Analog tape alignment. Is it too hot?
From: Dana White
+9 on GP 9, 499…BASF 911 Can you comment on why there are multiple reference levels. As I understand it, there is a European standard, consumer standard, etc. When you all talk about levels why is there the intermingling of reference level? Seems to me you pick a reference and stick with it. Perhaps it’s time for a historical primer… Best, Dana
Well, starting with this “+9 thing” I have to assume the Nashville engineers you’re describing know what they’re doing and if only using VUs watch their levels carefully when tracking percussion instruments. To my experience, the GP9 at +9/200 with VUs is less forgiving than the earlier tapes were at lower levels *when using VUs.* I would only recommend +9 to someone who really knows the meaning of headroom and, as you say, use PPMs when tracking and mixing. I wouldn’t recommend +9/200 wholesale to just anyone…only an experienced engineer who knows his meters.
And now for the history!
Historically, the different reference levels on analog tape came from the very phenomenon we are talking about, the increase in MOL (maximum output level) of tapes as the years went on.
First of all, we should all be aware of the formula to convert nanowebers per meter (fluxivity) to decibels. It’s the same as the formula for volts.
20 * log (fluxivity 1/fluxivity 2) = decibel difference.
For example, 6 dB over 200 nw/Meter = 400 nw/Meter
The grandfather of all reference levels is 185 nw/M, going back to about 1950 or earlier. Due to a historical measurement error and possibly a reference frequency discrepancy (some used 500 Hz, some 700 Hz, some 1000 Hz), this has been redefined as 200 nW/M if you follow the logic of Magnetic Reference labs, now the dominant reference standard in the U.S. The difference (if there is a difference) is no more than 0.68 dB between 200 and 185.
By the mid 60’s, tapes capable of handlng 3 dB more level (MOL) were developed. If you round the 0.68 dB error to 1 dB, then we’re talking about either 2 dB hotter or 3 dB hotter than the reference you chose to use. There are no longer any 185 nw/M test tapes being made in the U.S., so we’re de facto at a 200 nW/M reference, and the tapes we call “+3 tapes”, which are at 250 nW/M, are about 2 dB over a 200 nw/M reference. But everyone from the old days of 185 still likes to call 250 “plus 3”. C’est la vie.
In truth, the so-called “+3 tapes”, which are 250 nW/M, are 2 dB up from 200 if you stick to the 200 reference, and 3 dB up from 185 if you stick to the 185 reference. Most people are now used to the 200 nW/M reference, as that is the standard that MRL (in the U.S.) established.
To avoid ambiguity we should always speak nanowebers/meter instead of decibels and specify our measurement tape (MRL)…
But people will use decibels on the tape box because they may be afraid no one will understand what “0 VU= 400 nw/M” means. If marking a tape box, people should include how much hotter they have aligned their tape, and what reference tape they used for alignment. For example, if they used a 200 nW/M test tape and raised it 2 dB, they can write “200/+2” on the box, which unambiguously defines what tape they used, and how far they pushed it. By marking the box with the reference tape they used (200 or 250) and the number of dB they pushed it (+2, +3, +6, etc.), they are unambiguously defining the level of the tape, the standard they originally used, for future generations of users.
“200/+2” is the same as 250, by the way. Thus they might label it “250 nW/M” instead, and leave it at that. Without the reference, a decibel number on the tape box is ambiguous and ultimately means nothing. If I see a box marked “+3”, it means almost nothing to me… Depending on the age of the tape, he might have elevated it 3 dB over 185, maybe 200, maybe 250.
250 nW/M test tapes didn’t come into use until the late 70’s. They have become the standard… I haven’t ordered a 200 nW/M test tape in ages.
As for the “European” standards, 320 nW/M test tapes are fairly common in Europe. Originally these may have been set up for peak meters instead of VU meters, because 320 is 5 dB over 185. This results in a very conservative peak standard for the oldest type of tapes, before the “headroom race” began. You could “pin” the peak meter with a 320 peak reference level and not result in bad sound on the oldest tape types. But nowadays, 320 is a good “average” level for use with a VU, and peaks will be 6 to 12 or 14 dB above that. To be sure you’re not saturating, use a peak-reading meter.
320 nw/M produces a conservative, safe reference level for mixdowns, etc. with modern-day tapes. I use 320 nW/M a lot with BASF 911, when I have to go to 1/2″ and all I have is a VU meter. You could push it more with GP9, but I don’t think that is necessary with 1/2″ 30 IPS, the noise is quite low even a 320. And there is less saturation, the tape sounds cleaner at 320. Push it more, and you are using the tape’s saturation as a processor, which is perfectly legitimate. Just be sure to listen to the repro head while recording to make sure you like the sound of this processor.
I hope this helps,