Anybody ever cal their record eq this way?

[sweetbeats]

So in a moment of mental drift this evening I wondered if anybody has ever adjust their record eq this way:

Record pink noise and monitor off the record head with a spectrum analyzer and tweak away.

At least with my Tascam decks the methodolgy is to record tones over a predetermined range and adjust the response at those tones so the deck is within the specified range (like + or - something or other dB's from 40 ~ 20,000Hz or something like that). So why not just hit it all at once with pink noise and look at the response curve in real time?

 

[cjacek]

Hey, Cory, we're on the same wavelength. Now, I understand that there's a difference between pink and white noise but I'm pretty much convinced of using the latter for bias adjust. I see no reason not to use pink noise for EQ. It may not be textbook but, heck, I see no reason not to try and if your ears are good and you can match source vs off tape, then you've just adjusted your recorder, more or less, to precisely capture complex frequencies, found in music material.

 

[ofajen]

So in a moment of mental drift this evening I wondered if anybody has ever adjust their record eq this way:

Record pink noise and monitor off the record head with a spectrum analyzer and tweak away.

At least with my Tascam decks the methodolgy is to record tones over a predetermined range and adjust the response at those tones so the deck is within the specified range (like + or - something or other dB's from 40 ~ 20,000Hz or something like that). So why not just hit it all at once with pink noise and look at the response curve in real time?

MRL does sell playback calibration tapes that use sweeps along with scope charts that let you do something similar in terms of looking at response over the whole spectrum at once.

A couple of things to mention about your suggestion:

1) pink noise or 1/f noise falls off at 3 dB/octave, so you'd need to compensate for that, while white noise would give constant sensitivity across the frequency band.

2) you would, of course, monitor off the playback head, not the record head.

3) there may be an issue with momentary level fluctuations in the noise that would make it more annoying than using a single tone if you are, say, setting the overall response precisely flat at 16K and then checking for tenths of a dB deviations above the reference level in the region around 10K.

Just thinking out loud. No harm in trying it, of course.

Cheers,

Otto

 

[sweetbeats]

heheh...duh...yes. Monitor off the repro head.

I thought pink noise was the flavor that represented more real-world sound energy with more even energy across the spectrum vs. white noise with energy represted at regular frequency intervals...? Time to refresh on that one. But that was my goal anyway and if that'sw hite noise then that is what I'd be talking about.

Also, the software-based analyzer I'd be using has settings for peaking vs. averaging and slow vs. fast response rates and I'd probably set it for averaging with a slow response rate...

 

[Herm]

Cory how would you do that with a latter machine. Like the 30, 40,,50series tascams since they are 3 head machines.
Teacs could do that but the freq response on them is terrible comming off of the Record head. Also The sync head on the 20 series is bad compared to the play head.

 

[ofajen]

I thought pink noise was the flavor that represented more real-world sound energy with more even energy across the spectrum vs. white noise with energy represted at regular frequency intervals...? Time to refresh on that one. But that was my goal anyway and if that'sw hite noise then that is what I'd be talking about.

It may be possible either way, if the analyzer has several ways of showing data. Pink noise has equal energy per octave band, so if your analyzer is showing you "bins" with energy in some constant fraction of an octave, pink noise may be the easy way to go. It probably depends on how your spectrum analyzer is set up. I was thinking in terms of the fact that for the purposes of calibration, you actually want to check constant levels at all frequencies, which is what white noise provides. You are right that real world sound energy spectra are more pink than white, which is why 0 dB at 20K is a LOT of 20K! But for calibration with tones, you do use constant level for all frequencies.

Cheers,

Otto

 

[cjacek]

If I understand correct, white noise contains every frequency within the human hearing range in equal amounts. Would it not be a plan then to use that noise for not only bias adjust but also for EQ adjustment? I'd pump white noise into the recorder, via line in, set it to record and, while monitoring via the play head, adjust the parameters so that source = off tape. Again, does that make sense? Kinda a poor mans way but it should work fine, at least that has been my limited experience.

 

[ofajen]

If I understand correct, white noise contains every frequency within the human hearing range in equal amounts. Would it not be a plan then to use that noise for not only bias adjust but also for EQ adjustment? I'd pump white noise into the recorder, via line in, set it to record and, while monitoring via the play head, adjust the parameters so that source = off tape. Again, does that make sense? Kinda a poor mans way but it should work fine, at least that has been my limited experience.

Sorry, but this will NOT give you any useful calibration. First, for biasing, you need to adjust for a particular level of sensitivity drop at a particular frequency, say, .2 dB at 1K or maybe 3 or 4 dB at 10K, depending on the tape and where you want to be on the output, distortion and noise curves. Using all frequencies at once won't really tell you anything, because the response is different at different frequencies. Put another way, given that you are slamming the tape with all frequencies, what are you going to choose for sensitivity drop?

Similarly, for record eq, merely monitoring off the tape with the SVI won't tell you anything, because it is a single value averaged over all frequencies. How would you know if it was too strong at 10K? Too weak at 1K? Too much dip at 120? Too much hump at 60? No way to know what frequencies are strong or weak. You need a spectral analyzer that scans and reports a value for all different frequencies or at least a set of frequency bands.

Taking this little Otari 8 track I've been tweaking as an example, I honestly don't find it takes that long to adjust playback off of the standard test tone tape (maybe 10 minutes or so?) and then adjusting level, (HF) eq (typically flat at 16K works fine) and low playback compensation (balance the dip at 120 vs peak at 60) for record with a tone sweep just to check things out is maybe another 10 minutes on the record side.

Cheers,

Otto

 

[cjacek]

Yes, it definitely makes sense, what you're saying Otto but at the same time I'm not going after certain values but rather trying to, by ear, match what I'm hearing from source vs off tape. Now, if I, very carefully, patiently, match it all up so that white noise is virtually identical all around (off tape matches source) then have I not, in turn, calibrated the recorder to put out what it is being fed in, as far as a variety of musical material, real world result? Doesn't white noise more or less represent complex sounds, what one would find on a variety of recordings? If I can match it all up (with white noise), then anything should sound properly on playback. That's at least my line of thinking and I guess I'm trying to open up the possibilities that there's another way of doing this, other than calibrating at certain fixed values. Even if there are dips here or there, on an analyzer or other discrepancies, "on paper", I may not even hear it off tape, especially when it matches source. Do I believe my ears or a piece of test equipment? Again, I'm not trying to force a way on someone or come off as a know-it-all but rather to get some input on this way of doing things.

 

[Tim Gillett]

Do I believe my ears or a piece of test equipment?

Daniel, if the test equipment is used correctly, your ears will appreciate the difference in the better recording. Sure, as a final check, I always used 'my ears' after an alignment because it's just common sense to do so. But my ears were always in agreement with what the test instruments were telling me.

There is no conflict that I know of between test equipment and "our ears".

Cheers Tim

 

[ofajen]

Yes, it definitely makes sense, what you're saying Otto but at the same time I'm not going after certain values but rather trying to, by ear, match what I'm hearing from source vs off tape. Now, if I, very carefully, patiently, match it all up so that white noise is virtually identical all around (off tape matches source) then have I not, in turn, calibrated the recorder to put out what it is being fed in, as far as a variety of musical material, real world result? Doesn't white noise more or less represent complex sounds, what one would find on a variety of recordings? If I can match it all up (with white noise), then anything should sound properly on playback. That's at least my line of thinking and I guess I'm trying to open up the possibilities that there's another way of doing this, other than calibrating at certain fixed values. Even if there are dips here or there, on an analyzer or other discrepancies, "on paper", I may not even hear it off tape, especially when it matches source. Do I believe my ears or a piece of test equipment? Again, I'm not trying to force a way on someone or come off as a know-it-all but rather to get some input on this way of doing things.

I hear what you're saying and I commend you for really thinking about this.. You are correct that if white noise sounds relatively unchanged, then yes, you are probably not too far off, but you could easily have deviations of several dB buried in there that are hard for your brain to unpack when all that comes at you at once. Remember 1 dB is supposed to be the smallest level change you can reliably notice, but with all frequencies present, even larger deviations in a certain band could be hidden by the rest.

By doing precise calibration, you know where you stand all across the spectrum with greater precision and can get the optimal calibration which will do the BEST job of recreating noise or music or whatever.

My point is simply that doing it accurately doesn't take very long and thus is worth doing. There are ways of doing an accurate job that save time, such as using calibration tapes with tone sweeps. Especially for folks with 24 track machines in commercial use where different tape formulations are being used, speed is essential.

Another example is biasing for minimum modulation noise, a method I described in this forum a month or two ago. That's a time-saver for folks with 24 track machines.

With only 8 tracks and using the same tape for a while, I really won't have to do much after I verify the pinch roller pressure, button the beasty back up and then change out the card with the rec level probem.

I'm hoping it'll just need a periodic check to make sure things are still right on and maybe a tiny tweak. That has pretty much been my experience with the 3Ms and I figure Otaris are more stable. Given that, doing the standard procedure is not burdensome and it is the most precise way to calibrate.

Cheers,

Otto

 

[Tim Gillett]

It might help to say that with analog tape recording, there is no one record bias setting that is optimum for all frequencies. If you optimise for the low frequencies, you are overbiasing (actually partially erasing) the highs. If you optimise for the highs you weaken the lows somewhat. A compromise has to be reached.

That's partly why in better machines you can use different bias settings and then tweak the highs in the record amp to help compensate for these different bias settings and keep the response still reasonably flat.

It's possible, within limits, to tweak the bias and rec eq to give better performance in the highs while compromising the lows, or go the other way and get better performance from the lows while trading off a bit in the highs. This is not about frequency response as such but dynamic range and least distortion at a given frequency.

This may seem to be getting a bit fancy for most people but this technique was used to squeeze the most out of analog tape where top performance was required.

So the advice for overbiasing different tape types at 10khz by a certain number of db's was really only a suggestion. You could alter it somewhat if you knew what you were doing.

 

[ofajen]

It might help to say that with analog tape recording, there is no one record bias setting that is optimum for all frequencies. If you optimise for the low frequencies, you are overbiasing (actually partially erasing) the highs. If you optimise for the highs you weaken the lows somewhat. A compromise has to be reached.

Here is a great article by Jay McKnight that explains biasing pretty well:

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

Definitely worth reading if you use tape machines.

Cheers,

Otto

 

[cjacek]

Otto, Tim... Thank you both very much. Point taken. Cheers!