Digital Wireless Latency
glen...@comcast.net
As I begin using digital hybrids to my mixer (delay) and digital
wireless to camera (delay) I realize I am introducing at least one
level of offset - especially if I am recording to my hard drive AND
sending to camera. Not to mention the time differences of hard wired
booms, plants, or the occasions that an analogue wireless must still
come
into the mix.
The 7xx series can record tracks with programable delay; anyone using
this feature with good reason? Or worse, anyone tried to and been
burned?
Glen P.
Scott Farr
I have never had any complaints. I dont use any delay features. The
Lectro 400 series "delay" is un-noticeable
Sergio Sanmiguel
Before I was mixing two 411's + boom & using my 211's as camera hop.
No complaints neither audible problems. Now 'm using a Lectro VRField
which actually takes care of delay matching between analogs & hybrids.
Post doesn't seem to care; but if you do just write it on your sound
report...
~
Serge
glen...@comcast.net
Glen P.
Jeff Wexler
glen...@comcast.net wrote:
> Wow, yet another great venue feature...
>
> Glen P.
Digital latency was a hot topic amongst the users of Zaxcom Digital
wireless when they were first introduced as this was the first time that
most of us were aware of this issue (later, it was something discussed
by Lectro users when Lectro introduced a hybrid wireless that used some
digital technology). After some real world experience with latency, the
general conclusion is that it is basically a non issue (as longs as we
are talking about the 2 to 3 ms delay that both the Zaxcom and Lectro
wireless have). There are issues, mostly issues of mixing style, where
latency is a factor while using both analog (no latency) and digital or
digital hybrid systems (with latency). Again, these issues have been
easily dealt with.
Introducing delay in the recording channel is only useful (and debatably
not necessary) to match systems with latency to systems without.
None of the latency issues have any bearing on SYNC with respect to
picture. The easiest way to understand this is to realize that the 3 ms
delay constitutes approx. 3 feet in distance. Now, think of what happens
in a movie theater where some people are 20 feet from the screen (image
on the screen, speakers behind the screen) and some people in the back
rows may be 60 feet away. Do the people in the back of the theater
notice that the sound is "out of sync"?
A far greater latency problem exists, in your scenario, results from
your sound being recorded in several places and on several different
systems (like your recorder, the camera, etc.). All of these recording
devices have their own specific (and often variable) methods of dealing
with the sound in relation to the picture, and this is the case even if
you were dealing with all analog sources.
Regards, Jeff Wexler
MWeber
area of concern. During a tech specs pre-production meeting last year
the post supervisor commented on numerous phase incompatibilities that
in recent years were becoming more and more of a problem. There have
not been complaints from post regarding digital latency delay because
post has not fully realized what has been causing their problems.
I've found mixing analogue with digital to present situations of phase
shift that made it impossible to blend sources and having either to
mix much more aggressively or totally isolate tracks and let post make
track selections. Keep in mind that a 90 or 270 degree phase shift is
not correctable with a simple 180 degree phase reversal. A corrective
technique that has pulled a smooth mix out of a difficult relationship
is introducing corrective digital delay to the analogue mics. This
delay time usually falls into 3ms for closeup, 4-5ms medium shots,
6-7ms or no delay on wide. Whenever delaying I also note the delay
times on my sound logs.
Since my radio inventory has both analogue and digital units my
original preference for wireless boom was the superior sounding
digitals. This created some problems by the 3ms delay acoustically
moving the boom further (3 feet approx) from the actors. By reversing
my approach and putting digital radios on the actors and analogue on
boom the result is acoustically moving the actors 3ms (3 feet approx)
closer to the boom and the mix is much sweeter.
Last week I had a conversation with Lectrosonics specifically about
the Venue Field system because I heard rumor that it corrected the
latency errors internally. Lectro stated that this was not the case.
Each A/D conversion adds approx 1.5ms latency which they do not
correct for. If I am still mistaken about this please correct me if
I'm wrong.
Mark Weber C.A.S.
Sound Specialist Inc.
Miami, Florida
soundchris
I am using 744 with Lectro 400 radios and Lectro 300 wireless boom for
two years now and never had any problems with "latency". Its easy to
mix and the only problems with phasing occur when two actors turn to
each other and the radios are on similar level. no problems with boom
etc.
btw: if the slate or a plant mic is 10 meters away from the mic the
delay is about 30 ms.
Larry Fisher
We can't remove delay (if so we'd have a time machine and we'd go into
the future to see how it was done) but we can add delay to the analog
channels if you are using a UH200, for instance, with a channel of the
Venue in 200 compatibility mode. This means a UM400 belt pack and
aUH200 boomed on the same performer, could have the same delay through
the Venue mainframe, i.e., would be time aligned.
Best Regards,
Larry Fisher
Lectrosonics
On 25 May 2007 08:30:03 -0700, MWeber <weber...@yahoo.com> wrote:
[snip]
MWeber
Well that is very good news! Last week I recall being told that this
is not what Venue is capable of. Just to be clear, if I run UM400, SM,
and UM200 all receivers on a Venue or Venue Field, then the UM200 will
be time aligned with the 2 other digital transmitters?
If you say "yes" you guys are heroes and have just saved me some
serious dollars!
MW
Sergio Sanmiguel
Yes Mark, They could be heroes indeed...
~
S.
Larry Fisher
Yes. Since this is of concern to you, I am going to spell it out in
more detail than you may need.
A UM400 through any 400 receiver and/or the Venue has a latency of 3.2
ms. A UH200 through an emulated 200 receiver mode on the Venue is
normally half that, or 1.6 ms. The Venue then automagically adds 1.6
ms of delay to the 200 emulation path for a total delay of 3.2 ms so
the UM400 and UH200 are time aligned. (That goes for any model 200 or
400 transmitter of course.) This is not a menu item, it always does
it.
If, due to having this feature, we have indeed assumed heroic
characteristics, I will celebrate by having a nice glass of port
tonight.
Best Regards,
Larry Fisher
Lectrosonics
MWeber
> characteristics, I will celebrate by having a nice glass of port
> tonight.
> Best Regards,
> Larry Fisher
> Lectrosonics
Larry,
By all means enjoy the glass of port. Next week please enjoy my
VRField order!
MW
cmassey
Oh come on Larry, as Billy Sarokin put it, NM is the only place he
knows of where tequila is a food group. No work on Monday, so go for
broke!!!
No salt, touch of lime and a splash of fresh OJ!!!
cleve
Rick PV8945@aol.com
MWeber wrote:
SNIP
Keep in mind that a 90 or 270 degree phase shift is
> not correctable with a simple 180 degree phase reversal. A corrective
> technique that has pulled a smooth mix out of a difficult relationship
> is introducing corrective digital delay to the analogue mics. This
> delay time usually falls into 3ms for closeup, 4-5ms medium shots,
> 6-7ms or no delay on wide. Whenever delaying I also note the delay
> times on my sound logs.
SNIP
> Mark Weber C.A.S.
> Sound Specialist Inc.
> Miami, Florida
Why companies insist on labeling 180 degree polarity reverse switches
as "Phase" is beyond me.They do not affect phase at all. As you have
pointed out, phase is time based, and delaying one track in
relationship to another is the only way to correct this problem.
If needed, I correct both phase and polarity problems in ProTools. I
realize that you are probably mixing in the field without the ability
to line up differences on the fly.
Jeff Wexler
Larry Fisher <lectro...@gmail.com> wrote:
> Hi Mark,
> Yes. Since this is of concern to you, I am going to spell it out in
> more detail than you may need.
>
> A UM400 through any 400 receiver and/or the Venue has a latency of 3.2
> ms. A UH200 through an emulated 200 receiver mode on the Venue is
> normally half that, or 1.6 ms. The Venue then automagically adds 1.6
> ms of delay to the 200 emulation path for a total delay of 3.2 ms so
> the UM400 and UH200 are time aligned. (That goes for any model 200 or
> 400 transmitter of course.) This is not a menu item, it always does
> it.
Thank you Larry for the detailed description of how the Venue system
"time aligns" analog wireless and digital hybrid wireless with latency.
Other posts in this thread seem to indicate to me that there are people
who think (or have actually discovered) that all kinds of nasty phase
issues are going to cause problems in production and in post. One post
actually stated that huge amounts of work are needed in post to "fix"
this problem. What you have stated the Venue system solves in this
regard is also accomplished quite simply by using ALL wireless with
latency or ALL wireless (analog) without; but if these other issues
(which I personally have never encountered), these so-called (mis-named)
"phase" issues, between the boom mic and the lav, etc., ARE issues, then
time aligning isn't really going to solve them.
- Jeff Wexler
Larry Fisher
their lemonade stands.
LarryF
Larry Fisher
I agree that the 3.2 ms probably isn't ever the real issue but in this
limited situation it gets the 3 ms off the table as to whether it is
the problem.
Best,
Larry F
Billy Sarokin
because he was seeing a slight delay (I believe it was arond 20
samples) between my mix tracks and my solo tracks. He wondered what
caused it. The cause was simple. I record up to 10 tracks on my
DVD's. Tracks 1 and 2 are my mix channels, tracks 3 - 10 are each mic
recorded pre-fader. Since the Cameo mixer has only 8 digital outputs,
I send channels 3 - 10 from the Cameo to the Deva via an AES buss
while I send my mix channels via an analog buss. The 20 sample delay
was the additional D/A stage in the analog buss. This delay is about .
5ms, but a talented sound editor could hear the phasing when he mixed
the prefade tracks with my mix tracks. Fortunately, once he knew
where the delay was coming from he could program in compensation into
his system.
It's a constant issue. Every A/D and D/A stage adds delay. Mixing
radios with booms has phasing issues, mixing analog radios with
digital or hybred radios adds delay. Good post mixers can hear it
instantly and shift a track back or forth to eliminate the problem.
Sometimes they miss it and I'll cringe in the theater when a voice
goes hollow or nasel for no good reason. It's not a new issue. It
always existed when mixing any 2 mics together that were not a
coincident pair. It became more apparant when digital processing and
digital recording came into the picture and now it is even more
apparant with the use of digital radios. Post mixers have been
dealing with it for years. Though we can make their lives easier by
letting them know where there are built in and consistent timing
issues in our original recordings (such as the difference between my
mix track and my pre-fade tracks) or the known 2.5 ms delay between
the analog radios and the digital radios.
Billy Sarokin
Sergio Sanmiguel
> A sharp eyed (or rather, eared) sound editor called me a while ago
> because he was seeing a slight delay (I believe it was arond 20
> samples) between my mix tracks and my solo tracks. He wondered what
> caused it. The cause was simple. I record up to 10 tracks on my
> DVD's. Tracks 1 and 2 are my mix channels, tracks 3 - 10 are each mic
> recorded pre-fader. Since the Cameo mixer has only 8 digital outputs,
> I send channels 3 - 10 from the Cameo to the Deva via an AES buss
> while I send my mix channels via an analog buss. The 20 sample delay
> was the additional D/A stage in the analog buss. This delay is about .
> 5ms, but a talented sound editor could hear the phasing when he mixed
> the prefade tracks with my mix tracks. Fortunately, once he knew
> where the delay was coming from he could program in compensation into
> his system.
>
> It's a constant issue. Every A/D and D/A stage adds delay. Mixing
> radios with booms has phasing issues, mixing analog radios with
> instantly and shift a track back or forth to eliminate the problem.
> Sometimes they miss it and I'll cringe in the theater when a voice
> always existed when mixing any 2 mics together that were not a
> digital recording came into the picture and now it is even more
> dealing with it for years. Though we can make their lives easier by
> letting them know where there are built in and consistent timing
> issues in our original recordings (such as the difference between my
> mix track and my pre-fade tracks) or the known 2.5 ms delay between
> the analog radios and the digital radios.
>
> Billy Sarokin
Thanks Billy, that was great...
~
S.
MWeber
> Why companies insist on labeling 180 degree polarity reverse switches
> as "Phase" is beyond me.They do not affect phase at all. As you have
> pointed out, phase is time based, and delaying one track in
> relationship to another is the only way to correct this problem.
Rick,
Your comment is slightly perplexing so I'd like to clarify.
A polarity reverse switch is indeed a proper "phase reversal", (180
degrees) and not time based at all. Positive waveforms becomes
negative and visa-versa. Timing corrections can and will alter a phase
relationship within a very small timing window when similar signals
are mixed but the opportunity for phasing is quickly lost as timing
differences increase and rapidly become time delay effects.
In the field we can have phase cancellations that can be easily
remedied by polarity (phase) switching between certain sources. I for
one always monitor my mix in a mono headphone for just this reason.
The low end is the key indicator of phase incompatabilies before
cancellation occurs. If I can hear it coming before damaging phase
cancellation takes place I can often remove the offending problem
during a live mix with a well timed flip of the "phase reverse switch"
with that channel momentarily potted down to prevent clicks.
Humorously since this is a 50/50 choice as to which source (mic)
requires the polarity switch, this mixer does not always make the best
choice and in a scene with multiple mics I may suddenly complete a
take only to discover I've switched the polarities on maybe 3 of 4
running mics because the offensive mic was the original one left in
normal phase. Same difference - right?
d rosen
larry,
can the 411 emulate (receive clean audio from) an audio 2020?
if so, does it also add the same amount of delay as described for the
200?
many thanks,
dan
Billy Sarokin
> In the field we can have phase cancellations that can be easily
> remedied by polarity (phase) switching between certain sources. I for
> one always monitor my mix in a mono headphone for just this reason.
> The low end is the key indicator of phase incompatabilies before
> cancellation occurs. If I can hear it coming before damaging phase
> cancellation takes place I can often remove the offending problem
> during a live mix with a well timed flip of the "phase reverse switch"
> with that channel momentarily potted down to prevent clicks.
I find the phase reverse switch useable if a mic is known to be 180
degrees out of phase with other mics. I haven't come across it in a
while, but many of my Trams back in the day were reverse phase
(positive pressure on the diaphram would equal negative voltage).
When using those mics I'd use the phase reverse switch on those
channels. There's an easy test. Take 2 wireless mics (do not mix
digital/hybred with analogs since as mentioned they have their own
latency), connect any 2 mics. Hold or tape the mic heads together.
Adjust your trims so both have equal levels. Then open one pot to max
gain and play music or tones so your meters show 0vu. Then open the
2nd pot to max gain. If your meter shows +6 db then your mics are in
phase. If your meter shows a loss of 6 or more db than your mics are
out of phase. Switch any of the phase reverse switches (doesn't
matter which) and your gain should increase to +6. Run this test with
all your mics and you can see which are out of phase with each
other.
Billy Sarokin
MWeber
From: Senator Mike Michaels
To: webersound
Sent: Friday, May 25, 2007 5:38:19 PM
Subject: digital delay in Venue
just a thought, you could also use a 400 series TX in 200 emulation
mode, and add 1.6 ms extra delay to the lav, which is like adding a
foot and a half, and probably closer to the boom mic (at 18")...
Senator Mike Michaels, c.a.s.
Studio M Productions
Sen...@Sound4Film-TV.com
Sound for Film, Video, Radio, TV and PA
Mike,
The availability of any delay has the possibility of being a useful
tool. The hard part is how much and where to put it. The digital
processors in todays HD recorders allow us alot of flexibility to
accurately add delay. Recently I'm carrying an audio analyser on the
cart that among other things, allows me to take FFT instantaneous
delay measurements between sources from which I dial in delay amounts
that are very accurate. This has rendered some very smooth mixing
between mics ie, boom/radios. One still has to be careful for
situations like wide shots where it is the natural delay that makes
these shots sound authentic.
My excitement in the time alignment accuracy of the Lectrosonics Venue
system is that all radio channels now at lease start off lined up and
I can stop the mental gymnastics when considering which wireless
channel to assign based on digital/analogue plus latency delayed or
not.
Thanks for your input.
fatfatjames
How should we mix it? if we mix analog on top of the digital we will
some how have a phasing effect? CAn teach us how to mix in a case of
digital and analog?
On May 25, 9:39 pm, Jeff Wexler <j...@jwsound.net> wrote:
> In article <1180093530.930706.36...@w5g2000hsg.googlegroups.com>,
Billy Sarokin
digital board you can level the playing field by dialing in
corresponding delay to the non digital mics (usually between 2 and 3
ms). If not, it's no big deal. Everytime you mix a body mic with a
boom you are dealing with a similar delay since the boom is often 2-3
feet away from the body mic. Since sound travels approx 1000' per
second, each ms of delay equals approx a foot of distance. If you are
mixing digital and analog body mics you just have to make your mixes a
bit more dramatic by fading out a delay compromised mic a little
faster and a little deeper than normal. The phasing is easy to hear
so as soon as a mic starts to sound a bit 'hollow' get a bit more
aggressive on the faders. I went from using 8 analog radio mics to 6
analog and 2 digital to 6 digital and 2 analog. I have a digital
board so I can program in delay but (especially earlier) I would often
forget. I found the delay issues to be minor and quickly adjusted
for. I believe most people on RAMPS using combinations of digital,
digital hybrid, and analog radios have reported the same thing.
Best,
Billy Sarokin
MWeber
It is not so much a matter of mixing digital with analogue as it is
phase relationships. Anytime you have 2 mics in close proximaty to
one another and as they are mixed together they start sounding thinner
then there is a phase problem. If they are close enough and totally
out of phase then at the point where they are 50/50 mixed together
they will actually cancel each other out and neither mic is heard. We
learn to "mix through" these situations by quickly keeping one mic or
the other dominant so as to prevent cancellation. With dialog between
2 actors you actually rock the mix back and forth between the speaking
actors to prevent thinness and cancellations. As mentioned previously
if the mics are truly out of phase then switching the phase (polarity)
on one of the mic channels brings them back into phase and allows
gentle mixing between the 2 mics without thinning and cancellations.
[To hear pure phase cancellation take any mixer with phase switches,
split any mic into 2 channels of the mixer and put one channel out of
phase. Now mix the channels together and you will hear phase
cancellation at it's finest.]
The problem with the latency is 2 fold. Each 1ms of added delay moves
the acoustic location of the mic approximately 1 foot further away
from the other referenced mic. To picture this, if an actor wears a
bodymic with 3ms latency and a boom mic is right on their forehead
then mixing the 2 mics together will always sound like the actor mic
is approx. 3 feet away from the boom. Secondly, if a phase error is
not exactly 180 degrees out of phase then the phase switch on the
mixer channels will not correct the problem.
[90 degrees out of phase corrected with 180 degree phase (polarity)
reversal either adds (270 degree) or subtracts (-90 degree)]
Delay timing corrections can help us correct these relationships and
keep them more managable.
Larry Fisher
I am sure this is not what you are saying, but the question
(confusion) has come up in several conversations with customers. The
mic with latency still sounds as if it is the actual physical distance
from the actor when heard by itself and that is a different sound than
if it were physically 3 feet farther away. It does have a delay
equivalent to 3 feet of distance but if it were really three feet
farther away it would have a different acoustic blend from the voice,
chest, etc., and more room tone.
Further, the combined sound of a latent lavaliere and a boom mic is
different than either a non latent lavaliere and a boom or a non
latent lavaliere three feet away and a boom mic. I think this is what
you are saying but I can't find a firm definition for "acoustic
location" with Google.
Mark made another important point that this cannot be corrected with a
phase reversal switch.
Best Regards,
Larry Fisher
Lectrosonics
On 30 May 2007 06:23:27 -0700, MWeber <weber...@yahoo.com> wrote:
[snip]
MWeber
to express these points without adding confusion and gave up.
In the actor/boom scenario and as individual mics the latent body pack
indeed does not sound like the mic is 3 feet further away from the
actor and the boom does not sound like it is 3 feet further away from
the actor, however the timing relationship when mixing these mics are
as though the mic'd actor is standing 3 feet further away from the
boom and the delay/phasing can affect the clarity of dialogue.
Yes?
MW
Larry Fisher
LarryF