Handbook for Sound Engineers

VI Meters and Devices 1003

programmable character generators. This eliminates any

need for screen overlays or masks and ensures accurate

positioning of the alphanumeric information regardless

of screen size or width and height adjustments.

Some typical displays are:

• 6 or 32 simultaneous VU channels.


• 16 or 2 × 16 bands of frequency spectrum (1 or 2
  channels).


• 16 VU channels, plus channels of automation control
  voltages.


• 16 VU channels, plus 15 bands of frequency spec-
  trum and 1 composite level.

One VU module provides 16 bar graphs with stan-

dard VU ballistics over a display range of 30 dB. Each

bar has two shades of gray, with the lighter shade above

the 0 dB reference. When a signal is applied to any of

the 16 inputs, a bright bar moves up and down with the

signal level. The 0 dB reference point can be continu-

ously adjusted to any standard from 0 to +8 dB. The VU

module is user programmable to display a logarithmic

scale of 20 dB to +3 dB when measuring audio signals

or to read linearly from 0 to 10 for display of ac or auto-

mation dc control voltages.

The spectrum module provides a visual real-time

display of VU level versus frequency of an audio signal.

It is useful for setting equalization and adjusting

frequency balance. This module provides 16 bar graphs

with visual characteristics similar to those of the VU

module. One bar is assigned to the full spectrum of the

audio signal, and the other 15 channels display incre-

ments of the frequency spectrum, centered on standard

ISO -octave filter frequencies. Two independent

controls adjust the level of the full spectrum bar relative

to the spectrum analysis bars.

26.5 Power-Level Meters

A power-level meter is a VI meter calibrated in deci-

bels. As a rule, this type of meter is normally used with

test equipment for steady-state measurements and is not

used for monitoring program material because its ballis-

tics are more like those of a voltmeter.

26.6 Power-Output Meters

A power-output meter is used for measuring the power

output of audio amplifiers and other devices. It may also

be used to determine the characteristic and internal

output impedance, the effect of load-impedance varia-

tion, and other applications involving the measurement

of output power and impedance with respect to

frequency. The power output meter may be calibrated in

watts and/or dBm. The power output meter is a test

instrument and not used for monitoring program level

because of its ballistics.

26.7 Peak Program Meters

The peak program meter (PPM) is used extensively in

Europe and falls under four standards, the DIN-type

DIN 45406, the BBC type, the EBU type, and the

Nordic N9 type. These meters measure the peak

program signal, which is usually +6 dB to +20 dB

above the readings seen on the VU meter.

26.7.1 DIN 45406 Standard

The PPM is popular in Europe. It is designed to have a

fast rise time, 30 times as fast as a VU meter, and a

much slower fallback or decay time.

Figure 26-8. Wide range VU meter. Courtesy Dorrough Electronics.

Figure 26-9. Block diagram of a wide-range program
monitor VU meter.

Bridging

input

Reference

level selector

Preamplifier

Operational

amplifier

Rectifier

Nonlinear

feedback

Meter

dc output^2 »^3