The author is a
retired broadcast engineer in Mount Vernon, Va.
This is in reference
to the interesting and informative article in the May 8 issue by
Oliver Berliner (“The ‘vu’
Meter Legacy Shines On”). The author gives the history of
the original meter movement, the impedance matching of the meter
circuitry, and voltage calibration for the classic volume unit meter
and the original instrument designer.
However, I was
surprised that he made no reference to the seminal document, “A New
Standard Volume Indicator and Reference Level,” published in the
January 1940 issue (Volume 38, Number 1) of the Proceedings of the
This 16-1/2 page
document by Chin, Gannett and Morris details the previous audio
signal level measuring devices, the need for a new standard meter to
be used for audio program distribution, desired meter
characteristics, the evaluation and testing methods used on existing
and the proposed new instrument and, finally, the electrical and
mechanical specifications of what we know as the reference vu meter
Berliner indicates that the frequency response of the vu meter he
describes rolls off at 10 kHz, the IRE document states that response
is not to depart from that at 1000 Hz, by more that 0.5 dB between 25
and 16,000 Hz, with no range limit given. My meters extend well
beyond that range.
As pointed out, the
standard includes even the exact color for the dial. And the design
of the spade at the end of the pointer was based on user preference
responses. Dynamic characteristics required that the meter pointer
rise to the 99 percent within 0.3 seconds and then overshoot to
between 101 percent and 101.5 percent, when a continuous 1000 Hz
signal was applied of such RMS voltage to give a 100 percent or 0 vu
The pointer decay
time when such a tone signal is removed is not specified. The 100
percent or 0 vu point is to be at 71 percent of the scale length.
The letters vu or VU
are not printed on meter dial face shown in the IRE document, nor are
they on the Weston instrument. However, Simpson did print upper case
“VU” above the scale ends on its similar-styled meter.
The meters shown on
a mixing console advertisement in one of your sister publications had
meters with “VU” printed on the dials and pointers with straight
ends without the spade design. One would wonder if these meters would
meet the very specific required rise time, overshoot and the damping
of the reference vu meter.
One of the major
considerations in the reference meter was to have a passive
instrument that did not require an amplifier or external power
supply, but which would have a negligible effect on the circuit being
The meter was not to
cause more than 0.2 percent harmonic distortion of the signal within
the circuit being bridged. Having installed many Weston and Simpson
meters together with the specially designed matching Daven brand step
variable attenuator, I have kept a copy of the original IRE document
handy for reference.
I highly recommend
anyone having an interest in the full history of the development of
vu meter to obtain a copy. One source is the AES URL