How to calibrate VU meter using trim ?

[Rokus666]

I just got PRO VLA II
the front panel has a trim function on the VU meter. Does anyone know how to calibrate meter accurately?
It seems when I load the input, VU is barely jumping, and in my daw it reaches "0"db

[Pascal Sijen]

Originally Posted by Rokus666

I just got PRO VLA II
the front panel has a trim function on the VU meter. Does anyone know how to calibrate meter accurately?
It seems when I load the input, VU is barely jumping, and in my daw it reaches "0"db

You can use the -20dBFS 1Khz test file from our website. You will need a true RMS volt meter and then calibrate the signal path so that the output of your D to A = 0dB VU (typically 0dB VU is equal to +4dBu / 185 nanoWebers per meter / 1.23 Volts RMS - using a true RMS volt meter). This assumes a balanced signal path.

Download the test files by following this link.

I hope this helps.

Cheers!

[Rokus666]

I don't have RMS volt meter unfortunately.
I have radio shack SPL meter and Fluke 73 III multimeter.
I am not sure if any of those can read RMS
is there any other way of doing this ?

[Pascal Sijen]

Originally Posted by Rokus666

I don't have RMS volt meter unfortunately.
I have radio shack SPL meter and Fluke 73 III multimeter.
I am not sure if any of those can read RMS
is there any other way of doing this ?

Unfortunately your Fluke is not very accurate at that frequency, within in that voltage measurement range (rated to 500Hz). If you can find a 100Hz @ -20dBFS test file, then it should work (your multimeter isn't true RMS, but because the stimulus is a sine wave, it should be OK). Just connect pins 2 and 3 from the XLR to + and - respectively.


Cheers!

[Rokus666]

I am going to try to do this right now.
I am not even sure how to use meter. I was thinking just to shoot the -20 dbfs trough the channel of the device. Should that be 0 dbVU on the device ?

[Pascal Sijen]

Originally Posted by Rokus666

I am going to try to do this right now.
I am not even sure how to use meter. I was thinking just to shoot the -20 dbfs trough the channel of the device. Should that be 0 dbVU on the device ?

Yes.

Typically -20dBFS is equal to 0dB VU (0dB VU is equal to +4dBu / 185 nanoWebers per meter / 1.23 Volts RMS)

Good luck!

[Rokus666]

I am a little bit confused.

I took the signal generator from my DAW,1khz sine wave,
Put the signal to -20db, panned it hard left, and the VU input section of the device is reading -7 db VU (all controls normalised)
I can't even trim the meter to come to 0 db VU
The meter can go small increments up and down.
Am I doing something wrong ?

DAW(cubase internal signal generator) 1khz sine -20 db panned left going to input of the compressor with normalised settings. The readout is somewhere around -7 and the meter lets me tweak it maximum +-1 db
So I am not sure if I left out any of the steps...

[Pascal Sijen]

Originally Posted by Rokus666

I am a little bit confused.

I took the signal generator from my DAW,1khz sine wave,
Put the signal to -20db, panned it hard left, and the VU input section of the device is reading -7 db VU (all controls normalised)
I can't even trim the meter to come to 0 db VU
The meter can go small increments up and down.
Am I doing something wrong ?

DAW(cubase internal signal generator) 1khz sine -20 db panned left going to input of the compressor with normalised settings. The readout is somewhere around -7 and the meter lets me tweak it maximum +-1 db
So I am not sure if I left out any of the steps...

It sounds like something in the chain is not operating at +4dBu. Without being able to measure the electrical levels, or knowing what gear is in the chain and its nominal output level, it will be hard to tell what is going on. It sounds like you are running things nearer -10dBv into a meter looking for +4dBu (−10 dBV is equal to 0.3162 volts or −7.78 dBu, as apposed to +4dBu / 1.78dBV).

Cheers!

[Rokus666]

I am 100 % sure that the metering on the compressor device is depressed to +4

My sound interface line out should automatically be at +4

I am going TRS out of MOTU828 to XLR into the compressor unit.
The VU on the device is reading around -7 (this is monitoring on the input meter of the compressor unit)

I am pretty sure MOTU doesn't have -10 +4 switch (it's automatically +4)

http://namm.harmony-central.com/WNAM.../828-large.jpg

[Pascal Sijen]

Originally Posted by Rokus666

I am 100 % sure that the metering on the compressor device is depressed to +4

My sound interface line out should automatically be at +4

I am going TRS out of MOTU828 to XLR into the compressor unit.
The VU on the device is reading around -7 (this is monitoring on the input meter of the compressor unit)

I am pretty sure MOTU doesn't have -10 +4 switch (it's automatically +4)

http://namm.harmony-central.com/WNAM.../828-large.jpg

Maybe someone with more knowledge of your gear can shed some additional insight. However, without being able to measure the RMS level of the test signal coming out of your MOTU and going into your meter, it would be hard tell where the issue is. Maybe contact MOTU and see if they have any thoughts.

Cheers!

[Rokus666]

One weird thing is that when I pressed the switch on the compressor to -10


Now i get:

-20 db 1khz sine wave going to compressor at -10 metering pressed on.

In input mode, VU Reads less than 1 db VU
In output mode, VU reads 0 (only with threshold set to 0)

Well, for now the meters are symmetrically calibrated until i figure this confusion out.
Thank you for the help and getting you involved in all this mess.
ART manual doesn't say anything about calibrating the unit, so I am emailing people in ART and see what they are going to tell me.

[Mgr]

Hi I am in the same process actually will follow this thread to see what you guys find out. Also have a question : i have read some info and they were telling to callibrate at -18dbfs to 0 , do you know anything about the difference between -20dbfs.

thanks

[Rokus666]

I have no clue really.

I am not even sure if -20 db is coming out of MOTU 828 at +4 or -10 and I don't really have a way of measuring it. The manual says it's +4 (inputs and outputs) But the device meter is totally acting weird.
Input, output and bypass give me different combinations of a meter readouts, all different levels on the VU. So I am kind of lost, don't even know which stage to take as a reference. Input, output or bypass ?
I have the old mBox, probably I can use line out of that and use pro tools signal generator. I don't even know if mbox is +4 as well.

I have sent ART an email 2-3 days ago and still haven't got the reply.
I am totally new to trimming the meter on PRO VLA II and hope to get some clarification on levels and metering.

[DanH]

Not to resurrect this thread from the grave as I'm sure you've found the answer elsewhere. There is no true level conversion standard between the analog and digital world. There are several guidelines that people have adopted.. -18dBFS, -12dBFS, etc. But the only way to truly know that your converters are putting out +4dBu (1.23 RMS volts) is to use a meter. My rig at work, for example, requires -12dBFS.