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Audio specification

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Baz Leffler
Audio specification
on May 30, 2009 at 5:05:55 am

Forgive me if I seem to be asking a silly question here but most of the 'experts' I talk to regarding this matter seem to have different opinions.
When I make audio mixes for broadcast I use Steinberg's Nuendo (better than protools) and have Motu digital interfaces. I have AES out of the Motu going into a very accurate AES digital VU. In Nuendo I set my 1Khz tone (reference) to -20 on Nuendo's VU and it shows exactly -20 on the separate outboard VU. When I connect this same AES output into a Digibetacam it also shows it as exactly -20. So I can safely assume the signal path is correct.
So when I do my mixes and being a little old fashion I have large outboard analog VU's set to show ZERO VU using -20 tone as reference. Then when doing my mix I never allow the signal to exceed 0 VU.
But when I play my mix and look at the accurate digital VU's it shows the loudest parts at -10 with the occasional -9 and a rare -5 but none of this shows on the analog VU's. I know there is a difference in metering ballistics between the two types but this difference is of concern.
Firstly, if a constant signal such as 1Khz tone shows as -20 on a digital VU and 0 on an analog VU why does my mix never exceed 0 on the analog VU but goes up to -10 (and increase of 10) on the digital VU? (Analog tone = 0 program = 0, Digital tone = -20 program = -10).
Secondly, the spec for my programs is nothing to exceed -10 but just using my analog VU's I would have assumed that nothing was exceeding -20 given the fact that I set 0VU to equal -20 tone and no program content went over 0VU!!!
Thirdly, I send a program to say, Discovery Channel and it passes their QC but I send the same program to a local network and they reject it because the audio levels exceeded -10 on the odd occassion. I have always regarded Discovery Channel as the tightest spec ever and have never had a reject.
Of course in the olden days we never had digital VU's and we mastered using analog VU's and never had a problem but I am not sure what to believe.
Does the occasional foray into the -10 to -5 range constitute an 'out of spec' mix or is that to be expected? I find it almost impossible to reign in the odd door slam or sudden thump no matter what compressor settings I use.
But in the end I know there is no digital clipping or any such detriment to the final product but a spec is a spec. Can anyone here shed some light or lead me to where I can read up on such things?

Baz

What would I do without the 'UNDO' button!!!!


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maurice jansen
Re: Audio specification
on May 30, 2009 at 11:46:46 am

well Baz

i guess you call all your meter's VU
but that's not what they are. all though i don't know your setup.
i have the strong feel that the external analog meter you talk about is a Real VU meter with the ballistic's required for VU-measurement.
the meter's in your Software and on the Deck are PPM-meter's
A PPM (PeakPulseMeter) is designed to reveal te peak levels in a signal
even for short transient's
a VU(Volume Unit) is designed to give a indication of the loudness of a program. In broadcast the meter to use is a PPM for Analog and Digital.
if you look to the ballistic of a PPM you will see that it react's very fast and will go down real slow giving you the time to see the Max levels on your channel. in the digital domain the Integration time is about as short as 1uS and the release about 1,5S.

in Europe we use for broadcast/analog signals DINScaled PPMmeter's where 0dB = +6dBu integration 10Ms Release 2S
in Europe for lineup
when going from Analog to Digital
-9dBm(on the PPM)=-18dBFS(DIGI/SoftWare)=-3dBVU(your Analogmeter)=-3dBU
in US (as far as i know not sure though)
0dBm(on the PPM)=-20dBFS(onDIGI/Software)=+6dBVU(yourAnalogmeter)=+6DBU

through the difference in ballistic's this is only true with a Lineup tone there is no good correlation when used on dynamic material.
using VUfor broadcast is not the way to go the meters on the DIGI
are indicational not full spec. i guess you have to use your
softwaremeters or buy a External PPM (my choice)

please anyone give comment on the USlevels ?!?!

greet
Maurice




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Bob Zelin
Re: Audio specification
on May 30, 2009 at 11:34:19 pm

Maurice gives an excellent description. Your digital meters are called peak meters. Different analog meters respond differently. For dramatic example, the Sony UVW-1800 has "LED" meters (not a VU meter with a needle), but shows the average signal, not the peak signal. So you set for zero tone on a UVW-1800, and then playback your program material, and everything looks low ! But it's not.

Every station has a different delivery specification. Stations like Discovery Channel have a new audio delivery spec, that required the use of the $3000 Dolby LM100 meter, to insure that you are delivering your audio program level at -23dB full scale. Without this expensive meter, it's pretty difficult to pass their delivery spec. For local stations, I have never had a tape rejected as long as the damn tone level showed up at zero - because this is how most of these numskulls set level anyway. Analog 0VU, or digital -20dB
corresponds to +4dBu in the United States. So zero on a Mackie 1604 mixer, zero on a Sony UVW-1800, or -20dB on a Sony DVW-A500 are all the same - +4dBu.

You will never get away from the ever changing delivery specs of a TV station.

Bob Zelin




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maurice jansen
Re: Audio specification
on May 31, 2009 at 7:35:14 am

ok baz

forget what iwrote about the US levels
and replace it with
-20dBFS(onDIGI/Software)=0dBVU(yourAnalogmeter)=+4DBU
if you still have to deliver on SP
don't forget that the crazy people of sony have put different meters in every differnt betaSPmodel (hate this).
BVW = PPM (in my opinon the only good SP serie they made)
PVW = VU
UVW = crapy (VU)

greet
Maurice





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Baz Leffler
Re: Audio specification
on Jun 1, 2009 at 12:08:58 am

Thanks guys - All this info is valuable and seems to be where I am at but it still doesn't explain how a VU can't see 10db of variations that the PPM meter see's.

Another 'baffler' is the built in tone generators of my Digibeta and HDCAM decks are set to -20 but I am constantly told my tone should be set at -18. Shouldn't someone tell Sony? (please don't tell me there is a menu item for that...)

Someone once told me that video was the most complicated part of television production but I now know that not to be true. While the 'video' has the color, 'audio' has the "gray area".

Baz

What would I do without the 'UNDO' button!!!!


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Bob Zelin
Re: Audio specification
on Jun 1, 2009 at 2:02:31 am

you write -
Thanks guys - All this info is valuable and seems to be where I am at but it still doesn't explain how a VU can't see 10db of variations that the PPM meter see's.

reply - you STILL have not told us exactly what piece of equipment you are refering to. I thought that both of us gave excellent detailed examples. The VU meter CANNOT RESPOND fast enough - this is why tone looks correct, and average audio level does not. The UVW-1800 meters are NOT ACCURATE. This means, (to use Maurice's wonderful example) a Sony BVW-75 Beta VTR, a Sony PVW-2800 Beta VTR and a Sony UVW-1800 Beta VTR, the UVW-1800 meters would "look" WRONG with the same audio going into all three VTR's. Does this confuse you, or do you understand and accept this. If you would simply say EXACTLY what kind of equipment you are refering to (where is your VU meter), then I can address this -


you write -
Another 'baffler' is the built in tone generators of my Digibeta and HDCAM decks are set to -20 but I am constantly told my tone should be set at -18. Shouldn't someone tell Sony? (please don't tell me there is a menu item for that...)

REPLY - exactly WHO is telling you that your tone should be set to -18 ? The industry standard (which is based on Sony's popularity) is -20dB full scale. When all of this first started to happen, Panasonic was making a DAT machine called the SV3700 (I think that was the model # - it was a long time ago). And all the audio guys used it in NY, and they wanted everyone to standardize to -18. But Sony Broadcast could not give a CRAP about Panasonic, and everyone would say "do I set for -18 or -20 ?". What they all didn't get was that a +4dBm (now dBu these days) signal would show up as 0 VU on analog VTR's, -20dB on Sony VTR's, and -18 on Panasonic DAT machines, so it was all the same. You DONT uncalibrate a Sony VTR to match a Panasonic standard. At that time, AVID was popular, and the default setting on AVID's (that used Digidesign Audio Interface boxes) was -14. this REALLY caused confusion at the time. In the next generation of AVID, AVID allowed you to change the reference level, so it could show up at -20, instead of -14, and then everyone was happy. DAT started to fade, and everyone forgot about -18.
So ONCE AGAIN - WHO is telling you that you should be setting up to --18 ?

And just to confuse you, when ANY station has a delivery requirement (like Discovery Channel) for -23dBFS, do you know what you do - you just shut up, and follow their requirements.



you write -
Someone once told me that video was the most complicated part of television production but I now know that not to be true. While the 'video' has the color, 'audio' has the "gray area".

REPLY - what are you talking about. Video is more confusing than ever now - WAY more confusing than audio. You have a MILLION HD standards, and now countless frame rates, and compresion formats, and file formats. Video has become insanely confusing because of this. (Do you want your HD image to be 720p, 1080i, 1080p, 23.98, 24, 29.97, 59.94, and do you want it DVCProHD, ProRes422HQ, DNxHD, etc, etc, etc.). If all we had to worry about was analog audio level, life would be easy. Besides, almost everyone has switched to SDI embedded audio anyway (which doesn't get rid of the level issues, but analog audio is all but dead now anyway).

Bob Zelin





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Baz Leffler
Re: Audio specification
on Jun 1, 2009 at 3:23:49 am

[Bob Zelin] "you STILL have not told us exactly what piece of equipment you are refering to"

Sorry I thought I did mention "Steinberg's Nuendo", "Motu digital interfaces", "Analog VU", "AES digital VU", "Digibetacam" and later I mentioned "HDCAM". Do you need me to mention the brand names/model numbers? Incidently my audio post suite uses a totally digital path which includes SDI, AES and TDIF.

[Bob Zelin] "I thought that both of us gave excellent detailed examples."

Yes you both did and I do believe I thanked you for it.

[Bob Zelin] "The UVW-1800 meters are NOT ACCURATE"

I do not have a UVW-1800 so that is no concern to me.

[Bob Zelin] "Does this confuse you, or do you understand and accept this."

Yes I understand and that is why when refering to the digibeta and HDCAM decks I always use the audio level meters set to MAX where the scale becomes +/- 2dB.

[Bob Zelin] "If you would simply say EXACTLY what kind of equipment you are refering to (where is your VU meter)"

My audio post suite has Multiple PPM and VU meters - my audio program (Nuendo) has PPM, I have a digital audio desk with analog group outs feeding large Tascam analog VU's and also feeding AES (digital) PPM VU's. The audio desk itself has digital meters (useless for accutate reading) as do my Tascam DA98 decks.

[Bob Zelin] "exactly WHO is telling you that your tone should be set to -18"

This from my deliverables contract -
"AUDIO LEVELS:
If the audio levels for the master tapes are measured in the analogue domain then the audio reference level for all the four Channels must be -11 dB. The Maximum overall programme peak level is 0 db full scale.
If the audio levels for the master tapes are measured in the digital domain then the audio reference level for all the four Channels must be -18 dB. "


[Bob Zelin] "Panasonic was making a DAT machine called the SV3700"

I have a SV3800 in my audio suite so I am very familiar with the machine. I do not use its metering for anything accurate.

[Bob Zelin] "what are you talking about. Video is more confusing than ever now"

Once a specification for video is required in the deliverables contract it is locked in but not necessarily so for audio - thus my 'gray area' comment.
But I did fail to mention the fact for video the max white is 100% and should never be exceeded in a master tape otherwise the 'gamut' monster will come and get you. But most camera's tend to set their clippers to about 105% and this has been the case way back to the old analog days but that is for another discussion.

Baz

What would I do without the 'UNDO' button!!!!


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maurice jansen
Re: Audio specification
on Jun 1, 2009 at 8:51:58 am

Hi Baz/Bob

all our Digidecks have there reference tone to -18dBFS
i guess it's part of the EBU audio package which also make's
that -18dB on the deck is -9dB on the analog output.
which is different than the US standart
it's how you buy it. another trick is to give Embedded audio on the input
and let bars and tone come out of your NLE.
i can have a look if these settings are in the hidden maintanace menu
of the deck but i don't have this manual at home.
and this is also the menu where things can go really wrong.

greet
Maurice


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Baz Leffler
Re: Audio specification
on Jun 2, 2009 at 12:13:04 am

[maurice jansen] "all our Digidecks have there reference tone to -18dBFS
i guess it's part of the EBU audio package"


Interesting... I am using PAL decks here in Australia which I thought would have come under the 'EBU' banner..... I shall do some more research...

Baz

What would I do without the 'UNDO' button!!!!


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maurice jansen
Re: Audio specification
on Jun 3, 2009 at 9:57:16 pm

Although australia is big

you may contact a sister company of the company i work for
called Prestiegne Charter i'm sure they can help you out.
knowing all about your local specifications.

Unit 1/59 Jersey Road
Bayswater, Victoria
Australia 3153

Tel: +613 9729 0222
Fax: +613 9729 4400

greet
Maurice


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maurice jansen
Re: Audio specification
on Jun 15, 2009 at 4:49:15 pm

Hi Baz

maybe a bit late but i found out where you can adjust the headroom of your meters in a DVW500.
this is done in a hidden menu.
first
==> NEVER EVER <==
Do things in this menu if you don't know what it is. adjusment can look if they did not do anything but you can endup with tape's that can only be playedback in your deck. due to differences in RFlevels on the tape.

if your lucky you can enter this menu with the frontpanel.
when your in the standard menu keep CTLpressed and momentary press SET.

if the menu does not change you need to open the deck and change
BIT7 on Dipswitch S100 on the SSboard. the longboard nearest to the drum on the right when the frontpanel face you.(wow hope you find it)
this gives you access to the special menu.

when your in the special menu you can navigate with the menu button the set button. changing things goes the same way as in the normal menu.

go to menu C4
and then to C47 here you will find your meter setup.

succes
Maurice



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