+3 Tape Calibration Question.

[Brian Roth]

I think not because the approximate difference between 185 and 355 is 7 or even 8dB and the standard reference is 320 at 0Vu (+4dBu).

I disagree. Look at that chart posted in #11 above. Difference between 185 and 355 is 6 dB.

320 is a useful reference level most commonly used in Europe and discussed in the "Choosing and Using" document from MRL.

Bri

 

[Brian Roth]

So to go back to the original questions " I have a 355nWb MRL. I need to calibrate for +3 on a 320nWb reel (ATR Master)" If you want +3 over 320 using a 355 test tape you need to set the playback metering to -1Vu. On a side note, this is pretty damn hot!

That seems correct to me using the chart from post #11. And indeed plenty hot!

Bri

 

[GabrieleP]

This is a picture I just took of an old gadget from Quantegy.
355 as fluxivity is an odd number but I guess it could be translated as 370.
"Step #1: Determine operating level and reference tape fluxivity".
If they match you must read 0 dB on the VU meters.
If the required operating level is higher than the fluxivity specified on your alignment tape, you must read values lower than 0 dB on the VU meters.
If the required operating level is lower than the fluxivity specified, you must read values higher than 0 dB on the meters.
Your client requested +3 but did not specify over which reference fluxivity... did he?
If it is +3/185 and your alignment tape is 370, then your meters should show +3 dB VU.
It it really is +3 over 320, that translates to a +8 over 185: your alignment tape should read -1 db on the VU meter!
Then again: will the master tape handle such fluxivity level?

 

[cdc3oo]

Good summary.

I wonder if that 0.3dB difference has something to do with historic German reference fluxivity measurements that were proven wrong

For those who do not have the Quantegy conversion tool and who don't want to do some math, go to https://sengpielaudio.com/calculator-magneticflux.htm

[edit]Difference is explained in MRL document.

5.2.4.1 Effect of Reference Frequency:
Because of the “standard equalizations” described in §1.2.3 , the flux on a standard Calibration Tape is not usually constant versus frequency even in the range 250 Hz... 1000 Hz. Therefore a change of the reference frequency will produce a change of the reference fluxivity. For example, the Ampex calibration tapes used 700 Hz as the reference frequency, whereas the MRL tapesuse 1000 Hz. When the 7.5 and 15 in/s NAB equalizations are used, the fluxivity on a calibration tape at 1000 Hz is 2.5 % less than at 700 Hz. So the old “Ampex Operating Level” of 185 nWb/m corresponds to approximately 180 nWb/m at 1000 Hz, 260 nWb/m at 700 Hz corresponds to 250 nWb/m at 1000 Hz, and 370 nWb/m at 700 Hz corresponds to 355 nWb/m at 1000 Hz.

How would you even calibrate past the highest mark of 3 on the VU if that is the case?

This requires an AC millivoltmeter connected to the RTR outputs (Leader LMV186A and similar)