dumb question about calibration tape and ATR tape

[blungo2]

I'm getting ready to order a calibration tape for my otari mtr-12. We've been running rmgi 900, which i understand is a +9 tape.

I've never calibrated it myself, but i have helped someone else calibrate it and i think i'm ready to try it myself.

I'm thinking that the MRL 355nWb (+6) tape is the right for me. Does that seem right? I'm also thinking of trying ATR tape. Is that a +6 tape? If so, would that mean i calibrate my VU meters to zero?

Sorry for the dumb questions, i'm just trying to get a handle on this stuff. So far, the search function hasn't worked well for me.

Thanks!

[blungo2]

I found this, which seems helpful. I guess i don't understand which reference fluxitivity equals what bias...
I'm guessing 185=0, 500=+9?

[Nick Sevilla]

I'm getting ready to order a calibration tape for my otari mtr-12. We've been running rmgi 900, which i understand is a +9 tape.

I've never calibrated it myself, but i have helped someone else calibrate it and i think i'm ready to try it myself.

I'm thinking that the MRL 355nWb (+6) tape is the right for me. Does that seem right? I'm also thinking of trying ATR tape. Is that a +6 tape? If so, would that mean i calibrate my VU meters to zero?

Sorry for the dumb questions, i'm just trying to get a handle on this stuff. So far, the search function hasn't worked well for me.

Thanks!

Hi blungo2,

The best way to buy an MRL tape, is tocontact these people:

http://home.comcast.net/~mrltapes/

They are the company who makes them, Magnetic Reference Laboratory. Call them and tell them the exact model of tape machine you have, so they can help you in choosing the right MRL tape for calibrating it. DO NOT USE A DIFFERENT TAPE!!!

What you do need to have and understand, is the Factory recommended alignment levels. Do you have the manual? For your initial calibration you should always do it to the fctory spec, for many reasons, like making sure everything works properly, and also to understand better when your machine is actually set up,properly, for when you then decide to use a different formulation, you don't get lost in the maths.

All tape machines have a baseline recommended calibration procedure, recommended by the factory.

And most also tell you how to calibrate the machine for different recording levels, according to the different tape formulations.

Some machines CANNOT USE the newer +9 tapes, so make sure your machine can use that formulation.

As to how to calibrate a tape machine, you should go watch this video IMMEDIATELY:

http://messageboard.tapeop.com/viewtopic.php?t=83027

While this is for a different machine, the procedure is the same, of course, you have to follow your manual to the tee. Basically you will have the MRL tape to do this initial full calibration procedure. This should be done to the MRL tapes reference levels to zero, and will get your machine setup to "Default" settings. If the MRL tape is +3 or +6 or whatever, it will be referenced not only to the correct fluxivity, but also to your machine, as some machines are slightly different to calibrate, like different frequencies than the standard.

And lastly, for when you're ready to get your head exploded by math, there is this:

http://www.quantegy.com/audiorecorder/

[Nick Sevilla]

I found this, which seems helpful. I guess i don't understand which reference fluxitivity equals what bias...
I'm guessing 185=0, 500=+9?

Hi bungo2,

Bias is how "hard" the magnetic energy hits the tape itself, and is related to how deep into the tape your magnetic recording energy needs to go to make a good recording. Bias is referenced to 185 nWb/m =0dBu. On a 185 nWb/m tape, your Bias setting should be zero, or the bias peak, when doing this calibration.

Fluxivity is measured in nWb/m which is nanowebers per meter, and is the measurement of that magnetic energy. It tells you how much magnetic energy that specific tape want to see to make a proper recording.

See the chart? that is all it is telling you where to put your MRL calibration tape level in order to use a DIFFERENT TYPE OF TAPE for recording, which is what you are doing.

So, if your manual recommends you us a MRL tape that is for example, a 250 nWb/m, you would then look at your NEW BLANK TAPE to know where to set your VU meter to.

If you have a blank tape which says it is 320 nWb/m, then you would calibrate your machine using your MRL 250 tape to set your VU levels to -1 dB with the main level frequency. This would then give you the correct levels for that 320 nWb/m tape, which is called +4 since you are +4 dBu FROM THE BASELINE LEVEL OF 0dBu =185nWb/m.

Always remember that the standard fluxivity ZERO VU level is 185nWb/m. Everything else goes related to that baseline zero reference.

Fluxivity = How much magnetic energy to get your VU meter to zero.

Cheers

[blungo2]

Thanks so much! That clears up a lot of things.
Yes, i do have the manuals.

[Nick Sevilla]

Now, for using your "+9" RMGI tape, you have to know that this tape
is referenced to that baseline 185nWb/m.

185nWb/m = ZERO
Your RMGI tape is a 320nWb/m which is a +4 tape, NOT A +9 tape at all.

http://www.rmgi-usa.com/resources/Spec- ... SM_900.pdf

320nWb/m = +4 above that 185nWb/m zero. That is why its called +4 tape.

Because this tape wants a lot MORE magnetic energy in order that a good recording haplens on it. It needs 135nWb/m MORE energy to work properly, than the 185 nWb/m tape.

Does this make sense to you?

Now, to calibrate your machine with an MRL tape which is, for example, 185nWb/m, you would have to set your VU meter 4dB BELOW ZERO, and then when you go to use your +4 tape, when a signal reaches that ZERO VU, it is now using 320nWb/m of magnetic energy to reach that zero VU level. which is how much energy your +4 tape wants in order to make a good recording.

Also, the RMGI reference sheet indicates they are using a BIAS level of -2 dB below Bias peak. This means that you have to set your bias level 2dB LOWER than the Bias peak of your machine. So you go to the peak, and then back it off 2dB from there.

Cheers

[blungo2]

Thanks again, yes it makes sense!

Do you know if the ATR tape is also a +4 tape?

I'm not making much sense of the specs on their page.

http://www.atrtape.com/technical.php

[Nick Sevilla]

Thanks again, yes it makes sense!
Do you know if the ATR tape is also a +4 tape?
I'm not making much sense of the specs on their page.
http://www.atrtape.com/technical.php

Sure,

They have the following specs, for their "master tape":

Maximum linear operating level 9 dB over 185 nWb/m

Which means it is in fact a +9 tape, and this is equal to 520 nWb/m.
You would use your alignment reel to set your VU to -9dBVU when doing
an alignment for this kind of tape on your machine. Once you have set the PLAYBACK side of your machine to this -9 dBVU, the RECORD side will then be set to ZERO on your VU meter. (which is now +9 dB hotter).
What you do is you lower the playback level by the needed amount, and compensate by RAISING the recording level to the right amount. Makes sense?


Recording bias 1.4 dB over @ 20 kHz * using an ATR 102 tape machine.

For other machines use :

Bias Current Recommendation1 10 kHz signal, 15 ips 10 kHz signal, 30 ips

1 mil gap length (ATR-Aria) 1.2 dB 0.5 dB
5 mil gap length (Ampex) 3.0 dB 1.4 dB
.25 mil gap length (Studer) 3.5 dB 1.5 dB

Which means you need to look at your manual in order to find the GAP LENGTH (a number given in mils, or thousandths of an inch) of the recording head.
This is the gap where the magnetic force shoots out and into the tape itself, in the recording head. Use the Bias reference that is nearest to your machines GAP length.
The closest one will be fine, you don't have to go crazy with maths here, just use the number that is closest. On the image below, the GAP is the hole between the magnets, and the magnetic force is in red color, around this GAP.

Cheers

[Justin Foley]

It is sad in life that none of us will ever have the opportunity to pick up the phone, call God Almighty Him/Herself, and get the answer to a question that one may so desperately need. Though all of us face trials and suffering, no one has God's phone number to call and say "what should I do now?".

The closest any human being will ever get to this is to be able to pick up the phone and call Jay McKnight in regards to an MRL-related tape issue. Enjoy the experience of getting the absolute, unassailable right answer to your question when you do so. It's the closest to Omnipotence that you will ever be.

= Justin

[blungo2]

@ Nick. Thanks again! That was very clear. I do believe i'm starting to get this.

@ Justin. I will give him a call!

[honkyjonk]

At one point I called the ATR tape guy. Can't remember his name now. But he's pretty rad too. I was asking him about levels in regards to both the Otari MX5050 (2 track) and Ampex 440B. He said something to the effect, if you can get those machines to do a +9 alignment, go for it. But if you can't, try +6. He mentioned that there is a pretty wide tolerance w/ regard to level for the tape. I tried different bias levels as well and ended up w/ +4dB over at 10K (on the Ampex) Can't remember exactly for the Otari, but I think it was the same. Not saying it is or isn't technically correct according to the head gap on those machines, but that's what sounded best. I have nortronic heads on the Ampex.

[blungo2]

At one point I called the ATR tape guy. Can't remember his name now. But he's pretty rad too. I was asking him about levels in regards to both the Otari MX5050 (2 track) and Ampex 440B. He said something to the effect, if you can get those machines to do a +9 alignment, go for it. But if you can't, try +6. He mentioned that there is a pretty wide tolerance w/ regard to level for the tape. I tried different bias levels as well and ended up w/ +4dB over at 10K (on the Ampex) Can't remember exactly for the Otari, but I think it was the same. Not saying it is or isn't technically correct according to the head gap on those machines, but that's what sounded best. I have nortronic heads on the Ampex.

Interesting. Not having the manual here, i'm guessing the gap width for the MX5050 might be similar to the MTR? If so, i'll try +4 as well as +6, and hopefully +9.
Thanks!

[Jim Williams]

Recommended bias levels are just a starting point. Tape heads vary and wear differently. Every track is a bit off from the others.

The best way I found to 'nail' the bias is to use a THD analyzer. That way you can see the effects of bias on distortion and frequency response. Some rigs allow you to view both at the same time.

You will see a THD vs frequency response curve that looks like a smile. Lowest at 1k hz, much higher at 10 k hz and 100 hz. Some recorders don't like higher tape levels, the electronics have a harder time. Some love it.

I get an MCI JH-110C rebuilt with modern electronics to record flat to 32k hz at 30 IPS. I get THD down from the stock .55% at +3 to .15% at +9 levels. 100 hz and 10k hz still have 4% THD, nature of analog tape.

Besides the low end roll-offs at 30 IPS, the low end THD doesn't sound bad, some like it. 4% THD at 10k hz does bother me quite a bit. That is the sound of cymbals crashing and hats closing. I much prefer quality digital conversion for those sources, 4% THD is too much for my tired ears.
YMWPV

[blungo2]

Very interesting! I'm guessing you have a hardware THD analyzer that i'm assuming is way beyond my means. I wonder if there's a good THD program or plugin around?

EDIT: I found this, which looks like it might work...
http://baudline.com/index.html

[Nick Sevilla]

At one point I called the ATR tape guy. Can't remember his name now. But he's pretty rad too. I was asking him about levels in regards to both the Otari MX5050 (2 track) and Ampex 440B. He said something to the effect, if you can get those machines to do a +9 alignment, go for it. But if you can't, try +6. He mentioned that there is a pretty wide tolerance w/ regard to level for the tape. I tried different bias levels as well and ended up w/ +4dB over at 10K (on the Ampex) Can't remember exactly for the Otari, but I think it was the same. Not saying it is or isn't technically correct according to the head gap on those machines, but that's what sounded best. I have nortronic heads on the Ampex.

Interesting. Not having the manual here, i'm guessing the gap width for the MX5050 might be similar to the MTR? If so, i'll try +4 as well as +6, and hopefully +9.
Thanks!

I think in the end you will not be able to do the full +9, if your machine is really old.
Since you keep posting without the manual by your side, I cannot guess as to what the limits of your machine are.

Keep that in mind and do not go over the limit, in this case it will not sound very good.