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mr.incandenza

Super CMIT and wireless phase issues

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Hi everybody, the dialogue editor which is working in a movie I recorded using the Schoeps SCMIT (Output 1, Preset 1 non aggressive one) told me that it's impossible to phase it to wireless mics (Zaxcom + DPA4071). Has anybody else noticed same issues? I'm asking cause I'm trying  to figure out if I got to service it.

Thanx,

Angelo.

 

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The SuperCMIT can theoretically be out of phase with itself, I believe. This would be frequency dependent. The DSP works only up to about 6kHz, so everything below might be a bit delayed. Look at the manual to find out how much (it's not much, but still). To remedy you could try to split off the track at 6k to a new one and attempt to align the two halves independently. It'll be a nuisance at the crossover, though. All this is just a theory of mine. And it'd be crazy if it were true. But theoretically...

Perhaps lav and boom just shouldn't be mixed...

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3 hours ago, mr.incandenza said:

Hi everybody, the dialogue editor which is working in a movie I recorded using the Schoeps SCMIT (Output 1, Preset 1 non aggressive one) told me that it's impossible to phase it to wireless mics (Zaxcom + DPA4071). Has anybody else noticed same issues? I'm asking cause I'm trying  to figure out if I got to service it.

Thanx,

Angelo.

 

You would have phase issues with any boom mic and any wireless in any situation where the mics were moving in relation to each other, right?  Regardless of the electronics involved in mic and wireless, there are time-of-arrival differences that are constantly changing.  If the posties want to mix lav and boom they have to align the two clip by clip. 

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6 hours ago, Constantin said:

The SuperCMIT can theoretically be out of phase with itself, I believe. This would be frequency dependent. The DSP works only up to about 6kHz, so everything below might be a bit delayed. Look at the manual to find out how much (it's not much, but still). To remedy you could try to split off the track at 6k to a new one and attempt to align the two halves independently. It'll be a nuisance at the crossover, though. All this is just a theory of mine. And it'd be crazy if it were true. But theoretically...

Perhaps lav and boom just shouldn't be mixed...

Yeah, It shouldn't but he says he wants to do that in some cases (??) ... He just noticed the other mics work in a different way. I was wondering if I had a problem with this mic.

Thanx.

5 hours ago, Philip Perkins said:

You would have phase issues with any boom mic and any wireless in any situation where the mics were moving in relation to each other, right?  Regardless of the electronics involved in mic and wireless, there are time-of-arrival differences that are constantly changing.  If the posties want to mix lav and boom they have to align the two clip by clip. 

It's exactly what I said him but he says that using other mics this is not happening, maybe he doesn't have clear what is doing :)

thanx

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"Phase" and "Polarity" are often confused. Then throw in latency (system) and time of arrival (through air), and it can be difficult to comprehend.

I'll take a stab at it.

As Philip Perkins mentioned, there is already a time of arrival difference between lav mics and boom mikes of about ~3 to 8 ms, depending on how far the boom mic is from the talent's mouth (sound travels at roughly 1 ft per millisecond). This can not be corrected by inverting polarity on one or the other channels. The only way to correct it (assuming they are mixing the two tracks) is to add delay to one channel to match the later TOA for the other channel.

Then there is the issue of latency which is different for different wireless systems. Analog systems (Sennheiser G2/G3, 2000, 3000 & 5000 Series; Audio LTD 2020/2040; Lectrosonics 190/195/200 Series; etc.) has basically zero latency. Any digital system will have at least 2 ms due to the A/D and D/A process, mostly (plus error correction, other processing, etc.).

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I see that my post (above) has been edited without my knowledge. It is actually factually incorrect now.

We have seen latencies in digital wireless systems as low as 0.9 ms (Quadra IEM system - admittedly not a wireless microphone) and as much as 18 ms. Most are in the 2-4 ms range, which is a tiny fraction of a frame. However, it is still important to note that with some wireless systems, delay may be needed to be added to the wired boom if you are mixing it with a lav and the lav is on a digital wireless system. 

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if you have the super CMIT in ideal position, and a radio mic on the same actor, i do not expect that the two will easily be mixed together. 
you can apply all the latency you like, but because of the nature of the processing of the super CMIT, something will always be a little off.
I say this with no knowledge of the processes in post, but from trying to get this work on set. either use the radios or the super CMIT in the mix but not both at the same time on the same source with a close super CMIT.
 

if you want the boom to mix with the radios in the above situation, then use the unprocessed output and make sure your latencies are all compensated for.

this is the brave new world of digital systems and part of what should be considered in adapting your methods.

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I see that my post (above) has been edited without my knowledge.

What? How did that happen?

That's a bit weird

if you have the super CMIT in ideal position, and a radio mic on the same actor, i do not expect that the two will easily be mixed together. 
you can apply all the latency you like, but because of the nature of the processing of the super CMIT, something will always be a little off.

I agree with this, but have found the same with some other mics, as well.
Besides, I wonder why'd you even want to do that?

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35 minutes ago, chrismedr said:

I guess it was done in good faith to avoid getting this into a zaxcom discussion.
but I agree it feels a bit weird.

My copy-paste  fiasco caused the missing text but it is true that I was attempting to correct some information in 2 of the posts that related to Zaxcom wireless, not to "avoid getting into a zaxcom discussion" but rather to correct some erroneous information and share my own experiences mixing microphones with varying latencies. I have probably had more experience with this than most of the people here on JWSOUND since prior to our use of digital and digital hybrid wireless, latency (the delay produced by digital signal processing) was never anything anyone ever discussed. I have been using digital wireless for 15 years and did have some concerns, based on numbers and specifications, that the latency could pose problems. I remember as well that many people chimed in with speculation and concern that the latency might prove to be fatal to the product (at that time, of course, Zaxcom was the only company shipping a viable wireless mic system for our use). I heard things like "nothing will be in sync", "the boom operator will be confused by the delay and miss the cues", "people in post will have to be shifting and re-aligning the tracks", etc., etc. Well, just about none of this proved to be any problem at all and later when Lectrosonics came out with their digital hybrid (which, of course, has latency) most users also then were able to discover for themselves that the latency introduced by the wireless was essentially a non-issue.

I know that there are people out there that try and use built in delay setting on the inputs of their recorder, but for me personally I have never done this and I have never had any trouble whatsoever mixing a hardwired boom microphone with another microphone going through a wireless with latency. Maybe I have a different mixing style but I never encountered anything that was really any different than all the years and years of mixing all hardwired microphones where the only "delay" issues were physical and positional.

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My copy-paste  fiasco caused the missing text but it is true that I was attempting to correct some information in 2 of the posts that related to Zaxcom wireless, not to "avoid getting into a zaxcom discussion" but rather to correct some erroneous information and share my own experiences mixing microphones with varying latencies.

Well, to be honest, the editing of posts, inadvertently or not, makes me a bit uneasy. It's ok to disagree with someone, but you can state that in a new post.

IIRC Karl's post referred to Zaxcom (and others) only by mentioning actual latency times without any conclusions. Seemed perfectly harmless.

Don't know what the other post was. Anyway, I'd be more comfortable if I knew that no posts get tampered with, inadvertently or not

I have my SuperCMIT on a Zaxcom 742, and the actors on Lectrosonics digital hybrid. The latency between the two systems is around 10ms. This is always audible. Even if I add a bit boom to the Lavs the sound is so weird that it won't sound good. So, either I don't do that, which would make me lose perspective, or I have to delay the lavs by some 10ms maybe even a bit more. Then it can work

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Some months ago I had the opportunity to attend a meeting with Helmut Wittek, talking about Schoeps microphones.

If I remember and understood correctly, he said that the Supercmit processor acts on 4 different frequency ranges, separately. That is the reason (I guess he said) he doesn't recommend it to be combined with wireless mics, because it could have different latency at different frequencies, so it should be difficult to phase it correctly. He told us this mic was not properly intended for our use, but mostly for sports etc.

This is what I think I understood, but if someone can correct me please chime in. 

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51 minutes ago, Constantin said:

Yes, I would dare say it's ideal for us, just care needs to be taken when mixing it with other mics, but that's kind of SOP

I would say it so.

1 hour ago, Jeff Wexler said:

I think Simon Hayes may have something to say about the appropriateness of the Super CMIT for feature films.

I'd love to hear from him about it, there is a german interview on Schoeps site but unfortunately I can't find the english translation.

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On 12/16/2016 at 8:35 AM, karlw said:

"Phase" and "Polarity" are often confused. Then throw in latency (system) and time of arrival (through air), and it can be difficult to comprehend.

I'll take a stab at it.

As Philip Perkins mentioned, there is already a time of arrival difference between lav mics and boom mikes of about ~3 to 8 ms, depending on how far the boom mic is from the talent's mouth (sound travels at roughly 1 ft per millisecond). This can not be corrected by inverting polarity on one or the other channels. The only way to correct it (assuming they are mixing the two tracks) is to add delay to one channel to match the later TOA for the other channel.

Then there is the issue of latency which is different for different wireless systems. Analog systems (Sennheiser G2/G3, 2000, 3000 & 5000 Series; Audio LTD 2020/2040; Lectrosonics 190/195/200 Series; etc.) has basically zero latency. Any digital system will have at least 2 ms due to the A/D and D/A process, mostly (plus error correction, other processing, etc.).

KARL'S MISSING INFORMATION

Lectrosonics Digital Hybrid is about 3 ms, Sennheiser 9000 Series are about 3.4 ms, Zaxcom are about 8 ms.

So, for instance if you had a Zaxcom + DPA4071 like the OP described, on the talent, and a wired (no latency) CMIT on the boom that was 4 ft from the talent, then you would want to ADD about 4 ms to the boom channel to match it with the lav channel.

Karl / Lectrosonics

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Thank you, Mark, for posting the missing info. I do need to make one correction regarding the latency for Zaxcom wireless. There are at least 3 current digital modulations that Zaxcom uses for transmission and each has a different latency spec. The modulation I have been using for the longest time has a latency spec around 3.5ms. I'm pretty sure Karl's suggestions for mixing can only come from an analysis of the numbers, not from actual mixing experience on production. So, as useful as the numbers may be, assuming of course you have numbers, doesn't really tell you how it sounds. As I have mentioned before, we really need to define what we mean by "mixing" when discussing doing a scene while using various sources that have a system latency factor. As Karl points out, any wireless that utilizes digital signal processing will have a latency factor but that doesn't mean you always have to try and match these sources. For me, I have never found it necessary to use any of the available delay on the inputs of most modern recorders and I have done hundreds of scenes mixing sources that are wireless with latency, analog wireless with no latency, hardwired boom microphones, etc. I have mixed entire scenes this way and other than challenging my mixing abilities, these have never posed any technical problems relating to latency, etc. I will add that I still don't fully understand why anyone wants to match (get rid of) the components of delay when mixing a boom mic with a lav. Even in the old days, I remember having a hardwired lav on an actor (I know the idea of having a lav on someone and having to trail a cable seems like ancient history, which it is) and a hardwired boom overhead and mixing these two sources to achieve as certain sound. With hardwired mics, the delay will exist because of the physical distance of each microphone to the source (the voice) and it is this very real world delay that I have used countless times to make the voice sound the way I want it to --- mixing in the boom mic with the lav opens it up and in many cases makes the voice match the picture better, improves intelligibility and restores much of the natural quality of the voice that would be lost by using the lav only. I guess whatI'm saying is that system latency (due to processing times with digital devices) has never been a problem for me and my particular style of mixing and I have been doing this for a very long time. 

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Interesting discussion, with regards to latency being a problem in mixing I'm curious about a situation where the digital latency of the lav exceeds the natural delay of a boom vs lav. If I understand Jeff correctly, in an environment free of "digital latency" the boom signal being delayed against the lav is never a problem in mixing, it can even be beneficial but what if the boom rides the frameline being almost equidistant to the source and the lav has 8ms of latency for example? Can "hearing the boom first" be a problem?

Regarding microphones that have different phase at various frequencies , any of the old 2 capsule systems by AKG (D 224E for example) employed "electro-acoustical"  phase correction at the cross-over point, why would the Schoeps not digitally correct phase across the entire spectrum?

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I pretty much agree, also coming from the "time before digital" and also the time of "wired lavs dragging wires".  The time-of-arrival thing has always been in play when making a mono mix of multiple mics on the same set, whether those mics are booms, lavs on talent or plant mics.  When digital gear came in it was just more of same as far as I'm concerned.  Managing this issue in a mix is part of the art of mixing, in production and in post.  I too have only rarely dialed up delay on mics on location--the situation is too fluid for it to work well, at least for me.

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Thank you, Philip, love the phrase "time before digital", you and I are certainly of the same vintage where we never talked about "the numbers" we just listened very carefully and did our best to make everything sound great.

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Well, even though I am of a time (mostly) during digital, I have still never used delay on set. Except, as mentioned above, with SuperCMIT combined with the Zaxcom 742. the combined delays are too much to go unnoticed. It sound like a slapback echo (with one slap) and once I have dialled the delays in, mixing the various sources of various distances, goes back to how it was before. This is regardless of the trx's modulation, by the way.

There is no point in correcting the delay introduced by the various distances of the mics, as the mics are moving all the time


Regarding microphones that have different phase at various frequencies , any of the old 2 capsule systems by AKG (D 224E for example) employed "electro-acoustical"  phase correction at the cross-over point, why would the Schoeps not digitally correct phase across the entire spectrum?

That's a good question, but I can only assume that they are not doing it, partly by looking at the manual of the SuperCMIT.

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While I often fail to shy away from the nifty mental exercise of theoretical practicality (please note the oxymoron), this discussion seems to fall into the "...Then There's The Real World" category.

Point being, if the goal is to avoid any time domain discrepancies, there's only one way to do it in the real world:  Record the scene with one microphone.  Any use of more than one pickup device where the sound source and the microphones are not each occupying an exact unmovable position, will result in sound pickup of varying delays between the two microphones.

If you don't wish to deal with time domain differences, use one, and only one, microphone.

More than one?  Well... In our profession we should always be "playing it by ear" anyway.

 

 

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The thing I was trying to say, remembering (I hope correctly) the words of Helmut Wittek, is that "the phasing with wireless mics" we're talking about with the SuperCmit is not depending only by the usual factory delays we have with new digital systems, or by the different time the sound arrives to Boom and lavs. 

For what I've understood from his words, you can place a person speaking steady in a point with a lav and a Boom over him (everything locked), and you still will not be able to have the two mics in a correct phase. Even playing with the delay on the channel.

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got word from Helmut directly:

the Super CMIT is perfectly suited for dialog recording in film. However the mic does have different delays for different frequencies that can not compensated for when mixing the SuperCMIT with lavs unless one is using a fir filter, something normally not used by the production sound mixer.

 

 

Screenshot_20161221-083332.jpg

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