About Transmission Levels and Metering
Meters
Studio engineers and transmission engineers consider audio levels and their measurements
differently, so they typically use different methods of metering to monitor these levels.
The VU meter is an average-responding meter (measuring the approximate RMS level) with
a 300ms rise time and decay time; the VU indication usually under-indicates the true peak
level by 8 to 14dB.
The Peak Program Meter (PPM) indicates a level between RMS and the actual peak. The
PPM has an attack time of 10ms, slow enough to cause the meter to ignore narrow peaks
and under-indicate the true peak level by 5dB or more.
The absolute peak-sensing meter or LED indicator shows the true peak level. It has an
instantaneous attack time, and a release time slow enough to allow the engineer to easily
read the peak level.
Figure 1-1 shows the relative difference between the absolute peak level, and the indications
of a VU meter and a PPM.
For a Few Seconds of Music Program
ABSOLUTE PEAK
PPM
VU
Figure 1-1: Absolute Peak Level, VU and PPM Reading
OPTIMOD-FM 8200
INTRODUCTION
1-17
