upon a time, three wise men (no, not the ones you’re thinking of; these guys were
from NBC, CBS and AT&T) came to call on John Miller, vice president and chief
engineer of Weston Instruments in New Jersey (which to some may be The Holy Land).
type 30, model 862 vu indicator with ‘B’ scale on RCA OP-6 portable amplifier. A
Daven resistor network reduced the output from +11 dBm to telco-required +8 for
3 dB line isolation, sent the proper voltage to the meter, provided the 3k9 buildout,
and also created an output Z of 150 ohms to improve frequency response on feeding
telco lines. Two No. 47 frosted lamps mounted below the glass illuminated the scale.
There, the trio complained that the “dB” indicator
that all broadcasters had been using had many serious drawbacks, which they went
on to list.
the indicators were designed so that a meter could be used on either 500- or 600-ohm
program lines, which are not the same. It indicated 1.73 V at “0” on the scale on
500-ohm lines (used in motion picture sound recording), but it needed 1.9 V to do
it on 600-ohm broadcast lines.
only was the scale’s range a scant 16 dB, but the zero mark was reached before midpoint
on the scale, thus wasting more than half of the scale area. The meter’s resistance
was so low — 5k-ohms at “0,” dropping to only 1774 ohms at program levels of –9
dB — that it loaded the line it was supposed to bridge.
there was the fact that the pointer moved too fast, indicating peaks that the movie
boys liked for optical recording, but which masked the average program level
monitoring required by broadcasters.
to this was the high contrast of the black-on-white scale, which made for rampant
operator eye fatigue. Not only were the meters frequency-sensitive, they were also
inaccurate at voltages other than whatever was required to move the pointer to “0.”
insult to injury, it took too long for the pointer to settle down to proper power
indication from its overshoot. What a mess!
took on the task of fixing all of this, and lo, 75 years ago the vu indicator came to pass.
I say “indicator” because what we call a “meter” is not one (the indicator of electricity
consumption at our homes is a meter). But with this revolutionary industry standard
came an obligation: You have to hook it up right, or it won’t be accurate.
can’t put “vu” scales on AC voltmeters and expect them to give you indications you
can rely on, nor any other true vu meter’s benefits. You mustn’t use them on lines
other than those with a net impedance of 300 ohms (600-ohm source to 600-ohm load).
are things you don’t know about these indicators:
not in the NSA spec, “vu” should be written in lower-case letters
not mandatory, the “A” scale (vu indications predominant) is only for use on test
equipment and limiters, while the “B” scale (percent modulation indications above
the arc) is for everyday program level monitoring.
why is it that we don’t find meters with “B” scales in any studio today?
blame Ray Dolby for that. You see, in the 1950s, when Dolby designed the circuit
for the early Ampex tape recorders, he knew little about vu meters and broadcast/recording
practices. So he figured that the vu scale (used just when calibrating the recorder)
should be predominant.
that moment on, virtually every broadcast and recording equipment maker (save, perhaps,
RCA, Gates, Collins, Sparta) and recording studio operator (except yours truly)
repeated Ray’s mistake.
referred to dB meters as power indicators (6 mW power at “0”) and to vu meters as
“volume” indicators. But as volume is construed to denote power, vu
meters will indicate 1 mW at 0.7746v when the pointer is at –4 vu, and 1.228v
when the pointer is at “0” (100% on the percent modulation scale).
scale indicates percent power and percent voltage; ideal for studio and transmitter
use. What’s a volume unit? It’s numerically equal to the number of decibels
above or below 1 mW. Thus the term “volume unit” (coined by Miller) can’t apply
to a dB meter designed for 6 mW lines, nor can it apply to any pseudo vu meter.
of Miller’s new design, based upon a DC microammeter with a carefully selected rectifier
(probably made by Conant) was the 1938 introduction of this radically different
volume level indicator, which has stood the test of time under its “street” name:
one beautiful meter!
see how carefully it was crafted. You’ll see that it’s truly ingenious.
an impedance of 3k9 ohms when a 1 kHz signal pushes the pointer to “0” (4 dB
above 1 mW). But it must be used with a 3k6 resistor in series. While reducing line
loading, this minimizes the unavoidable impedance change with signals other than
1 kHz and 1.228 volts.
a major characteristic that makes the meter the gem that it is: It must see its own impedance. Is
a 3k9 instrument seeing its own impedance via the 3k6 buildout resistor? Of course
not. Yet don’t forget the 300 ohm (600/600) program line, which added to 3k6 gives
3k9, matching the meter’s 3k9. QED.
bear in mind that without this impedance matching, the meter will not be accurate.
Even a real, standard vu meter will not be accurate without matching.
else did Miller do for the radio guys? He damped the meter so as to minimize overshoot
(the purpose of damping), which also slowed the pointer action so that the meter
reads average program levels not masked by occasional peaks.
point on the scale is far right of center, permitting maximum scale utilization,
and its range was increased to 23 dB. He further improved legibility and reduced
eye fatigue by specifying a buff color (yes, it’s in the spec), and by creating
a scale where overvoltage readings are in red.
benefit is that the meter and build-out resistor, totaling 7k5 ohms, met the desired
12.5 times the program line’s impedance for minimum line loading. Myriad parameters
had come together in a perfect fit. Many meter makers began offering vu meters after
the advent of Weston’s Type 30 series.
of these companies, including Weston, no longer exist. What came closest to Weston’s
in styling was made by Simpson. Other meter makers were Assembly Products, Burlington,
Marion, Dayton, Beede, Hoyt, Selco, Modutec (though the Triplett’s I tested didn’t
dealer merits a mention. It’s Metercraft of Santee, Calif. Not only are they dealers,
but they did a marvelous job salvaging the “irreparable” Weston pictured here. Applause!
to add a vu meter to your mixer? Easy. Terminate that lo-Z unbalanced output with
a 300-ohm resistor. Then place a standard meter having a 3k6-ohm resistor in series
with it across the 300-ohm resistor and voila! You’ve done it. Your volume
indicating will be accurate, easy on the eyes and legible.
relying on flashing lights. You’ll now have a traditional broadcast-standard zero-level-line.
And don’t forget what the manufacturers don’t tell you: Only a factory-adjusted
meter can be used on steel panels or within two inches of a ferrous metal.
don’t expect a meter with an expanded scale to be a true vu meter unless all specs
have been met and practices adhered to.
unfortunate aspect of the vu meter, which didn’t matter at the time and rarely does
today, is that the meter’s frequency response rolled off at 10 kHz. At the request
of a major recording studio products maker, I recently tested a Chinese vu meter
he’d been using in a limiter. It flunked all tests save one: It was flat to
“uses and abuses of the vu meter” story happened many years ago. A famous beauty
products maker, Charles Antell Co., bombarded national audiences with a TV commercial
for a new shampoo. We saw a woman’s head, above which was her hairdresser’s arm,
holding a light meter to prove how bright the lady’s hair became after a Charles
a note to The Hollywood Reporter, advising gossip columnist Mike Connolly about
this sham. Connolly soon wrote, “Oliver Berliner says the light meter used in the
Charles Antell commercial is actually a Simpson model 142 vu meter.”
Antell quickly pulled the spot.
Berliner is a self-styled leading authority on uses and abuses of the vu meter.
Reach him at email@example.com.Comment on this
or any story. Write to firstname.lastname@example.org.