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Calibration help Virtual Instrument Plugins
Old 28th January 2006
  #1
Lives for gear
 
John The Cut's Avatar
 

Calibration help

Hi, I'm basically trying to calibrate all my gear properly but getting hopelessly confused with dbU, dbFS and the way the gear handles things.

Here is the chain -

Cubase SX > Rosetta 200 > Soundtracs Topaz > Speakers

Ok, I have setup MDA TestTone and PSP Vintage Meter in Cubase. TestTone is running a 1kHz sinewave at 0dB, TestTone also set to 0dB = 0dbFS.

PSP Vinatge Meter set to VU shows this tone to be 0dB... is that 0dBU on a VU meter?? Cubase channel and master faders show -12db (dbFS?)

I have reset the Rosetta200, and this tone appears to be -16dbFS. The Master VU meters on the Topaz I have set to 0dB (dbU?) using the gain pots with the channel faders at 0. (there are no calibration levels on the Topaz Gain pots!)

So I have many questions. Does the Rosetta need to be calibrated to show this level as -12dbFS? If -12dbFS = 0dbU then my VU meters are going to be hopelessy pinned whenever I am mixing, since then I push 0dbFS...

Can someone, anyone help me makes sense of all this level stuff? Where does +4dbU fit into this equation. Just trying to learn something..
Old 28th January 2006
  #2
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John The Cut's Avatar
 

bump
Old 29th January 2006
  #3
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hociman's Avatar
 

decibels

Quote:
Originally Posted by mogWai
Ok, I have setup MDA TestTone and PSP Vintage Meter in Cubase.
I am vaguely familiar with the PSP Vintage Meter, but what is MDA TestTone ?
Quote:
Originally Posted by mogWai
TestTone is running a 1kHz sinewave at 0dB, TestTone also set to 0dB = 0dbFS.
Ok, here is an opportunity to clarify this dB business. dB is an abbreviation for decibels. Decibels are a logarithmic measurement, which means they are not a linear measurement. 1+1=2, but 1dB+1dB != (the "!=" means does not equal) 2dB. Decibel measurements are always referenced to a nominal operating level, which is defined as 0 dB. Not only are decibel measurements referenced to a nominal operating level, but they are also referenced to another measurement! To truly understand a measurement expressed in dB, you need to know...

1. The measurement that is being referenced to.
2. What the 0dB value of the referenced measurement is.

Read on and I will address these points.

Quote:
Originally Posted by mogWai
PSP Vinatge Meter set to VU shows this tone to be 0dB... is that 0dBU on a VU meter??
This is most likely 0dB VU. dBu (yes, capitalization matters) is a measurement referenced to voltage. If a measurement is expressed in dBu, then it is referenced to 0dBu, which is defined as 0.775 VRMS (voltage measured using root mean square). The u in dBu means unloaded (high-impedance circuitry sees low impedances connected to them as negligible, which is essentially unloaded - no load connected). I will not go into RMS measurements, as that would sidetrack us from your initial goal (though you should strive to understand that concept too).
Quote:
Originally Posted by mogWai
Cubase channel and master faders show -12db (dbFS?)
You would have to RTFM for Cubase to know for certain what ballistics those meters use. If they use the same ballistics as other channel meters in other DAWs that I have used, then yes, the scale would be dBFS. To tie dBFS into the lesson, a measurement expressed in dBFS is referenced to Full Scale digital, with 0dBFS being the greatest signal value that can be represented in the digital realm.

Quote:
Originally Posted by mogWai
I have reset the Rosetta200, and this tone appears to be -16dbFS.
The Rosetta 200 ships with its calibration set to -16dBFS according to TFM.
Quote:
Originally Posted by mogWai
The Master VU meters on the Topaz I have set to 0dB (dbU?) using the gain pots with the channel faders at 0. (there are no calibration levels on the Topaz Gain pots!)
Forgive my ignorance, but I do not know what a Soundtracs Topaz is. However, I can still help you. Again, just like the PSP meter, this is most likely 0dB VU. Since there are no markings for the trims on your Soundtracs Topaz, it is wise to have the faders at 0dB (unity gain) for this process.

Quote:
Originally Posted by mogWai
So I have many questions.
I hope I have many answers.
Quote:
Originally Posted by mogWai
Does the Rosetta need to be calibrated to show this level as -12dbFS?
Yes. This results in your signal chain having unity gain. At the moment, you are losing 4dBFS between Cubase and your Rosetta. Think of it as having a fader between Cubase and the Rosetta. If you did, in your current setup, said fader would be -4dB below unity (0dB). Since the goal of calibration is to have every device operating with unity gain, you need to calibrate your Rosetta. The procedure is in TFM.
Quote:
Originally Posted by mogWai
If -12dbFS = 0dbU then my VU meters are going to be hopelessy pinned whenever I am mixing, since then I push 0dbFS...
That problem is outside the scope of simple calibration. If the VU meters will be hopelessly pinned (which damages them, by the way), then either change your mixing style or don't bother using them.

Quote:
Originally Posted by mogWai
Can someone, anyone help me makes sense of all this level stuff?
I hope I just did.
Quote:
Originally Posted by mogWai
Where does +4dbU fit into this equation.
+4dBu (remember, capitalization matters) means that a device is operating at 4dB above (hence the + sign) 0dBu, which was defined above as being 0.775VRMS. The u was defined as meaning the high impedance circuit has no load connected. So if 0dBu = 0.775 VRMS, then what voltage is represented by +4dBu? This is where the log and anti-log keys on your calculator become useful. The formula for calculating voltages with logs is dBu = 20 log (base 10) Vo/Vi where dBu is the reference value, Vo is the output voltage, and Vi is the input voltage. We know that 0 dBu = 0.775VRMS, so to determine what voltage corresponds to +4dBu, we calculate it as

4 = 20 log (base 10) Vo/Vi
4÷20 = log (base 10) Vo/Vi
.2 = 10 log (base 10) Vo/Vi

Now we take the anti-log of .2 This can be thought of as raising 10 to the power of .2.

10 anti-log .2 = Vo/Vi
1.585 = Vo/Vi

Now, we know the input voltage is 0.775VRMS, so

1.585 = Vo/0.775
1.585*0.775 = Vo
1.228VRMS = Vo

We have just calculated that audio equipment whose nominal operating level is specified as +4dBu operates at a nominal voltage of 1.228VRMS! stike What are the implications of this? Well, besides learning some math, you now know that if your audio interface outputs, Rosetta I/O, and Topaz inputs are all specified to operate at a nominal level of +4dBu that you could use a voltmeter at each point in the chain to verify that everything is operating at unity gain by checking to see that the voltage is 1.228VRMS.

Quote:
Originally Posted by mogWai
Just trying to learn something..
I hope you did. This was a nice refresher course for me as well.
Old 29th January 2006
  #4
Lives for gear
 
No4PCs's Avatar
Hi friend

Quote:
Originally Posted by hociman
I am vaguely familiar with the PSP Vintage Meter, but what is MDA TestTone ?

Ok, here is an opportunity to clarify this dB business. dB is an abbreviation for decibels. Decibels are a logarithmic measurement, which means they are not a linear measurement. 1+1=2, but 1dB+1dB != (the "!=" means does not equal) 2dB. Decibel measurements are always referenced to a nominal operating level, which is defined as 0 dB. Not only are decibel measurements referenced to a nominal operating level, but they are also referenced to another measurement! To truly understand a measurement expressed in dB, you need to know...

1. The measurement that is being referenced to.
2. What the 0dB value of the referenced measurement is.

Read on and I will address these points.


This is most likely 0dB VU. dBu (yes, capitalization matters) is a measurement referenced to voltage. If a measurement is expressed in dBu, then it is referenced to 0dBu, which is defined as 0.775 VRMS (voltage measured using root mean square). The u in dBu means unloaded (high-impedance circuitry sees low impedances connected to them as negligible, which is essentially unloaded - no load connected). I will not go into RMS measurements, as that would sidetrack us from your initial goal (though you should strive to understand that concept too).

You would have to RTFM for Cubase to know for certain what ballistics those meters use. If they use the same ballistics as other channel meters in other DAWs that I have used, then yes, the scale would be dBFS. To tie dBFS into the lesson, a measurement expressed in dBFS is referenced to Full Scale digital, with 0dBFS being the greatest signal value that can be represented in the digital realm.


The Rosetta 200 ships with its calibration set to -16dBFS according to TFM.

Forgive my ignorance, but I do not know what a Soundtracs Topaz is. However, I can still help you. Again, just like the PSP meter, this is most likely 0dB VU. Since there are no markings for the trims on your Soundtracs Topaz, it is wise to have the faders at 0dB (unity gain) for this process.


I hope I have many answers.

Yes. This results in your signal chain having unity gain. At the moment, you are losing 4dBFS between Cubase and your Rosetta. Think of it as having a fader between Cubase and the Rosetta. If you did, in your current setup, said fader would be -4dB below unity (0dB). Since the goal of calibration is to have every device operating with unity gain, you need to calibrate your Rosetta. The procedure is in TFM.

That problem is outside the scope of simple calibration. If the VU meters will be hopelessly pinned (which damages them, by the way), then either change your mixing style or don't bother using them.


I hope I just did.

+4dBu (remember, capitalization matters) means that a device is operating at 4dB above (hence the + sign) 0dBu, which was defined above as being 0.775VRMS. The u was defined as meaning the high impedance circuit has no load connected. So if 0dBu = 0.775 VRMS, then what voltage is represented by +4dBu? This is where the log and anti-log keys on your calculator become useful. The formula for calculating voltages with logs is dBu = 20 log (base 10) Vo/Vi where dBu is the reference value, Vo is the output voltage, and Vi is the input voltage. We know that 0 dBu = 0.775VRMS, so to determine what voltage corresponds to +4dBu, we calculate it as

4 = 20 log (base 10) Vo/Vi
4÷20 = log (base 10) Vo/Vi
.2 = 10 log (base 10) Vo/Vi

Now we take the anti-log of .2 This can be thought of as raising 10 to the power of .2.

10 anti-log .2 = Vo/Vi
1.585 = Vo/Vi

Now, we know the input voltage is 0.775VRMS, so

1.585 = Vo/0.775
1.585*0.775 = Vo
1.228VRMS = Vo

We have just calculated that audio equipment whose nominal operating level is specified as +4dBu operates at a nominal voltage of 1.228VRMS! stike What are the implications of this? Well, besides learning some math, you now know that if your audio interface outputs, Rosetta I/O, and Topaz inputs are all specified to operate at a nominal level of +4dBu that you could use a voltmeter at each point in the chain to verify that everything is operating at unity gain by checking to see that the voltage is 1.228VRMS.


I hope you did. This was a nice refresher course for me as well.

Hi friend, are you a scientist? Very good information, but all we need make this "adjuments" in our computer set up?
Old 29th January 2006
  #5
Lives for gear
 
hociman's Avatar
 

breakdown

Quote:
Originally Posted by No4PCs
Hi friend, are you a scientist?
No, just someone who is expected to know most everything (even though that is not humanly possible ).
Quote:
Originally Posted by No4PCs
Very good information, but all we need make this "adjuments" in our computer set up?
Hmm, well I supposed I thought wrongly that the theory could be applied by the user. Someone would read it and have an epiphany and say Oh, ok! This is what I need to do. Perhaps I was wrong.

1. Play a 1kHz sine tone whose dbFS level you want to represent 0 dB VU. Make certain that all of your faders in your DAW are at unity (0 dB gain) with no other processing.
2. In mogWai's case, he wants to calibrate his Rosetta 200. So he routes the sine tone output of his DAW into his Rosetta. He then calibrates the Rosetta 200 so that its meters indicate the same level as his sine tone is set to in his DAW.
3. Again, specific to mogWai, he sets the faders on his Topaz at unity (0 dB gain) and adjusts the trim until the Topaz meters indicate the same level as his sine tone is set to in his DAW.
4. If he wants to be certain he is operating at unity gain throughout the above chain, he can use a voltmeter to measure his DAW's output and his Rosetta's output to be 1.228VRMS.

I hope that breaks it down better for you.
Old 27th July 2009
  #6
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junior's Avatar
 

Was just searching the boards and came across this thread from a few years ago. Thanks for the well thought out post, hociman. Very nice explanation!
Old 27th July 2009
  #7
Gear Maniac
 
The True Buck's Avatar
 

Damn junior, I was just calibrating my rosetta and went here to ask some questions and you just brought this back to life... Thanks alot!
Old 28th July 2009
  #8
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junior's Avatar
 

Perfect timing, I guess...
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