+6 tape +5 dolby what does this mean??

[Blue Jinn]

Hello,

Posted this on the Tascam forum too. Somewhat new to this as far as the technical aspects go. Have a couple of Dolby units to use with a mastering deck. (Expecting a Tascam 42 for that, currently an A-3300SX.) And yes the older Dolby units are pin 3 'hot'.

The Dolby manual says to calibrate use either the NAB or the DIN level on the dolby meter, the NAB corresponding to 185 nWb/m (0dB) or DIN 320 nWb/m (+5dB). My tape of choice is Quantegy/Ampex 456 (370 -- +6) and will bias new deck for that. So what if anything does this mean? Do I just go through the calibration and make sure 0 = 0 all around? Use the DIN scale and assume it is OK, use the DIN scale (+5) on the dolby unit and compensate with -1dB on the deck. (So that 0 dolby = -1 on the deck) Or should I bias the deck at 320 nWb/m (+5db) or what? And if I bias at 320 can I still use 456? (Seems to be so if I can use 406 on the same deck...)

I admit, I still don't quite get what it means that e.g. 406 and 456 are "bias compatible" but that 456 is "hotter" (I am assuming that means I can peak to +6 on the VU without distortion while using 456, but don't have the same headroom using 406.)

Any insight much appreciated.

 

[RRuskin]

Hello,

Posted this on the Tascam forum too. Somewhat new to this as far as the technical aspects go. Have a couple of Dolby units to use with a mastering deck. (Expecting a Tascam 42 for that, currently an A-3300SX.) And yes the older Dolby units are pin 3 'hot'.

The Dolby manual says to calibrate use either the NAB or the DIN level on the dolby meter, the NAB corresponding to 185 nWb/m (0dB) or DIN 320 nWb/m (+5dB). My tape of choice is Quantegy/Ampex 456 (370 -- +6) and will bias new deck for that. So what if anything does this mean? Do I just go through the calibration and make sure 0 = 0 all around? Use the DIN scale and assume it is OK, use the DIN scale (+5) on the dolby unit and compensate with -1dB on the deck. (So that 0 dolby = -1 on the deck) Or should I bias the deck at 320 nWb/m (+5db) or what? And if I bias at 320 can I still use 456? (Seems to be so if I can use 406 on the same deck...)

I admit, I still don't quite get what it means that e.g. 406 and 456 are "bias compatible" but that 456 is "hotter" (I am assuming that means I can peak to +6 on the VU without distortion while using 456, but don't have the same headroom using 406.)

Any insight much appreciated.

As far as I know, the 3300SX and 42 machines were spec'd @ 250 nWb/m. I would set the "0vu" value for that fluxivity and then use the same "0" throughout the chain.

 

[sweetbeats]

Yah...what he said. If you are using noise reduction it is better to cal the deck for the 250nWb/m (those decks...), and the Dolby unit "calibration" is just to make sure that your signal going in (whether it be -10 or +4) comes out the same going to and from the deck.

Does that make sense?

You're just trying to make sure that the n/r unit doesn't effect what reads as "0" coming off your mixer when tracking, and what reads as "0" on the deck when reproducing.

 

[Blue Jinn]

So if I am following this correctly, bias the deck (expecting this to be the 42) for Ampex 406 (+3dB 250nWb/m) and make sure that 0 = 0 = 0 all around?

What I don't follow is why the Dolby units have two different calibration points on the Dolby meter NAB (OdB) and DIN (+5dB). I am assuming I adjust the trimmers on the Dolby unit to keep everything at 0 VU and it does not matter which scale is used as long as the adjustments result in 0 all around.

Thanks!

 

[RRuskin]

So if I am following this correctly, bias the deck (expecting this to be the 42) for Ampex 406 (+3dB 250nWb/m) and make sure that 0 = 0 = 0 all around?

What I don't follow is why the Dolby units have two different calibration points on the Dolby meter NAB (OdB) and DIN (+5dB). I am assuming I adjust the trimmers on the Dolby unit to keep everything at 0 VU and it does not matter which scale is used as long as the adjustments result in 0 all around.

Thanks!

1. Use whatever tape you want @250nWb/m.
2. Use NAB point to Cal 0 on the Dolby.

 

[sweetbeats]

Blue Jinn...

There are really three things you are dealing with here and you've got to separate them out:

• Tape deck electronic calibration
• Tape deck biasing
• Dolby unit calibration

Read this thread:

https://homerecording.com/bbs/showthread.php?t=262644

It might be helpful. I understand your confusion as I was in the same spot just months ago.

The main point for you is that you need to separate the tape classification (+3, +6, +9, +whatever...), and the operating level to which you calibrate the deck.

The +3, +6, +9, +whatever rating of the tape has to do with how hot a signal that tape can handle before reaching a predetermined level of distortion, typically 3%...that's the industry standard for the distortion level elicited at the tape rating.

The operating level (which you decide and set when you calibrate the record/repro electronics of your deck) has to do with "what does 0VU on meters mean?"

Okay? So...pause...think...like Rick said in the last post you can use whatever tape you want...the +3, +6, +9, +whatever rating of the tape has nothing to do what what operating level you have to set the deck.

456 and equivalent tape can handle "+6 over" the old ampex standard of 185nWb/m. That used to be the standard. That was "0". Then the industry started developing higher output tape...+3 (250nWb/m...like 406 tape), +6 (370nWb/m...like 456 tape) and so on.

So when you are calibrating your record and reproduce levels ("calibrating" the deck's electronics) you are simply setting your deck up so that your meters reference "0VU" at a signal strength that fits for your setup. The way Tascam setup the 40-series decks (as well as many others) was to run +6 tape, and to have the record-repro electronics calibrated to +3 (250nWb/m) so that when the meters show "0VU" the signal is still -3VU from the +6 ~ 370nWb/m ~ 3% distortion level of 456 tape. In other words, if you cal a 42 deck to 250nWb/m, at 0VU you will still have 3VU of headroom before your hitting the tape hard enough to elicit 3% distortion. Mind you, tape distortion is considered "good" at low levels. 3% distortion is not a muff box. It is third-order harmonic distortion...yummy.

Bias is a whole separate part of the "calibration" process. The tape oxide needs to be "excited" in order to effectively receive the signal from the heads. The way the oxide is "excited" is that a bias signal is introduced to the tape. The frequency of the bias signal on the 42 is probably 150kHz. You can't hear it, but without it your recordings will sound like rubbish. "Biasing" the deck is simply tweaking the bias level trimmers for each track so that there is enough bias signal, but not too much.

Then the third thing you are asking about is the "calibration" of the Dolby unit which, yes, as you reiterated, that is just a simple level calibration to make sure that what goes in is what comes out level-wise.

Hope that helps.

Now go read the linked thread...