Question regarding recording equalization adjustment?

[jedblue]

In the manual for my Revox PR99, it gives the following instructions for checking and adjusting the recording equalization:

1). Adjust AF generator to 12 kHz, 0VU -20db. Okay, I think I understand that, I check that my tone generator is outputting 12kHz, 0VU -20db using the voltmeter then I input the tone to the recorder (at this time, input calibration, playback calibration, recording level and bias have already been done according to the instructions)

2). Start the machine in record mode. Okay, it's now running with a bulk erased tape on and the volt meter has been attached to the monitor output as instructed.

3). Corresponding to the tape speed, adjust potentiometer EQ SLOW, FAST for an output voltage of 0db to +1db relative to 1kHz. That's the bit I don't understand for an output voltage of 0db to +1db relative to 1kHz. If the tone generator is putting out 12kHz, 0VU, -20db and the voltmeter is connected to the monitor, won't it just be reporting back 0VU, -20db? What's meant by 0db to +1db relative to 1kHz?

Any explainations gratefully accepted.

Geoff

 

[sweetbeats]

Geoff...unless you and I are totally missing the same logic path I'd say there's got to be a typo there...I've struggled with some brain-bending typos in a couple of my Tascam manuals that could only be sorted out by calling up Teac, and even then it took them a bit to figure it out. I'll look in my PR99 manual and see if I can see the inferrence. What version is your PR99?

 

[jedblue]

It's a MKII Cory.

Geoff

 

[ofajen]

3). Corresponding to the tape speed, adjust potentiometer EQ SLOW, FAST for an output voltage of 0db to +1db relative to 1kHz. That's the bit I don't understand for an output voltage of 0db to +1db relative to 1kHz. If the tone generator is putting out 12kHz, 0VU, -20db and the voltmeter is connected to the monitor, won't it just be reporting back 0VU, -20db? What's meant by 0db to +1db relative to 1kHz?

No, remember that when setting HF rec eq, you are recording the signal and monitoring OFF THE PLAYBACK HEAD, not listening to the input signal. So, what you hear will be dictated by total system response: record and playback, not merely a recapitulation of the input signal.

So, this is their suggestion for setting the high frequency record EQ: adjust the control so that the overall system response (signal in to playback of recorded signal) is either flat or up to 1dB higher at 12K versus what it is at 1K. Sometimes manuals say to do this at 10K.

Typically, the system response starts to fall off somewhere above 10K and you have to decide how you want it to go. They are suggesting you keep it roughly flat at 12 K and then take the roll off above that.

You might prefer, and it is perfectly legit, to do this check at 16K, instead. If you tweak the HF rec eq to be flat at 16K, you should have smooth response over a BROADER range, instead of FLATTER response with more high end roll off.

Doing this, though, you are likely to have a bigger peak in system response somewhere in the 8-12K range. If it gets over 2dB, you may want to back off a bit and take some more roll off up around 16K. As is often the case with tape machines, there are tradeoffs and compromises and options to choose. Does that cover it adequately?

Cheers,

Otto

 

[jedblue]

Yes Otto you're quite right and I wasn't very clear about what I meant. I did realise that what I was reading back on the voltmeter was coming off the playback head not the input tone generator. It was the 0db to 1db at 1kHz reference in the manual that was confusing me. I think I finally figured that what they were talking about here was a +/- range not an absolute db value (of 0db). Therefore if I'm inputing 12kHz at 0VU, -20db to the record head then I adjust the EQ trimpots so that the voltmeter attached to the playback monitor reads -20db to -19db, then the equalization will be set all ok.

Yes?

Geoff

 

[sweetbeats]

Man, this is awesome...it seems so confusing, but then if you just do what it says...

I think I get it now.

So the manual is just saying that your 0VU reference point should be set using a 1k tone, and that 12k should be at 0VU or +1VU? This is like the Tascam decks where (when checking record or reproduce eq) it is supposed to be either +/-2dB or +/-3dB (depending on which stage you are checking) from 0VU as referenced to 1kHz. I run tones as specified from 40Hz to 16kHz (IIRC) and set the LF and HF eq so that it is within those specified ranges.

Otto, I get what you are saying...I can easily get my Tascam 58 "flat" (i.e. relatively speaking...like +1/-0.5dB through 20kHz at least at 2k, 4k, 8k, 12k, 16k and 20k), but it doesn't sound right and there is that hump that picks up after 8 or maybe 10k and may be only +1dB at 12k and 16k but who knows what its doing between 12 and 16k, so I'd been shooting for, like, -2dB at 16k and everything seemed to just sit more "right". That was an early awareness for me of the value of using your ears instead of striving for "flat" or "ideal" specs. I can still hear pianodano saying "Yeah, but how does it sound??"

 

[jedblue]

So the manual is just saying that your 0VU reference point should be set using a 1k tone, and that 12k should be at 0VU or +1VU? ??"

I didn't read it quite like that Cory. I've read it to mean that when they say 0db to +1db with reference to 1kHz all they mean is that the playback voltage should be within a range of -0db to +1db of the input voltage at the frequency specified (12kHz in this case), and that's what the reference to 1kHz is about - an acceptable voltage range regardless of the frequency? Maybe we are saying the same thing? They could have equally said "adjust the EQ pots to read -20db to -19db on the monitor voltmeter during playback".

Therefore, if the equalization needs to be calibrated using an input tone of 12kHz at 0VU / -20db, then the EQ pots should be adjusted to show-20db to -19db on the voltmeter when that recorded 12kHz 0VU /-20db input tone is played back.

So the input tone is still 0VU / -20db.

D'oh!!!

 

[jedblue]

Well everything's now done on the Revox and it's humming along nicely doin' what it's supposed to be doing at all the right levels in, around and out.

Thanks for all your help everyone. Tomorrow I'll do the same on the Otari.



Geoff