How do you find VU meter specs?

[ihscoutlvr74]

I have several VU meters but don't know their specs. How does one determine the ma, etc. Have some meters from Ampex 354, some Roberts/Akai, some Altec meters.

I'm much appreciate any info on this probably simple testing.

Thanks, Nathan

 

[SSLtech]

You don't 'measure' the specs as such: the VU meter IS a specification, so if a meter is a VU, it has to meet spec.

The test for determining if something is a standard-spec VU meter is a 3.9k external series resistance, with a +4dbU AC signal applied across the chain.

If it goes to 0VU, it's a VU meter.

Some draw less current, others more, but if the required external resistance is anything other than 3.9kΩ, they invariably mark it on the meter.

This is all searchable, but I thought I'd give a short reply to cover this particular aspect.

Keith

 

[Ptownkid]

That's actually really helpful, been trying to wrap my head round this one lately, but the online info is often written for people who already get it...

 

[SSLtech]

:green:

True...

once you have the above info, if you go and look at an LA-2a meter switching and an 1176 meter switching schematic, it starts to make perfect sense. -Ignore the gain reduction indication, just look at how they simply wire the meter across the output, with a couple of options for series resistance to produce more or less meter sensitivity...

Bingo!

Keith

 

[radiance]

Some more info I found use full...

http://www.jlmaudio.com/AT51%20DIY%20VU.pdf

 

[JohnRoberts]

dBu....

BTW "True" VU meters also have a defined ballistic or response to transients and step functions.

Back in the day before inexpensive peak meters, experienced recording engineers learned how to apply windage for different instruments to get repeatable results when tracking with standard VU meters. If the meter ballistics varied from standard they would be worthless.

Any meter with a VU legend can be calibrated to line up with a steady tone at 0VU, but may not deliver the true VU response for dynamic signal. Since the vast majority of VU meters these days are used for retro cosmetics or fashion more than utility, the cost of real "true" VU meters is probably not justified. They were expensive back then as I recall.

JR


Edit: this is all described in more detail in JLM link posted by radiance.

 

[SSLtech]

dBu.. not dBU... quite right, -my shift key was a bit slow coming off! :grin:

Yes, this is all falling under the 'searchable' stuff...

The trouble when people say "VU Meter" is that it's almost become accepted as the generic term for any sort of moving coil meter. -Don't believe me? -search eBay, and you'll see plenty of misuses of the term.

Even some cassette decks had moving coil meters on them, which were actually DC meters, but the scale said "VU". They were driven by an external DC meter driver circuit, but you can't use them as regular VUs.

Unless you've got some specific optical set up on your lab bench to measure attack time, overshoot, hysteresis and probably a few other things, you won't be able to tell if they meet Vu spec.

In fact the oft-bought and sold Sifam 'AL-xx' series do NOT meet full VU spec. Theyr'e pretty close, but they are sold by Sifam as "Audio Level meters" (hence the "AL" deignation) and never referred to as VU meters in the Sifam literature. -That's because Sifam are scurulously accurate in their description. -Beede however, claim that some of their meters are VU meters, when the scaling linearity is out by more than a dB!!! (Set signal for 0VU, reduce signal by 3dB, Beede VU reads -4.1dB... that's not just a little bit off, that's pretty heinous by ANYBODY'S standards!)... And they have no problem describing that as a spec-meeting VU meter.

The finest meters which I have are the Sifam 'Clarity' series, and I use it as a performance benchmark for 'eyeball' comparisons for overshoot, rise time etc. I also have some Shinohara meters (some good, some B-A-D!) a few APIs, some Componex, Beede, Calrad, Modutec and who knows what other brands here.

My initial answer was a reduced simplified test to eliminate meters which will NEVER be VU meters... nor can they ever be. It was not intended to be a description or definitive full VU spec. acceptance testing, since non-loading ballistic measurements needs optical gear, timing equipment and some means of connecting or synchronizing them...

It does indeed seem like there's NEVER any way to answer this question simply, even though the original poster -just like everyone else who's ever asked- seems to think that it's a simple matter...

I'm much appreciate any info on this probably simple testing.

..Maybe next time I should just go with my knee-jerk reply, which is something along the lines of "Run a search, you moron!!!" :wink:

Keith

 

[JohnRoberts]

I consider this discussion an opportunity to put VU in historical perspective. Back in the day "precision" was what made VU an effective tool for monitoring levels.

FWIW VU (volume units) are conveniently exactly 1 dB wide. 0VU as a reference level is a long story indeed, and the link earlier in the thread gives it a good start.

Ask any recording engineer from the days of VU and magnetic tape, and they'll recite their offset list for what VU level to track different instruments at to prevent tape saturation (from peaks).

JR

 

[SSLtech]

VU meters have their place still, as RMS power indicators referenced to a nominal point. For loudspeakers for example, peak is often less absolutely destructive than RMS (heating power).

For digital recording however, the letters VU no longer represent "Volume Units", instead they transmogrify to mean "Virtually Useless".

Our second SSL console (22 years ago) was ordered with BBC-scale PPM metering (sifam, of course) and the Otari machines were in line-of-sight, so we were able to visually observe BOTH at once. -I adored it, but visiting engineers were more dismissive...

Keith

 

[ihscoutlvr74]

THanks for the overview and advice, gents!

 

[David Kulka]

I disagree with Keith a bit here (a rare event) and feel that VU meters are still very useful and valuable.

I was helping a client check the matching of the line input levels on his new analog desk. Would have been great if the new expensive mixer had VU meters, but it did not. The built in very coarse LED meters were quite useless. We patched the desk outs to an 1176LN and calibrated it for +4. (VU meters have outstanding resolution.) That done, it was easy to check levels.

Maybe it's the old guy in me talking but I still feel that good meters are best for giving a sense of actual loudness. Peak meters and LED's tell you how much headroom is left but may not convey the apparent loudness of a sound.

 

[radiance]

Found these on evilbay...It sais VU on the scale. If they're really VU I think it's a bargain. Any thought?

http://cgi.ebay.de/A-Nice-Pair-Sifam-VU-Meters-1mA-England-metre-NOS-meter_W0QQitemZ120229603540QQihZ002QQcategoryZ67812QQcmdZViewItemQQ_trksidZp1742.m153.l1262

 

[Ptownkid]

The sifam directors are true vus tmk.

 

[radiance]

[quote author="Ptownkid"] true vus tmk.[/quote]

What's that? VUS TMK?

 

[Ptownkid]

Vu meters...to my knowledge

 

[radiance]

AFAIK, "Director" is just the name of the housing of this meter. The Director used in the ssl for example is a PPM meter, not a VU. The Director might come as VU, like I hope the ones in the ebay ad are.... :grin:

 

[Ptownkid]

Yeah, you're right, after looking at their site, I have no idea how to tell what is what...the directors come in both Vu and ppm (with respect to their audio versions) and have the same size codes...so no info there.

 

[SSLtech]

They make Director, presentor, clarity etc... the best ones I've ever seen are 'Clarity' VU.

 

[JohnRoberts]

[quote author="David Kulka"]I disagree with Keith a bit here (a rare event) and feel that VU meters are still very useful and valuable.

I was helping a client check the matching of the line input levels on his new analog desk. Would have been great if the new expensive mixer had VU meters, but it did not. The built in very coarse LED meters were quite useless. We patched the desk outs to an 1176LN and calibrated it for +4. (VU meters have outstanding resolution.) That done, it was easy to check levels.

Maybe it's the old guy in me talking but I still feel that good meters are best for giving a sense of actual loudness. Peak meters and LED's tell you how much headroom is left but may not convey the apparent loudness of a sound.[/quote]

Since I was dumping on VU more than Keith, I'll respond.

Yes, analog meters have more resolution around zero. This is a constant complaint with LED meters. I'll add another, if a bank of LED meters don't all light at exactly the same voltage customers think something is wrong, but they never complain about VU meters being a fraction of a dB off, due to calibration or whatever (perhaps not the meter but as used).

Indeed VU (ave) is more representative of loudness than peak. This is useful when mixing to gauge relative mix volume or channel contributions, while presumably you have ears to make final decisions in that regard.

I'm a win-win kind of guy so I like to give mixers both. Back when I was putting VU meters in consoles I also put a peak LED right next to them to indicate headroom status since you could clip a console and never see it in VU meters. I consider combination peak/VU meters a best of both worlds as you get all the information of both types and some extra information from the concurrent presentation.

The line up resolution is a separate issue from normal use. With audio you are lucky to parse out level differences that small. I suspect "line up" could be better managed in LED meters with a PFL mode or something like that.

I've always found more than two mechanical VU meters in a row, or rows, hard to scan for practical information (an acquired skill?). I'll take a meter bridge with 40 LED bars over 40 VU meters any day (but I'm biased). YMMV.

JR

 

[SSLtech]

Ah, well tomorrow evening I'm going to do battle with an old 200-segment Plasma-bargraph E-series which has burned/fried/smoked most of its ring drivers... At times like that, I LONG for mechanical VU meters! :green:

yes, I really was being a little flippant, and my only real point in making that jab was that VUs dont tell you squat about clipping, and when recording digitally, the avoidance of clipping is so often the most important consideration.

However, the resolution of 200-plus segment bargraphs is pretty good... equivalent down to a needle's width or so in moving coil terms. -However, I curse the reliability of the SSL plasma bargraph design to the very bowels of hades. -Neve did a MUCH more reliable job on their V-series, but then they went and buggered up the entire thing, by making repair access infuriatingly complicated for when the "three-legged silicon fuses" (MPSA42 and MPSA92) need replacement.

I do indeed like a nice VU meter, and I have a wonderful collection here. -but when high-resolution bargraphs are working properly, they are a thing of beauty.

Mind you, even the Triplett VUs which I have have a nasty hysteresis (bearing friction, I assume) which makes them a little sneakily suspect for doint small tweaks with a constant tone...

But I do love the Sifam Claritys... (which are the type that SSL use).

Keith