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dominiquegreffard

setting delay between boom and lav

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Hi all, Just curious what typical delay do you setup between boom and lav to avoid phasing. My lectro system creates a 3.6 ms so i delay my (cabled) boom channel +3.6ms on my nomad and pretty much leave it at that. What s your recipe do you play alot with it depending of the situation? Cheers!

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What Wyatt say. The problem with phase is not for boom/lav but lav/lav. The Talent 1 lav and Talent 2 lav when the T1 approaching the T2 lav or versa.

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When using a cabled boom mixed with my Zax wireless I usually compare the distance of the lav to the lips with the distance of my boom to the lips. If my Op can get roughly the same distance from the lips as the lav is (in a MED or CU for example) I will delay the boom 3.6ms. This will keep the two sources arriving at roughly the same time. If the boom mic has to stay two feet from the lips (and lav is, say, 1 foot) I'll delay 2.6ms, 3 ft. away and I'll delay 1.6ms, etc..). Of course it is not exact science as the distance can't be held precise but when I don't set any delay with the boom in tight I can hear some definite unpleasant phasing. I just use the math as a rough rule of thumb and listen to the mix to fine tune any delay.

 

In most cases, None! Generally the boom is at such a distance that the laws of physics governing sound speed give you all the delay you would need. (aprox 1ms/ft)

 

If you aren't using digital or hybrid wireless, then no delay is probably your best bet. As the lav is usually a foot or so away from the lips and your boom is usually a foot or foot and half away from the lips.

 

But if using digital/hybrid then no delay would mean your boom would need to be about 4-4.5 ft away from talent in order for two signals to arrive more or less at the same time.

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Lectro digital hybrid is 3.0 ms delay.  Zax digital is 3.6 ms delay.

 

I've never done any delay beyond simply lining up digital vs analog (boom or wireless).  Constantly dialing in delays beyond that seems like a lot of work.

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Never used any delay, never seemed to need it (even if the careful examination of all the specs, distance to the lips, latency in the digital chain, etc., etc. says it's needed). Almost always using Zaxcom wireless on talent and hard wired Schoeps boom mic. 

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I would say that yes, Matt, what you are saying is technically correct...however...In my experience introducing delay to try to phase align mics based on distance and latency is only unnecessarily complicating our work. Phase coherance can be effected by so many other factors like room modes, proximity to hard surfaces, etc. In my experience, these are the things to be avoided or addressed, more-so than latency compensation.

Again, I'm only speaking from my personal experience.

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I too think that setting the delays based on the mics distance is pretty much a futile effort (except perhaps for the delay caused by the digital wireless). It would only work if measured and calculated precisely and if the mics did not move anymore once the delay has been set. And I mean not move even an inch. In a dialogue scene where the boom op is moving between two speakers this is virtually impossible. Also it may confuse post when they are trying to address phase coherence.

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One of the nice features of the Zaxcom Cameo mixer is it's delay screen has the ability to add delay in feet or meters. I use it all the time when I have to walk a wide shot lav into a close boom. Works great.

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I guess I've just adapted to a mixing style that doesn't need to use any delay. All the time I do things like "walk a wide shot lav in to a close boom" and it has never presented any new difficulty once I started using Zaxcom digital wireless. Making a transition from the lav in the wide shot to a boom as they become close enough has always presented some degree of challenge but we all do it, all the time, and either it works or it doesn't. I just don't get the reason for having to use delay.

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Clearly great results can be had either way and it just comes down to personal preference. No right or wrong. It's very interesting hearing everyone's technique.

 

For me, my audio background started in the music industry and I was always taught to be very anal with phase issues any time two mics were recording the same source material if it fell within the 3:1 distance rule. I guess I just carried that anal thinking with me as I transitioned into the location sound world. Perhaps it is not as crucial as I thought it was. Obviously studio recording and live sound mic'ing is much more precise/stable than booming and lavs moving around a set, so I can definitely see the reasoning behind not dealing with it on location.

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post has far more powerful abilities to deal with such things...if they so choose. if you choose to deal with such things on set, get your fingers on your pot that controls ms because you'll have to dial it up or back a ton to keep up with any actor's head movement or boom ops mic movements.

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phase issues any time two mics were recording the same source material if it fell within the 3:1 distance rule.

 

Matt, I may have misunderstood you but the 3:1 rule isn't applicable to mics on the same source.

It's specific purpose is to limit the pickup of say mic B of source A and mic A of source B, and works on the principle that a mic 3x the distance from a source will experience approx. 10dB lower sound pressure than the closer one. This in turn reduces inevitable comb-filtering by limiting the impact of one signal on the other. Basically it is an amplitude tweak rather than time based.

So basically, any two mics on the same source can be at any separation as long as their relative signal levels are at least 10dB apart when ultimately mixed.

Phasey and time-delay issues are another bag and for all practical purposes are as difficult to manage as herding cats.

As an engineer it pains me to agree with the recording bods, but as they say, 'if it sounds good, it is good'.

 

Rob

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Thanks for the input everyone. When I saw this feature in my Nomad I had been wondering how people were calculating it. I imagined mixers computing polynomial differential equations from their carts.

From you all are saying it sounds like it is something only to be used in very trying situations when phasing issues cannot be ignored, and are mixing several different types of inputs without ISOs. Is that sort of correct?

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Making a transition from the lav in the wide shot to a boom as they become close enough has always presented some degree of challenge but we all do it, all the time, and either it works or it doesn't. I just don't get the reason for having to use delay.

+1

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Geez, you guys aren't busy enough mixing that you have to start messing with the delays? That sounds like trying to solve a puzzle that's always changing.  I just work the faders to solve the problem.

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I only use input delays when doing a sitdown interview. I align the boom with the lav. The rest if the time I simply leave my boom input on 3ms ( hardwired compasated for my lectro latency ). But that's more for my own piece of mind more then need.

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I've been in post most of my career.  Trying to dial in a proper delay for same source/multiple mics doesn't work.  In post I would select the best mic and use all others to spot fix problems.  I might move from one mic to another if the scene dictates.  Unless all mics are locked down and your talents heads are locked down, the resulting multiple source comb filter is unusable.  That would be the rule.  Obviously, rules are broken occasionally.

 

The bottom line is adding delays on the set just adds to post problems and complicates your job.

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I've been in post most of my career. Trying to dial in a proper delay for same source/multiple mics doesn't work. In post I would select the best mic and use all others to spot fix problems. I might move from one mic to another if the scene dictates. Unless all mics are locked down and your talents heads are locked down, the resulting multiple source comb filter is unusable. That would be the rule. Obviously, rules are broken occasionally. The bottom line is adding delays on the set just adds to post problems and complicates your job.
Thanks for your input. Good to hear from a post point if view. Just to clarify, in your opinion it is best to allow the 3.6ms latency of digital lavs to go untouched or to add precisely 3.6ms delay to hard wired sources in order to compensate for the latency and in effect have "no delay"? To be clear, with this question I am not talking about compensating for acoustical delay caused by speed of sound/distance but whether or not we should compensate for the latency caused by the digital transmission (since it is a known and constant number).

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"To be clear, with this question I am not talking about compensating for acoustical delay caused by speed of sound/distance but whether or not we should compensate for the latency caused by the digital transmission (since it is a known and constant number)."

 

Although the latency spec is a technically constant number, the existence of a time factor between 2 microphones and how it impacts MIXING is not a constant number (except in the case of a rock solid stationary source and microphones that are not moving at all). This is why I feel it is somewhat pointless (and now we are hearing that it can actually aggravate the situation in post) to dial in any delay when using a microphone on a hard line (with no latency) and a wireless mic (with latency) on the same source. I will add that with ISO recording being the norm these days, if use of delay can solve some problems in post mixing environment then that is where it should be applied. Just my opinion (and this coming from someone who was a very early adopter of these devices where latency was even an issue and there weren't any other devices in production besides the original Deva that could even make use of a delay function).

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"This is why I feel it is somewhat pointless (and now we are hearing that it can actually aggravate the situation in post) to dial in any delay when using a microphone on a hard line (with no latency) and a wireless mic (with latency) on the same source."

 

 

I guess my point is, if I do nothing at all (using no delay to compensate for inherent constant latency in digital lavs) then I am actually delivering tracks WITH a delay and essentially passing on and delivering that delay to post. Whereas if I compensate for the latency then my tracks come out not delayed (in terms of latency) at all and post can then deal with each mics acoustical timing differences (if even necessary).

 

I am not trying to complicate this discussion with semantics, but I am just looking for clarification as to AudioFP's post. I am not sure if he means he would rather get tracks completely untouched (therefore getting sources that could have latency from 0 to 3.6ms) or if he would rather them all be time aligned as if hard wired and then would only have to deal with "acoustic time of arrival differences" if even necessary.

 

To me doing nothing would in essence be "adding delay" but I can't argue with your (and other folk's) results. I think I may be over thinking this subtle issue but nonetheless I am learning a lot from  everyone's varied perspectives.

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You may deliver lav/boom/plant tracks to me but I rarely use more than one source- so "time of arrival differences" aren't a problem.  The .0 to .1 frame latency you mention is insignificant to sync.  On the rare occasions when I have to let more than one track play I will usually align waveforms (using both eyes and ears.)  Even then I might high-pass one and low-pass the other to lessen phasing.  This is all over simplified but I say leave the worry to post.  You operate in real time.  They don't.

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I've been in post most of my career.  Trying to dial in a proper delay for same source/multiple mics doesn't work.  In post I would select the best mic and use all others to spot fix problems.  I might move from one mic to another if the scene dictates.  Unless all mics are locked down and your talents heads are locked down, the resulting multiple source comb filter is unusable.  That would be the rule.  Obviously, rules are broken occasionally.

 

The bottom line is adding delays on the set just adds to post problems and complicates your job.

 

Yup. The only way the delay would become an issue is if you mixed the boom and lav down to mono.

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