Lavalier Phase Calculation

[HarrisKarlin]

Hi All,


I don't think this question is idiotic, but pardon me if I'm about to make an ass of myself.


I tend to ignore it on location if a lav is out of phase with boom, aside from a note in my reports. It's such a quick fix at the editing level, I'd rather just get both sources running sweet.

However, it occurred to me today that I have no clue how to factor in the 3:1 rule for that. How do you make that adjustment when the first mic is essentially 0 inches from the sound source?

This isn't really relevant in day to day, but I'm curious if someone else figured this out.

[Wayne]

Originally Posted by HarrisKarlin

.. It's such a quick fix at the editing level, I'd rather just get both sources running sweet.

However, it occurred to me today that I have no clue how to factor in the 3:1 rule for that. How do you make that adjustment when the first mic is essentially 0 inches from the sound source? ..

..when the first mic is essentially 0 inches from the sound source..Yes that is the good question when this comes up. thumbsup
It would seem that you are presuming 3:1 is a phase aligment method?

It is not. It is for attenuating (by distance) the unwanted delayed cross bleed pick-up between two mics on two different sources.

Put another way, to achieve the same effect in a 'one source' near-far micing -you would just turn the far mic down so as not to hear the phase/delay mess. (I doubt that's your intent.

[HarrisKarlin]

Not by my understanding.


3:1 is the rough rule to get two mics in phase relative to distance from source. If they're attenuating delays, it's because they're in phase with one another.

[Wayne]

Originally Posted by HarrisKarlin

Not by my understanding.


3:1 is the rough rule to get two mics in phase relative to distance from source. If they're attenuating delays, it's because they're in phase with one another.

Yes, there is a lot of that around.

'Zero is the only place in time where mutiple frequencies (anything but a single simple frequency) can be in phase.
That's not to say a given out-of-phase combo can't sound good..

[Yannick]

3:1 rule has nothing to do with phase relationship, as the 3:1 rule doesn't even know which frequencies are involved ...

The 3:1 rule can even become 2:1 rule when using highly directional mics, or as said above, when the levels will not be equal.

It is all about the comb filtering that will exist when mixing both signals, without time aligning, and at equal levels.

The 3:1 rule then says that the result will not be too dramatic, that's all.

Of course, this rule does not incorporate more complicated matters, as eg. the phase relationship between the opening of a piano and above the lid, or the phase relationship between the top and bottom soundboard of a violin.

etc etc

In short, time aligning in this instance will only help if you hold the subjects head in a vise screw !

[Wayne]

One of the menbers made a spread sheet a while back that shows how frequencies come in and out of alignment at various distances..
(damned if I can find now though..

[pkautzsch]

Originally Posted by HarrisKarlin

Not by my understanding.


3:1 is the rough rule to get two mics in phase relative to distance from source. If they're attenuating delays, it's because they're in phase with one another.

3:1 "rule" is about the far mic picking up the source ~10 dB softer than the closer mic, as then the sound through the far mic will be sufficiently masked by the sound through the closer mic. This applies to omnis, or both mics pointing the same way. Pointing cardioids at different sources can easily make it a 2:1 or even 1.5:1 relationship, depending on the second mic's angle to the first source (and vice versa).

[just.sounds]

Maybe try to delay it more than it should. if it is speach you could get away with probably 10ms delay without it being echoey. And 10 ms should get you pretty much out of the comb filtering zone. Because it is probably a lot of trouble to mess with a variable delay to keep them perfectly alligned.

[Wayne]

Originally Posted by just.sounds

Maybe try to delay it more than it should. if it is speach you could get away with probably 10ms delay without it being echoey. And 10 ms should get you pretty much out of the comb filtering zone. Because it is probably a lot of trouble to mess with a variable delay to keep them perfectly alligned.

Originally Posted by HarrisKarlin

Hi All..
...I tend to ignore it on location if a lav is out of phase with boom, aside from a note in my reports. It's such a quick fix at the editing level, I'd rather just get both sources running sweet.

However, it occurred to me today that I have no clue how to factor in the 3:1 rule for that. How do you make that adjustment when the first mic is essentially 0 inches from the sound source?

This isn't really relevant in day to day, but I'm curious if someone else figured this out.

If I read it right, he was sliding post. The question was '3:1 to fix phase'.