Handbook for Sound Engineers

VI Meters and Devices 1005

meter also includes peak memory, peak hold, +40 dB

gain, and a three-color correlation correction value

display.

The RTW 11528G AES/EBU Digital PPM, Fig.

26-11B is especially useful for radio and TV broad-

casting applications. The meter features AES/EBU

inputs and outputs. The digital signal can be displayed

once as it is without any weighting (sample precise

display), which corresponds to the digital standard that

has a scale range from –60 dB to +9 dB but with a fixed

head room of –9 dB FS, which is marked 0 dB, and

highlighted and superimposed with an integration time

of 10 ms. It can also be displayed with a superimposed

and highlighted loudness display. Finally, it can be

shown as a 10 ms integration time–only function, as a

quasi analog display. Its sampling rates are from 27 kHz

to 96 kHz.

Both the RTW 11529G and the 11528G include an

over indication with a selectable overload detector

range, 9 to 24 bit overload response word length, and

number of overload samples.

26.9 Loudness Meters

Loudness meters place VU and PPM meters on a single

panel, providing an indication of the entire dynamic

condition of the signal. It also eliminates the condition

that eyeball wobble could develop in the attempt to

follow two adjacent meters with differing ballistics. The

use of two pointers with such differing ballistics on a

single scale would demonstrate that the PPM would

read consistently higher levels than the VU meter, and

the large differential of decay with respect to rise time

of the PPM in comparison to the equal rise and decay

times of the VU meter would also be difficult to

interpret.

Three types of scales are used on loudness meters:

• Based on +14 dB of headroom.


• Referenced at 100% for broadcast transmission.


• Based on 20 dB of headroom.

The head room available to mixers in postproduction
is not the same as allowed in broadcast. The U.S. stan-
dard in digital (SMPTE) is 20 dB below FS (full scale)
and the EBU standard used in European and many
Middle Eastern countries is 18 dB below FS. When
film and post material is sent to the broadcast facility,
the peak shall not exceed +12 dB analog or 8dB
digital.
The music and recording industries do not have these
requirements for their products, and therefore use the

full dynamic range. Commonly, this material will peak

fairly consistently at 1 dB on a digital reading meter,

with the bar graph fairly consistently four or five LEDs

under the peak. If this material makes its way to broad-

cast, it will be louder than audio on video by possibly as

much as 8 dB. The result might be rejection and need to

redo the material using the guidelines required, or

quality control at the broadcast facility will make a

judgement on the loudness and turn it down accord-

ingly. Dialnorm on HDTV was designed for these irreg-

ularities.

Observation of complex audio signals with an oscil-

loscope indicates the peak excursions of the program

material. The use of an oscilloscope with a long or vari-

able persistence CRT will show additional information

relative to recurrent amplitude displayed by the persis-

tence of the screen as a concentrated band of energy

about the center of the CRT. It is these two pieces of

information that provide the composition of acoustically

related peak to quasi-average information. The meters

shown in Fig. 26-11 feature a loudness display and peak

holding display on each bargraph.

The meter in Fig. 26-12A is an analog reading meter,

a digital reading meter is shown in Fig. 26-12B, and a

remote control unit to access features from both is

shown in Fig. 26-12C. The remote pushbuttons control

the following functions:

• Left/Right.


• Sum/Difference.
  •Phase.


• Overs Display with Overs Reset.


• Three second Peak Hold.


• Peak Hold Permanent.


• Reference Mode.

Figure 26-11. An AES/EBU peak program meter plus loud-

ness meter plus phase correlation meter. Courtesy RTW

GmbH & Co.KG, Cologne.

A. RTW 11529G Digital Peak Program Meter +

Loudness Meter + Phase Correlation Meter.

B. RTW 11528G Digital Peak Program Meter +

Loudness Meter + Phase Correlation Meter.