning, the corresponding wavelength and the distance to the skin of both mics?
Nope.

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Old 22nd November 2003, 01:09 AM   #7
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First, I think this is a wrong forum or at least wrong area of the forum ( Tubes?) to ask this question.
Second, there is no single correct answer to the problem.
As a recording engineer who used this technique a lot I can tell you that every snare drum responds a bit different to this way of miking. Depending on the depth of the drum itself, relative and absolute tuning of both heads and playing technique of the drummer the results of flipping the polarity of the bottom mic can be perceived as an improvement, change for worse, or just a change without a clear favorite. Also, changing the relative level of the bottom mic will sometimes change the prefered polarity setting.
The textbook/recording school method is to match both mics in level and the polarity that results in fuller sound is the correct one. Then adjust the bottom mic's level to taste. The problem is that sometimes it is impossible to tell which setting is fuller. They both sound bad or good or just different. Also, remember that 99% of the time snare mic is just one of many picking up snare's sound. Highly compressed overhead mics and room mics can carry more information about the snare in the final mix than the dedicated snare mic(s). If you consider that those can be delayed anywhere from 5-15 msec. (due to sound propagation delay) in relation to the close mic, the comb filtering effect can be greater than anything resulting from interaction of the top and bottom mic on the snare drum.
As to absolute polarity with regard to snare drum, on an isolated sample it could be audible, but the distinction could be easilly lost depending on positioning of the close mic.
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Old 22nd November 2003, 01:16 AM   #8
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Default Blumlein rules OK! Yet...

But most recordings are multi-miked, so...

Does anyone have any idea of the proportion of genuine Blumlein recordings using a pair of "figure of eight" crossed microphones that have been made, compared to the multi-miked stuff?

The Decca "tree" technique definitely didn't meet the Blumlein criterion, but it produced some cracking recordings.
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Old 22nd November 2003, 01:19 AM   #9
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Hi,

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Second, there is no single correct answer to the problem.
Not to my mind but it seems a lot of sound engineers are already participating in the production process even before they're asked to.

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Old 22nd November 2003, 01:24 AM   #10
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Blumlein technique is used a lot of times in addition to the standard multimiking. I have seen guys replacing spaced overheads with an M-S setup and keeping all the close mics. It works well for room miking of choirs because it reduces the amount of comb filtering present in spaced omni's.
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