making -20 read 0 on my super awesome VU's

[Martin]

hi guys,

i know this is likely going to be something to do with weather the outputs are balanced or unbalanced...


when i send a -20 tone out of the fairlight, my meters read 0

when i send a -20 tone out of my magical tone generator, my meters read 0

when i send a -20 tone out of a behr¡nger signal tester, my meters STILL read 0


when i send a -20 tone out of the 002 Rack protools rig, the meters read -7

[chris p]

Martin

There's heaps of info on the existing VU threads, but in short -

(1) its not balanced or unbalanced that's the problem, its different voltage references

(2) 0dbFS (digital ins and outs) is simply an internal reference for the AD DA - its the hottest signal the units can accept or emit. The actual voltage represented by 0db FS varies from equipment to equipment.

(3) 0db on a VU meter is just another voltage. Its up to you where you set it. Typically it is set to somewhere between -16 to -20db FS, but its not set in concrete.

(4) All that your results are showing you is that your 002 has a lower (-7db) voltage output (ie headroom) than the other stuff you mention. The fact that it still calls it "-20db" doesn't mean its the same -20 as any other bit of equipment - see (2) above.

[Martin]

makes sense!

so it just comes down to calibrating the meters to the 002's outs

cause if it says its sending and -20 tone out analog 1 and 2, then it is, i'm just not seeing it properly on the meters

all of what im doing is delivered digitally so i don't need to go back out those outputs, but i would like to see a good representation of whats going on

[rick]

check that tools genetaor is set to peak not rms !

[Martin]

Done that, as soon as the meters only have to play ball with one system i can calibrate it all proper

[vanderlae]

Martin is your VU system off the shelf or built? Interested to know what it is.

cheers

[Martin]

mr vanderlee

its built using rob squire (proharmonic) VU kit, they work brilliantly for the money i think!


the hardest bit is getting my brain around aligning them properly so they swing the same way as the tape house!

[rob]

Chris P's explaination is a good as any.

Levels inside software have a arbitary relationship to analog voltages that go into and come out of converters.

Oh for the days of standards...

but you should be thinking about what 0VU reference you want in relation to FSD and a particular set of converters.

Back in the day when 0VU meant something, then 0VU would be equal to +4dBu.

Reading my article on decibels from Audio Technology iss 57 may or may not help

see here : http://www.proharmonic.com/articles.htm

[rick]

martin if it is any heap the actual digital levels coming out of a protools 002 digital out is correct
i have checked them , but i have never even "heard" the analog output of a 002 rig
anytime i have check has always been with external converters .

what one of my clients does is uses the tools "headphone out " to run the meters only
then he can have a calibrated output level from a 002 set up for tv ( -20 )
make sense ..?

[davek]

Chris P's explaination is a good as any.

Levels inside software have a arbitary relationship to analog voltages that go into and come out of converters.

Oh for the days of standards...

but you should be thinking about what 0VU reference you want in relation to FSD and a particular set of converters.

Back in the day when 0VU meant something, then 0VU would be equal to +4dBu.

Reading my article on decibels from Audio Technology iss 57 may or may not help

see here : http://www.proharmonic.com/articles.htm

From that article..

Two that are widely accepted are –18dBFS = +4dBu and –14dBFS = +4dBu

The 2 standards I am aware of are SMPTE RP155 (where -20dBFS = +4dBu) and EBU R68-2000 (where -14dBFS = +4dBu).

This might be due to my background in broadcasting, but I'm not aware of any standard which places +4dBu at -18dBFS (remembering that the Europeans use an alignment level of 0dBu).

Most of Asia, Oceanea and the USA use the RP155 standard, which has generally been adopted by the majority of broadcast networks in Australia.

I've grown many a grey hair trying to teach trainees the relationship between digital and analogue levels and why it's important to maintain the same amount of headroom for every piece of gear in the signal chain - these kids just don't get it! :)

[ghengis]

Here's a quick great reference - http://hux.com.au/Soapbox%20Items/World ... erence.pdf

Save a copy in your My Docs folder or on your iphone. Explains most of the relationships.

cya
Geoff

[TimS]

Thanks for the artice and link Geoff - top stuff!

[Martin]

aaaand this is why this forum is great.

thanks guys all helping alot!


the headphone out idea may work quite well in this situation too!