Handbook for Sound Engineers

1006 Chapter 26

The alarms on the left side of the remote are for
Phase Error, Bit Stream Corruption, and Full Scale. Fig.
26-13 is a block diagram of the loudness meter of
Fig. 26-12.

With signal input both meters read the audio in the
same dynamic way. Each meter displays 20 dB of Peak
Amplitude above the 0 VU persistence reference level,
and therefore, 0 reference is the same on both.

The use of a dot display for Peak information and a
bar display for Persistence information allows a single
display for both ballistics. Each lamp in the display is
therefore driven by two drivers, one for peak, the other
for persistence. This representation presents a display of
a dot riding on top of a bar graph. In order to make this
display useful, there has to be a meaningful relationship
between the two ballistics. The peak display has a rise
time of two time constants, or 10μs, which is 1000

times faster than the PPM. The decay time for the peak

display is 18 ms/dB.

Equal energy, properly weighted for program mate-

rial, will be discerned as equal in loudness. Since energy

can be displayed as a function of amplitude and time, an

oscilloscope can be used to confirm that large ampli-

tudes of short tone bursts can be equal to longer tone

bursts of lower amplitude.

Average power is defined as equal to the area under

the curve divided by the time interval. Since the area is

equal to the input energy, W or watts, during the

interval,

(26-7)

where,

W is in watts,

t is in seconds.

Thus, the averaging-type metering can provide an indi-

cation of power.

The persistence display has a time constant of

270 ms and a rise time of approximately 600 ms or

twice as long as that of a VU meter.

Perceived loudness to the ear from source to source

is determined by which circuit (peak or persistence) is

first to illuminate its respective set of red LEDs.

Program adjustments for equally perceived loudness

should be holding either the peak or persistence excur-

sions to its corresponding red LED area.

The relative loudness characteristic of the Peak to

the bar graph has been retained by way of red LED

reference points on both meters. This is the window of

12 dB of separation of the Peak from the Average for

maintaining equal loudness. The +12 dB analog and

8 dB digital are the same scale points on both meters.

26.10 Surround Sound Analyzer

The surround sound analyzer method translates the

important details of surround signals into a graphical

display suited for instant evaluation. Successful mixing

of surround signals is important. Besides the artistic and

aesthetical aspects, there are fundamental technical

preconditions for obtaining professional results.

Reality is often far from the ideal, particularly during

live broadcasts and in audio production for video or TV.

This makes it even more important to know, even in the

most hectic working environment, how the surround

mix will be perceived by the listener.

The RTW Surround Sound Analyzer—e. g., inte-

grated in the RTW SurroundMonitor, Fig. 26-14—is a

Figure 26-12. .The meter scale for a gain-riding device with
both a normal persistence range (much like VU readings)
and a normal peak range. Courtesy Dorrough Electronics.

A. Analog reading B. Digital reading

C. Remote control

Pave W

t

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