Delays in microphone, wireless transmitter, mixer, camera, etc...

[High1ander]

Hi, I just wonder if delay is something that you need to worry about if you have an audio chain that is something like (not specific but just in general)

Microphone -> Wireless Transmitter/receiver -> Mixer -> Camera

How far off could it be in frames? One frame, two frames? Or would it be less than a frame? A frame being in this case a 25th of a second. And do products have any "input output delay" specifications?

I imagine all products more or less have a delay, just trying to figure out how they add up and if one can think "sync sound, is sync sound."

 

[gpforet]

In the particular scenario given, I'd say your latency is going to be less than one frame. This is provided we're talking analog wireless. It really doesn't matter in cases where sound is recorded separately and synced in post since any latency will be prior to the recording and as long as the sticks slapping are lined up with the waveform spike, latency is moot.

You are right, sync is sync. Drift is a different story but far less of a problem with narrative filmmaking than in areas where the takes are 30 minutes long or more. A recent test done with the Tascam DR-680 showed insignificant drift over a 12 minute period.

 

[Richard Crowley]

If you are using analog equipment, generally it is not enough to be concerned about.
If you are using something like a digital wireless microphone, then there is some perceptible delay. Some digital mixers include features to "normalize" the delays between different inputs so that they are all synchronized.
The practical response would depend on exactly what/how you are shooting, etc. You can quite easily "pull-up" the audio/video sync in post-production in any modern editing application. It would not make my top 10 list of things to be concerned about for a production.

 

[davefisk]

The only time I've heard of delay even being a pseudo issue is when using digital wireless like the zaxcom wireless, which had (still have?) a 3 millisecond delay. I personally ran some basic tests, and in the end, it ends up being a non-issue. Lots of people use their digital wireless with no problems. In the analog world, there are no delay issues, even going through an A/D converter if you are recording on a digital recorder or a camera it's a non-issue.

 

[John Willett]

Hi, I just wonder if delay is something that you need to worry about if you have an audio chain that is something like (not specific but just in general)

Microphone -> Wireless Transmitter/receiver -> Mixer -> Camera

How far off could it be in frames? One frame, two frames? Or would it be less than a frame? A frame being in this case a 25th of a second. And do products have any "input output delay" specifications?

I imagine all products more or less have a delay, just trying to figure out how they add up and if one can think "sync sound, is sync sound."

If it's analogue it is, more or less, instantaneous. Speed of light.

Only digital equipment has latency (delay).

The Zaxcom digital radiomic. I have seen does have obvious latency, but how this compares to picture latency I don't know.

If the chain you posted was analogue (eg: G2 or G3 radiomic.) then there would be no latency (delay) at all.

 

[Doc Bernard]

They say it takes 10-20ms before the human mind can notice the difference.

 

[gpforet]

Maybe that's what they say, but I know in my studio, anything more than about 7ms and the artist can feel it. Try it yourself. Put on some headphones, run a signal chain thru a delay and dial-in 7ms and speak into the mic, you'll hear the difference between your head resonance and what your ears are getting. Granted, when watching film synch, since at 24 frames per second each frame is worth approx. 40 ms, I don't think 20ms is going to be a problem in post. Even more to the point, in post you're syncing to picture anyway, so any latency in production is removed during sync.

They say it takes 10-20ms before the human mind can notice the difference.

 

[Noiz2]

Everything has some delay, though as was pointed out analog generally is about the same as a direct wire. Digital does more processing so there is some computational time. That lag varies a lot between devices.

Does it matter? Probably not. Where it's a problem is when your mixing two sends with different delays. But you probably won't be doing that in production. Out of phase sounds are very noticeable at very small differentials. The other case where it could be an issue is with recording music where a slight delay can really throw things off. But again I doubt that will come up in production work.

In your scenario, even if it had a large delay all you would need to do is slip it in post. The DVX100 (original ones, they may have fixed it in the B) for instance has a 1.25 frame delay on the audio out the firewire port. So all footage transfered out of sync. I only met one picture editor that noticed. I would slip the whole OMF when I got it, it bugged me, but I bet most films shot on the DVX100 were not adjusted.

In a large movie theatre there is about three frames of sync shift from the front row to the back row.

 

[Noiz2]

Maybe that's what they say, but I know in my studio, anything more than about 7ms and the artist can feel it. Try it yourself. Put on some headphones, run a signal chain thru a delay and dial-in 7ms and speak into the mic, you'll hear the difference between your head resonance and what your ears are getting. Granted, when watching film synch, since at 24 frames per second each frame is worth approx. 40 ms, I don't think 20ms is going to be a problem in post. Even more to the point, in post you're syncing to picture anyway, so any latency in production is removed during sync.

Phase differences are very perceptible, but I think what he meant was Sync between sound and vision. Up close in the edit room most people can spot 1/4 frame or so. But as I mentioned once your in a movie theatre your much more forgiving.

 

[j1clark@ucsd.edu]

Hi, I just wonder if delay is something that you need to worry about if you have an audio chain that is something like (not specific but just in general)

Microphone -> Wireless Transmitter/receiver -> Mixer -> Camera

How far off could it be in frames? One frame, two frames? Or would it be less than a frame? A frame being in this case a 25th of a second. And do products have any "input output delay" specifications?

I imagine all products more or less have a delay, just trying to figure out how they add up and if one can think "sync sound, is sync sound."

This would only be a significant problem if the feed is live broadcast, and the audio has more delay, and there is no delay line on the video to match up with the late audio.

For material that is destined for editing, any amount of delay, as long as it is constant, can be 'shiffed' out.

 

[Noiz2]

This would only be a significant problem if the feed is live broadcast, and the audio has more delay, and there is no delay line on the video to match up with the late audio.

I was doing one of the Dalai Lama gigs and the video feeding the diamond screen was going through all this high def hardware and it was considerably out of sync with the real world. The producer wanted the place to put in a delay with the sound system so it would sync to the video. He was really adamant till it was pointed out that that would put it out of sync with the real people i.e. His Holiness :~)

 

[Richard Crowley]

The biggest country on the planet is out of sync with the Dali Lama. So what's a few thousand more in the arena?

Delaying speech and feeding it back to the talker is one of the tests for deafness, isn't it? Most hearing people find it difficult to handle without practice.

I was just playing around with a little plastic Sony gadget. It has a little BlueTooth receiver the size of an overgrown ice cube, and that fits into the "hot shoe" of the little handycam. And then a Bluetooth transmitter the size of an overgrown 9V battery (and with a built-in mic) which clips on to the talker. It works pretty good for BlueTooth, but it has a quite noticable latency if you are listening to the receiver with headphones. But digital video recording also has latency (which you don't see while recording) and the final recording has the audio and video reasonably synchronized. The little handycam otherwise has no audio input or OUTPUT connectors.

 

[j1clark@ucsd.edu]

The biggest country on the planet is out of sync with the Dali Lama. So what's a few thousand more in the arena?

Delaying speech and feeding it back to the talker is one of the tests for deafness, isn't it? Most hearing people find it difficult to handle without practice.

I was just playing around with a little plastic Sony gadget. It has a little BlueTooth receiver the size of an overgrown ice cube, and that fits into the "hot shoe" of the little handycam. And then a Bluetooth transmitter the size of an overgrown 9V battery (and with a built-in mic) which clips on to the talker. It works pretty good for BlueTooth, but it has a quite noticable latency if you are listening to the receiver with headphones. But digital video recording also has latency (which you don't see while recording) and the final recording has the audio and video reasonably synchronized. The little handycam otherwise has no audio input or OUTPUT connectors.

Yeah, but this is a problem with 802.11/Bluetooth type deals... I spent my 'late spring vacation' in the middle of nowhere testing video transport via somebody's 802.11 mesh (spell that mess...)... not mine... and constructing a test to find out of the video is even possible to be 'near realtime, with the requirement that there's error correcting... The problem is two fold, one is the viewer of the 'back at the ranch' monitor, needs to know as close to real time as possible what is going on with the remote site...

And of course another requirement is 'no drop outs'... well, without big bux, you don't get that...

There were some ideas about time division multiplexing for 802.11, but almost no one implemented them... while that would not solve every problem it would clean up a number of issues about streaming transports. The error correcting issue is difficult because it may be that the correction info arrives 'too late' and wasting the bandwidth, in addition to adding a delay waiting...

But fortunately for me... the video and audio is interleaved so if one is lost... so is the other...

This sort of thing may gain more presence in the production world, as the use of RF to transport the camera/audio feeds to the 'video village' grows...

 

[Richard Crowley]

Yeah, but this is a problem with 802.11/Bluetooth type deals...

Exactly. I didn't mention it to imply a quality solution, but rather as an anecdote of latency/delay.
The gadget is impressive mainly because it actually works at all (albeit with the latency).

It would be nice if we could use the ubiquitous 802.x data technology for video (or even audio),
but alas, the medium was never designed for that kind of high-bandwidth, real-time application :-(

 

[John Willett]

They say it takes 10-20ms before the human mind can notice the difference.

Maybe that's what they say, but I know in my studio, anything more than about 7ms and the artist can feel it. Try it yourself. Put on some headphones, run a signal chain thru a delay and dial-in 7ms and speak into the mic, you'll hear the difference between your head resonance and what your ears are getting. Granted, when watching film synch, since at 24 frames per second each frame is worth approx. 40 ms, I don't think 20ms is going to be a problem in post. Even more to the point, in post you're syncing to picture anyway, so any latency in production is removed during sync.

20ms is huge and even 7ms is noticeable.

That's why digital radiomics are so few and far between - the technology isn't there yet to get it right.

You really need only 2.5 to 3ms maximum in a radiomic.

But - a digital radiomic. also needs to run for at least 5 hours on one or two standard alkaline AA size batteries and have a frequency response of at least 50Hz to 18kHz. And - it has to fit inside the tight ISO regulation frequency mask.

At the moment it can't be done - and that's why the major manufacturers like Sennheiser and Shure do not have digital radiomics at the moment, even though they have been researching it for at least 10 years - digital is just not as good as analogue.

Those digital radiomics that are around at the moment have had to make compromises of some sort: EG: restricted frequency response, longer latency, special batteries, or pushing the frequency mask to the limits and maybe straying outside (strictly speaking this bit is illegal), or a combination.


PS - Lip sync. in TV vanished years ago. There is hardly any TV program I watch now that is in proper sync. :-(

 

[Richard Crowley]

Lip sync. in TV vanished years ago. There is hardly any TV program I watch now that is in proper sync. :-(

But that is a function of the digital distribution system. The program content delivered to the distributors was in sync.

 

[davefisk]

20ms is huge and even 7ms is noticeable.

That's why digital radiomics are so few and far between - the technology isn't there yet to get it right.

You really need only 2.5 to 3ms maximum in a radiomic.

But - a digital radiomic. also needs to run for at least 5 hours on one or two standard alkaline AA size batteries and have a frequency response of at least 50Hz to 18kHz. And - it has to fit inside the tight ISO regulation frequency mask.

At the moment it can't be done - and that's why the major manufacturers like Sennheiser and Shure do not have digital radiomics at the moment, even though they have been researching it for at least 10 years - digital is just not as good as analogue.

Those digital radiomics that are around at the moment have had to make compromises of some sort: EG: restricted frequency response, longer latency, special batteries, or pushing the frequency mask to the limits and maybe straying outside (strictly speaking this bit is illegal), or a combination.


PS - Lip sync. in TV vanished years ago. There is hardly any TV program I watch now that is in proper sync. :-(

Actually, the Zaxcom wireless systems sound as about as close to a hardline as you can get with very little latency. You should try them out. They are very popular, and do way more than just transmit audio. You should give Zaxcom a call and get some accurate info on them, because part of what you are saying just isn't true, and it's not fair to end users. Lectro has digital hybrid wireless out there, and fully digital wireless as well. I've been down this road because I used to sell ALL wireless systems, and have done shootouts with all of them at the same time, and I've seen all the tests that are run on these things. To say digital can't be done, and isn't as good as analog is a false statement, and I would encourage you to do a little more research on them. I would also encourage end users to look at what the folks over at JWsound are saying about the digital wireless. If digital wireless "can't be done", then why do we see many of the top production sound mixers in the world using digital wireless?

Note: I do not work for, sell, promote, or endorse any particular wireless manufacturer. I am just trying to give accurate information from real hands on experience from myself and other end users who have used most of the wireless systems out there.

 

[Rippie]

Those digital radiomics that are around at the moment have had to make compromises of some sort: EG: restricted frequency response, longer latency, special batteries, or pushing the frequency mask to the limits and maybe straying outside (strictly speaking this bit is illegal), or a combination.

Hmmm Zaxcom has a digital wireless that doesn't have a restricted freq response nor does it take special batteries, nor does it have any noticeable latency, nor is it working illegally.

 

[John Willett]

Actually, the Zaxcom wireless systems sound as about as close to a hardline as you can get with very little latency. You should try them out. They are very popular, and do way more than just transmit audio. You should give Zaxcom a call and get some accurate info on them, because part of what you are saying just isn't true, and it's not fair to end users.

I *have* tried them out and have also looked at the radiation pattern compared to the spectrum mask.

But the Zaxcom to the US spec. is very different to that made to ISO specs.

The US one I saw is illegal in Europe and, from what you say, the very broad transmission spectrum enables them to get a much lower latency.

The ISO spectrum mask used in Europe is very much narrower than the US one and the ones we tried were to this spec. and the latency was noticeable.

I suppose it's unfair to compare a US version to the international version.

 

[Noiz2]

Darn, now that you have pointed this out I'm sure the FCC will sell off some more feq. so we can get up to the European standard... ;~)

I *have* tried them out and have also looked at the radiation pattern compared to the spectrum mask.

But the Zaxcom to the US spec. is very different to that made to ISO specs.

The US one I saw is illegal in Europe and, from what you say, the very broad transmission spectrum enables them to get a much lower latency.

The ISO spectrum mask used in Europe is very much narrower than the US one and the ones we tried were to this spec. and the latency was noticeable.

I suppose it's unfair to compare a US version to the international version.