Here we go again...MRL tape eq, fringing, etc...

[sweetbeats]

I'm about to set azimuth on my 388.

My MRL tape is the one I bought for my BR-20T, a 21J203 (250nWb/m 15ips IEC multi-frequency tape).

1. The MRL catalog lists this as a tape that does NOT have fringing compensation and if you are using it with a stack with track widths or 1~2mm you should order one with fringing compensation...so...can I NOT use this with my 388???

2. The 388 specs are not clear what the eq standard is...in the specs it says IEC/NAB/DIN...:???:...anybody know?

Arg.

 

[thinbrownline]

Hi Cory

1. Your 388 will be IEC - all the Tascam machines were.
2. Fringing only affects low frequency, so use the tape to adjust above 1kHz only.
3. In any case you should align the low frequency by recording your own tones on the 388 (but not onto the test tape, ha ha!). This is a standard recommendation for multitrack machines, not specific to your machine or this version of the test tape.

Have fun!


Regards


David

 

[sweetbeats]

Thanks, David!

That makes sense...all the Tascam machines I've worked with were indeed IEC, but this is my first 1/4 inch 8-track and the manual (unlike my other Tascam decks) was not specific...but it wouldn't make sense to run NAB at 7.5ips...or at least it wouldn't be consistent I guess.

So my 15ips tape will work for azimuth (using the 20kHz tone) and for basic level set (using the 2kHz tone)...but nothing under 1kHz huh?

Maybe I'll get a compensated tape at some point. It'd be nice to check the LF response at some at some point.

 

[thinbrownline]

Cory

I wouldn't bother with another test tape. MRL never compensated for narrow gauge machines, only for professional track widths, and even then it was only approximate.

Like I said, check your LF by recording your own tones.

You will notice that there is no adjustment for LF EQ on the record side of any tape machine, only on the repro side. That's because the LF side is unaffected by different tape formulas or bias settings, only the HF.

Regards


David

 

[Tim Gillett]

Cory, David's quite right here. Besides, strict azimuth alignment to the standard is only important if you're playing back the tapes on another machine which would I assume to be highly unlikely in your case, and generally today.

And azimuth alignment with 8 tracks on 1/4" at 15ips is not at all critical. It might be important if you have identical audio material recorded on outside tracks such as track 1 and 8, and then you sum them, as you might get some phase cancellations but apart from that, azimuth alignment on this format is not something to get too worked up about.

As a point of comparison, try azimuth alignment on 1/4" half track stereo at 15/16ips. Just breathe on the play or record head and it would drift out. Well almost anyway...About 50 times more critical than with your 388!

The acuteness of azimuth alignment is proportional to track width and inversely proportional to tape speed. So as an equation

A=track width
tape speed

You can always play the test tape to check LF as a general indication. You should look for consistency between tracks, not an absolute value. Also, you should probably expect the outside two tracks (1 and 8) to have less fringing effect than the others because unlike the others they only have a fringe on one side of their track gap rather than two on all the others.

Ah the joys of analog tape maintenance and alignment.

Cheers Tim

 

[sweetbeats]

Tim and David, thanks.

Just to be clear, the 388 is not a 15ips machine...it is a 7.5ips machine only.

And I wasn't planning on trying to set LF record EQ, but to monitor the repro response to see if my 388 is "in spec" according to the range in the manual.

What you are saying makes a lot of sense now though...looking ahead in the manual a bit I see that the 388 does only feature HF eq trimmers for the record and repro side and no LF trimmer for the repro side like my 48 and 58 had. So its fixed and once the tracks are setup consistent with each other at 1kHz and 10kHz then its will indeed be a simple matter of tracking a variety of LF tones at a known level and then noting the response levels, but there will be little I can do about it if it is off-spec except swap cards around to see if the issue follows the card. My hunch is that everything is going to be A-OK.

Regarding the azimuth, I do still want to check it. I imagine it is probably well and good-enough...the headblock was lapped and aligned by JRF at some point in its life and so far every other mechanical adjustment I've checked on this machine has been in spec so...

It is all fun though, and it is feeling pretty good to be getting back to this stage of a refurb rather than chasing down phantoms in the "works".

 

[Tim Gillett]

Cory, my mistake. I must have seen the 15ips referring to your test tape and assumed the 388 was also 15ips. But even at 7.5ips, azimuth will not be touchy at all. Tim

 

[thinbrownline]

I had also not twigged that you had a 7.5ips machine. Reading through again I see that it is only the test tape that is 15ips.

The good news is that, believe it or not, IEC test tapes can be used at any speed! Just check out the MRL "Choosing and using..." document on their web site. Of course, when you use a test tape at half speed, the HF only goes up so far....

Regards


David

 

[sweetbeats]

Regarding HF limit, yep...fortunately it is the multi-frequency tape with the 20kHz tone so at least I've got my 10kHz tone for basic azimuth and at least some over consistency of HF repro response...I'll have to get them all the same and then just use my ear to taste as far as where I set it since I won't be able to adjust to spec, though I suppose once they are all the same I could also record some 12kHz or 14kHz tones just to get an idea of what's happening up "yonder".

 

[evm1024]

Nab

I would be willing to bet that your machine is NAB (unless you got it in japan or europe). Look at page 1-3 of the Mant section where it says use a NAB test tape and correct for the different flux.

Looking over the parts list I only see the one head where as some manuals list different heads based on EQ.

So if you start finding that it does not calibrate like you think it should IEC then switch over to NAB.

or you could mod it to take IEC.... But you need to finnish some projects before starting another

--Ethan

 

[sweetbeats]

Oooooo...ANOTHER PROJECT!! YAHYAH!

oh...right...okay. Yeah. I guess I should wrap up 1 or 2 or 5 projects first...actually I know...I'll run it NAB and enjoy it the way Tascam intended.

Now, WHERE is the NAB/IEC conversion table?

 

[evm1024]

That table hides out....

But here it is:

CONVERSION TABLE FOR DIFFERENT SPEEDS AND EQUALIZATIONS
Normalized to the 1000 Hz Recorded Fluxivity
Calibration Tape 10: 15 in/s, IEC (IEC1) Equalization
Desired Playback 8: 7.5 in/s, NAB (IEC2) Equalization
Recorded Playback Playback
Frequency/ Frequency/ Level/
[Hz] [Hz] [dB]
32 16 -10.18
63 31 -5.32
125 62 -2.01
250 125 -0.51
500 250 -0.05
1000 500 0.00
2000 1000 -0.23
4000 2000 -0.90
8000 4000 -1.87
10000 5000 -2.12
12500 6250 -2.32
16000 8000 -2.48


Gotta put in your own tabs to line it all up....

--Ethan

 

[sweetbeats]

Okay...so...just interpolating here.

So if I put the 15ips tape on the 388 and playback the 1kHz tone (which will be heard as 500Hz because of the 388's 7.5ips transport speed) and the meter shows 0VU, and then I reproduce the 2kHz tone (which will be heard as 1kHz) and the meter shows "-0.23VU" that is really "flat" even though the reproduce level varies from one tone to the next when using that test tape on the 388?

And to extend this, if I then reproduce the 16kHz tone (heard as 8kHz) and the meter shows -1.48VU that means I am 1dB above my reference set at the 1kHz tone (that I heard as 500Hz) right?

Does the chart go up to 20kHz?

 

[evm1024]

Okay...so...just interpolating here.

So if I put the 15ips tape on the 388 and playback the 1kHz tone (which will be heard as 500Hz because of the 388's 7.5ips transport speed) and the meter shows 0VU, and then I reproduce the 2kHz tone (which will be heard as 1kHz) and the meter shows "-0.23VU" that is really "flat" even though the reproduce level varies from one tone to the next when using that test tape on the 388?

And to extend this, if I then reproduce the 16kHz tone (heard as 8kHz) and the meter shows -1.48VU that means I am 1dB above my reference set at the 1kHz tone (that I heard as 500Hz) right?

Does the chart go up to 20kHz?

These are from a file I got From jay...

You would set your playback level at 1 kHz (that you hear which is the 2 k tone at 15 ips) to read -0.23 VU. Then because you don't have a 20 kHz to play back at 10 (or do you?) you could set HF EQ at 8 kHz.

Or you can graph out the curve and estimate....

--Ethan

 

[sweetbeats]

My tape does have a 20kHz tone, so I get to make a graph. Cool.

So, assuming "0VU" corresponds to the reference level of the MRL tape I'm using (which in my case it should as the 388 is standardized on 250nWb/m and that's the tape I have) I should:

1. set the repro level to be -0.23VU when reproducing the 2kHz tone (heard as 1kHz)
2. reproduce some other higher frequency tones to monitor the response
3. Again, if the VU meter shows -1.48 when reproducing the 16kHz tone (heard as 8kHz) then that is the same as +1 over the "0" reference (i.e. -0.23) at 1kHz (i.e. when reproducing the 2kHz tone on the 15ips tape), right? Because "0" at 8kHz on an NAB 7.5ips machine is gonna look like -2.48VU using an IEC1 15ips MRL tape, and if the VU shows -1.48VU instead, that would show up as +1VU if I was using the proper NAB 7.5ips MRL tape right?

 

[evm1024]

er, sorry, I was in Astoria.

Yes if it reads -1.48 VU when it should read -2.48 VU then it is 1 dB too hot and needs to be adjusted down.

-Ethan

My tape does have a 20kHz tone, so I get to make a graph. Cool.

So, assuming "0VU" corresponds to the reference level of the MRL tape I'm using (which in my case it should as the 388 is standardized on 250nWb/m and that's the tape I have) I should:

1. set the repro level to be -0.23VU when reproducing the 2kHz tone (heard as 1kHz)
2. reproduce some other higher frequency tones to monitor the response
3. Again, if the VU meter shows -1.48 when reproducing the 16kHz tone (heard as 8kHz) then that is the same as +1 over the "0" reference (i.e. -0.23) at 1kHz (i.e. when reproducing the 2kHz tone on the 15ips tape), right? Because "0" at 8kHz on an NAB 7.5ips machine is gonna look like -2.48VU using an IEC1 15ips MRL tape, and if the VU shows -1.48VU instead, that would show up as +1VU if I was using the proper NAB 7.5ips MRL tape right?