+3 Tape Calibration Question.

[pinebox]

Forgive me, I was born in the Pro Tools era.

Every time I think I start to understand nWb/m I read something else and I get confused. I have a 355nWb MRL. I need to calibrate for +3 on a 320nWb reel (ATR Master) Do I calibrate the Repro/Sync VU to 0, +3, or +5 while using the MRL? How would you even calibrate past the highest mark of 3 on the VU if that is the case?

I have looked up and down for a full calibration reference table and have only found partial ones and ones that do not include my MRL fluxivity.

I also googled this exact discussion and found one on Gearslutz saying to calibrate to +0 on the meters, and one on Tape Heads to Calibrate to +3 on the meters.

 

[Brian Roth]

I'm not fully understanding the question. I assume you've already read through the "choosing and using" doc from MRL?

 

[Brian Roth]

Also....does the "320" "ATR Master" tape have test tones recorded on it?

Bri

 

[pinebox]

Thanks Brian, I was referencing that document, and from what I can glean the 355 MRL would mean I aim to cal the meters to +3 referencing 250? I think half my confusion comes from what might be reference creep over the years? Like do I scale the calibration from 185, or 250 or do I do it on individual record reel fluxivity basis?

For instance, do I just use the MRL to get to +3/250 or do I need to have decipher the record reels fluxivity vs the 250 and then scale that to the MRL? Does that make sense?


The ATR Master does not have reference, I need to print those to it.

 

[Brian Roth]

I'm still confused....lol! Why are you using 320 for a new project/cal levels? Stick to 355.

Bri

 

[pinebox]

Im confused too!

I have a 355nWb/m MRL
Client asked me for +3 reference level and handed me an ATR Master Tape which says on their website is 320nWb/m

Where would you cal your Repro to?

Is the nWb/m of the tape being recorded to in the equation at all or is the calibration always in reference to a standard like 250nWb/m?

 

[Brian Roth]

AHA! Now digging into the weeds, as it seems.

https://www.atrtape.com/s/ATR-Master-Tape-Technical-Data-Sheet-Standard-5t95.pdf

That spec sheet (for whatever reason) uses 320 FOR the various other specs. 320 isn't some "magic number"....just a reference level for their specs. Like +4 dBm/+4 dBu in electronics gear.

Client asked for "+3:", but referenced to what? 355? 250? 320? 185? Ya gotta have a reference point....

From there we can work it out.

Bri

 

[pucho812]

Fluxivity varies according to frequency

You have an MRL that was recorded so that you are at 355nWb which is most circles is +6. I say most circles as some tape manufactures will say 370nWb is +6. At least they used to when you had more than a couple of tape formulas and manufactures. The old Ampex standard of 185nW/m was at 700hz; MRL specifies its fluxivity at 1000hz which is 180nWb. The Europeans still specify fluxivity at 700hz, which is why they refer to +6 as being 370nW/m (which it is, at 700hz) vs 355nWb which it is at 1K.
If you take your calibration tape and alignment the machine so that at playback you are seeing 0VU on the frequencies, then you are setting the machine up for a +6 alignment. If you adjust it so that when playing back the test tones, you see +3VU, then you would be setting the machine up for a +3 alignment which is equal to 250nWb. 355nWb is +6, 250nWb is +3 and your 320 is about a +5.

So if he really wants a +3 based on what your OP is, adjust the playback so the meters read +3 and then do your record alignment.

As always check the I/O, next playback alignment and lastly record alignment.

Fo further on alignment tapes.
http://mrltapes.com/choo&u.pdf

 

[Brian Roth]

Pucho....I actually attached "choo&u" above. <g>

Bri

 

[One F Sound]

+3 is an usual request but hey. On PLAYBACK, If you had a 320nwb test tape then when aligning a tape machine for a fresh recording you would set the meters to read 0 for a +4 alignment (this was my circle with respect to pucho812) assuming the meters are aligned traditionally. (this is where my memory fades a bit but I think the meters are set to read 0 with a 0.7v ish signal) Similarly, if you had a 250nwb test tape you'd set the meters for -2 and a 185nwb to -4 on playback. I've not come across a 355nwb MRL test tape in my time and it seems very hot. Is it 1/4", just curious. Then on RECORD, on input you'd send a 0vu signal. Then switch to record and adjust the record trimmers to get 0vu whilst looking at what's coming off the playback head.

And don't forget to do the bias before the record alignment!

What make and model tape machine are you using?

 

[pinebox]

Thank you all very much. I guess my confusion always stemmed from the phrasing of “Plus X over Y” when discussing cal, and wether or not their tape type was also to be considered. It seems like everything would have been much simplified by have one singular reference point.

So this is what I have surmised, and please correct me if I am wrong:

-The tape to be recorded to does not matter in regards to the level requested for calibration.
-185nWb/M=0, 250nWb/m=+3, 355nWb/m=+6 (roughly)
-If someone asked for +3/185, I would calibrate meters to read +3 using the 355nWb/m MRL, which is equivalent to 250nWb/m (3 over 0VU)
-If someone asked for +3/250, I would calibrate meters to read 0 using the 355nWb/m MRL, which is equivalent to +6/185 (6 over 0VU)

Does that track correctly?

 

[pucho812]

Yes that tracks correctly but most will say +6/185, I’ve yet to see anyone say +3/250.
The tape recorded to does matter in that tape formulas have a limit. For example if I was asked to do a +9/185, a level gp9 and 499 can handle, but it was on a feel of 456, the 456 would not be able to handle it and it would too hot for that formula. In turn everything would be distorted.

 

[One F Sound]

Hmmm..... Re. "-If someone asked for +3/185, I would calibrate meters to read +3 using the 355nWb/m MRL, which is equivalent to 250nWb/m (3 over 0VU)" This may be wrong. If you have a 185 test tape and want to be +3 relative to it then you set the meters on playback to be -3. Then when you record your tones (i.e.typically +4dBu input signal reading 0vu on input) you set the record trimmers to 0vu. So with a 355nWb/m test tape which we're saying is +2 to the standard 320nWb/m @0vu then I'd say the meters will be most likely off the scale.

re. "-If someone asked for +3/250, I would calibrate meters to read 0 using the 355nWb/m MRL, " For this I think you'd need to set the playback metering to about +1 with the 355 test tape.

I used to line up tape machines daily but that was aa long time ago and I could be put right here but that's my take on it.

I'm still curious as to an MRL test tape at 355nWb/m. What width is it?

 

[One F Sound]

In addition... when asked for, say, +2 over 250 and you have a 250 test tape. Then on playback you set the meters to MINUS 2. So then on record, in relative terms, you bring it up to zero, thereby making it PLUS 2 over 250.

Hope that helps.

 

[Brian Roth]

Thank you all very much. I guess my confusion always stemmed from the phrasing of “Plus X over Y” when discussing cal, and wether or not their tape type was also to be considered. It seems like everything would have been much simplified by have one singular reference point.

So this is what I have surmised, and please correct me if I am wrong:

-The tape to be recorded to does not matter in regards to the level requested for calibration.
-185nWb/M=0, 250nWb/m=+3, 355nWb/m=+6 (roughly)
-If someone asked for +3/185, I would calibrate meters to read +3 using the 355nWb/m MRL, which is equivalent to 250nWb/m (3 over 0VU)
-If someone asked for +3/250, I would calibrate meters to read 0 using the 355nWb/m MRL, which is equivalent to +6/185 (6 over 0VU)

Does that track correctly?

For +3/185 using a 355 MRL, you would align for -3 VU. I think...lol! Sometimes I get lost as well!

Here's my thinking from a recent event at the studio here. We align for 355 and have the correct MRL tape. I accidentally picked up an older MRL from the shelf that was 250. Naturally, it read -3VU. Hence, +3/185 would be -3VU on the machine previously cal'ed for 355 at 0VU.

Bri

 

[One F Sound]

For +3/185 using a 355 MRL, you would align for -3 VU. I think...lol! Sometimes I get lost as well!

Here's my thinking from a recent event at the studio here. We align for 355 and have the correct MRL tape. I accidentally picked up an older MRL from the shelf that was 250. Naturally, it read -3VU. Hence, +3/185 would be -3VU on the machine previously cal'ed for 355 at 0VU.

Bri

Re. "For +3/185 using a 355 MRL, you would align for -3 VU. I think...lol! Sometimes I get lost as well!" 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). So if you did -3 using a 355 test tape you're going to be running at +3 over 355, but ultimately that equates to +8/9dB over 185. For+3 over 185 using a 355 test tape you need to set the playback to +1Vu.

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!

 

[Brian Roth]

Re. "For +3/185 using a 355 MRL, you would align for -3 VU. I think...lol! Sometimes I get lost as well!" 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). So if you did -3 using a 355 test tape you're going to be running at +3 over 355, but ultimately that equates to +8/9dB over 185. For+3 over 185 using a 355 test tape you need to set the playback to +1Vu.

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!

If you refer to the chart in post #11 in this thread (it's from a MRL publication) 355 is +6 dB over 185.

Bri

 

[One F Sound]

If you refer to the chart in post #11 in this thread (it's from a MRL publication) 355 is +6 dB over 185.

Bri

Exactly. So setting the meters to -3Vu with a 355 test tape results in +9 over 185.

 

[RSRecords]

If you refer to the chart in post #11 in this thread (it's from a MRL publication) 355 is +6 dB over 185.

Bri

Can confirm +6=355nwb MRL aligned at +4dbu= 0vu. Align to 0vu if you're using atr. A very common notation (at least in Nashville) is +3/250. For some reason 250nwb tapes were really common. So this would be aligning the MRL for -3 on the VU and using record touring the signal back to 0 vu.

BTW 355nwb MRL is at 1kHz. This equals 370nwb at 700Hz.

 

[Brian Roth]

Can confirm +6=355nwb MRL aligned at +4dbu= 0vu. Align to 0vu if you're using atr. A very common notation (at least in Nashville) is +3/250. For some reason 250nwb tapes were really common. So this would be aligning the MRL for -3 on the VU and using record touring the signal back to 0 vu.

BTW 355nwb MRL is at 1kHz. This equals 370nwb at 700Hz.

I've been looking at the MRL publications before making further comments .... don't want to offer bad info and embarrass myself! <g> It's been such a rare event in recent times for me that converting operating levels has even come up. But, the MRL docs (written by Jay McKnight, now RIP, who was one of the Giants in analog recording technology design and information) are the "bible" for me and many other folks still using analog tape.

50-ish years ago, when I first started working in studios, the only alignment tapes I knew of (in the USA) were sold by Ampex. The voice announcement said something like "....recorded at Ampex operating level...". No mention of nWb/m, bit it was "185" (-ish depending on the use of a 700 Hz or 1000 Hz reference, as RSRecords mentioned, and discussed in the MRl "Choosing and Using" document).

But, Scotch 206 had become the "standard" tape, and you could print program 3 dB hotter...ie 250 nWb/m. So, from the very beginning for me, I always knew to adjust the 700 Hz tone to -3 VU. Then later with "hotter" blank tapes, set Ampex operating level to read -6 VU.

Anyway, I suspect why folks stuck with the older 250 alignment tapes from MRL or STL (and the corresponding "+3/250" notation on the tape box/track sheet) was the price of purchasing new alignment tapes. Many hundreds of dollars for 2", 1", etc.

@RSRecords One minor quibble... "+4dbu= 0vu" is correct for many pro machines, but not for semi-pro decks...those would be -10 dBV = 0VU. In fact, in older broadcast systems, +8 dBu = 0VU was also common.

Bri