Important Tape Calibration Question

[A Reel Person]

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Ah yes my bad, I forgot that machine i/o's at -10 not +4db, so make sure you're sending your cal tones out at that level.

This spec refers to -10dbV=0.316V on the inputs/outputs of the deck, -10dbV line operating level, which is separate from -10VU on the meters.

 

[A Reel Person]

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The manual calls for +3 or the same as your 250 nWb/m cal tape. So using that tape you would set VU meters @ 0 VU

Puts +6 MOL @ +3VU on the meters.

The line level for each channel is separate and should be set to –10 dB.

-10dbV = 0.316V on the DVM when measuring line levels on inputs/outputs.

 

[thereelman77]

Well, by MOL what do you mean?

So basically with the deck calibrated at -3vu, I would hit distortion above 0vu?
With it calibrated to 0vu, I would hit distortion above 3vu?

 

[A Reel Person]

...

Well, by MOL what do you mean?

So basically with the deck calibrated at -3vu, I would hit distortion above 0vu?
With it calibrated to 0vu, I would hit distortion above 3vu?

Maximum Operating Level
Yes
Yes

 

[thereelman77]

Alright, then I have the deck calibrated to 0vu currently.

I got confused by that concept of +6.

I understand the -10db and +4db difference, my main concern is doing the BIASing right now.

As I had posted before, I'm not getting needle drop when turned completely counter-clockwise.

 

[A Reel Person]

Not sure which deck you're focusing on ATM, but either way,...

try lowering the output of the signal generating device. It's not so much where you are on the VU meter at this point, as it is essential to see the "peak" and "drop".

 

[A Reel Person]

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Alright, then I have the deck calibrated to 0vu currently.

I got confused by that concept of +6.

I've seen this misconception perpetuated all over the interwebs, even on "pro" info sites.

 

[thereelman77]

Ohhk.

So where the meter is, is irrelevant?

Channel 1 could peak at +3db and Channel 2 could peak at -2db, but as long as I drop them 3db that is all that matters?

 

[A Reel Person]

...

Ohhk.

So where the meter is, is irrelevant?

Channel 1 could peak at +3db and Channel 2 could peak at -2db, but as long as I drop them 3db that is all that matters?

Yes, exactly.

 

[thereelman77]

Yes, exactly.

DUDE.

I'd shake your hand right now, but this has been throwing me for a loop for the past day.

I thought that their was a relevancy, but as long as it drops 3db that is all that matters.

Alright, I'm going to give this a whirl now, I have my computer next to the deck, ready...

 

[briank]

try lowering the output of the signal generating device. It's not so much where you are on the VU meter at this point, as it is essential to see the "peak" and "drop".

Right, You can't look at a VU meter and "know" what the overbias is set at. It's all relative, the overbias is determined by how many dB below the peak reading you go as you turn the bias trimmer clockwise and the meter dips. As I said, the peak reading of each channel will be a little different, that's pretty typical, it's all relative. If you can back off the trimmer and get a peak reading, but can't get the meter to go back down to set correct overbias then that's peculiar.

Let's back up a little and make sure your VU meters are calibrated properly. When the meters are set to show input level, you should be able to send your -10dbv levels (confirmed at the jack as 0.316vAC with a volt meter) and see 0VU on the meters in input monitoring. Assuming those are correct, carry on with the calibration. I'm not sure how prone this is to drifting on the Tascam decks, but thought I'd bring it up since you won't get reliable meter readings if the meters themselves aren't calibrated to the standard of -10db levels = 0VU on the meter.

 

[thereelman77]

Alright, well I went thru and biased the deck, it seems to have worked.
But I'm going to walk you guys thru what I have done, to make sure I'm doing it correctly.

To back track what I have done:

1. Calibrated Norm/Monitor Playback levels and EQ to all be set at 0vu. The Teac does not have a LF EQ so, I just did the HF only.

2. Biased the deck, by running my test tone CD thru my mixer, with outputs reading 0db (on the mixer) and running that directly into the Teac. I then set the input gain knob on the Teac so that the meters all registered to 0vu. NOW this is where it may get a bit confusing, because I read the directions from the manual on how to calibrate the deck, and the machine is slightly different from what directions briank gave me. Putting the machine in calibration mode (recording on the tape, then switching to Monitor/Norm at the same time) I adjusted the BIAS level, by dropping (according to the manual) 3db from the point of peak. I did this on all 8 channels.

Now I believe that I made a mistake, by setting my mixer output to 0db, would that not be considered +4db REF #? Would it just be worth me plugging my CD player directly into the teac decks inputs (RCA to RCA), I would think that would be much easier (except for the fact that I can only do 2 channels at a time).

3. Run 1kHz @ 0vu and adjusting the REC/GAIN levels.
Now the problem I ran into here, is that, you guys and every other walk through online says to adjust the HF EQ and LF EQ using 10kHz and 100 Hz, but my deck does not have either of those EQs for the input. I only have a REC EQ. And according to the manual I can only adjust that running an 18kHz tone and adjusting that pot. So...I downloaded a tone generator and ran that thru my mixer into my recorder and attempted to adjust it.

This is where I am at currently. My big questions: did I screw up anything by not running my tones correctly thru my mixer and would it better for me to run directly from the CD player into the tape deck?

 

[miroslav]

You might be OK...but then, "0" on your mixer may not tell you exactly what the actual level/voltage is.

I always like to use a DVM to check all my levels, though I also have a nice little box that puts out specific levels and frequencies, so I know what I have and what I'm putting into the deck when setting things up.

If you have a DMV and you know which reference levels you wanted to use...just check the output levels as you had things set up. If they are hitting where they should be...then no reason to go back and redo stuff.
Worst case, if you were off by any amount...the DVM will tell you how much, and you can then chose to leave the deck as-is and simply be aware of that level difference...though if there was one, I'm sure you will want to go back and recalibrate.

 

[thereelman77]

Well, to be honest, I don't think the mixer is an issue. It seems that all levels are matching up. The only section I'm having issues is the REC input FR EQ, running the 18kHz (according to the Teac manual) something they really kinda skimped on, by not putting HF and LF EQ adjust. I have been going thru, fine tuning the calibration, checking frequencies con-currently. I do have an VM, but it is analog and I have no clue how to set it up and use it. I'm more concerned getting this 18kHz tone together. Then testing, since at the moment, I don't have any huge recording jobs coming up.

 

[thereelman77]

So, as of now, I have followed the manual and all of what has been told to me. So, to the best of my knowledge, the deck has been calibrated, excluding head alignment and azimuth.

 

[fgonza2]

Now the problem I ran into here, is that, you guys and every other walk through online says to adjust the HF EQ and LF EQ using 10kHz and 100 Hz, but my deck does not have either of those EQs for the input.

So, as of now, I have followed the manual and all of what has been told to me. So, to the best of my knowledge, the deck has been calibrated, excluding head alignment and azimuth.

Your deck is not calibrated. Heads and azimuth are a big part of it, if you have the deck since new, the chances of those being off is less, but still, as these decks have years and years they are likely in need of calibration, basically due to age and mechanical drift which can be caused by simple things such as transportation. Also with time, heads wear out and in order to compensate for that wear you need to adjust the electronics.


There are two reasons of why you need to calibrate a deck:

1. Optimize it for less noise, better freq response & dynamics. In other words make the most out of the deck based by haveing the electronics perform at "spec" meaning the best possoble operation and quality.

2. Be compatible with other decks, meaning you taking your tapes to others or taking tapes recorded in other decks. Over time people change equipment or the recorder goes out of adjustment. So having a well known reference and your decks set to it ensures that you can always come back to your recordings and listen to them with the quality and content that you expect them to be.

In order to know if a deck is calibrated or to calibrate one. You need an RMS meter and an MRL or calibration tape as a minimum and a scope is highly desired. The 1khz and 10khz adjustments are using an MRL tape, so you set the repro/sync playback levels and EQ. After that is set you move into biasing and rec level/eq. Without the playback levels adjusted anything that you do on BIAS and rec calibration is relative and for sure off the optimal values.

This is referring only to the electronics side. Remember that the transport also needs some basic maintenance and can cause a lot of trouble too.

Having analog recorders unfortunately is not cheap. It is totally worth considering on buying MRL tapes and some basic equipment, that will make sure your equipment is in optimal shape and you will always make the best out of it. You wont regret those investments and if you love analog sound and tape recorders you should invest in that, you won't regret it.

 

[briank]

Well, to be honest, I don't think the mixer is an issue. It seems that all levels are matching up. The only section I'm having issues is the REC input FR EQ, running the 18kHz (according to the Teac manual) something they really kinda skimped on, by not putting HF and LF EQ adjust. I have been going thru, fine tuning the calibration, checking frequencies con-currently. I do have an VM, but it is analog and I have no clue how to set it up and use it. I'm more concerned getting this 18kHz tone together. Then testing, since at the moment, I don't have any huge recording jobs coming up.

Well, let's help you get that volt meter in the picture. You need to know if you're sending the cal tones into the machine at the right level. If you're not comfortable with your analog volt meter, any basic digital one will do, it needn't be anything fancy, a $15 Radio Shack DVOM will do the trick for basic measurements.

 

[jpmorris]

Well, let's help you get that volt meter in the picture. You need to know if you're sending the cal tones into the machine at the right level. If you're not comfortable with your analog volt meter, any basic digital one will do, it needn't be anything fancy, a $15 Radio Shack DVOM will do the trick for basic measurements.

Aren't they inaccurate over 400Hz?

 

[thereelman77]

I mean, I'm comfortable to use it, but if you mean if I am comfortable in understanding it, I am not. I would need to know how to plug it into the deck and what settings to turn it too. That's all. And to back track, I got the 18kHz tone EQ setting to work. The manual states that, as long as I have set that frequency the closet to 0VU, that's the most I can do. All the channels are either on 0vu or hovering just below/above it.

I downloaded a freeware oscilloscope, just to see my signals thru the machine when running the MRL tape. They all appeared to be equal.
Just as well, all my inputs/outputs are a lot more equal-leveled now. I played back a tape I previously recorded on, pre-calibration, and, believe it or not, it sounds brighter and less noisy. I attribute the brightness to the demag, but the noise?? I assume the calibration made a difference. All around it sounds "cleaner", if you will, so to my own ears, it sounds like the calibration helped it out a lot.
Now whether or not it is correct on paper, that I'm not sure of.
I would like to try the VOM out, I just don't know what to set it too and where to plug the cables into on the in/out channels.

But also, I'm trying to get MRL for my 2 track, just to have that ready for that deck. This is what I am looking at: http://usrecordingmedia.com/mrltwosp1mrl.html ... is this a correct choice for my Otari deck?

Let me know, thanks.

 

[miroslav]

I mean, I'm comfortable to use it, but if you mean if I am comfortable in understanding it, I am not. I would need to know how to plug it into the deck and what settings to turn it too. That's all.


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I would like to try the VOM out, I just don't know what to set it too and where to plug the cables into on the in/out channels.

It's appears mind-boggling the first time...(been there, done that)....but it's not that complicated and there are a few guys here who can guide you step by step...but you first would need the tools in-hand.

I've used some soft-scopes and soft-meters...and they can be used, but I found they didn't work/feel quite right for some tasks.
I then took a deeper plunge and got the hardware scope, already had a good DVM, got the tension testing tools, got a cool (old) digital audio level and frequency tool (got it for like $20, great deal), got the spring scales, got the W&F meter....and MRL tapes for 3 different decks....
...and it all made the calibration process easier and more accurate.

Granted...when you have maybe one deck, or just a passing interest....it seems a little nuts to drop all that $$$ for all those tools...just so you can do the occasional calibration.
I was already in pretty deep and now have 1/4", 1/2" and 2" decks...so for me the right tools became an absolute necessity.

Hey...where the heck are you located?
Maybe there's someone here close to you that can help out on some things so you don't get in too deep and too lost...?