Page 37
room above the maximum PPM indication. By controlling the audio levels to maintain good
PPM readings, there can be no possibility of the electronics clipping the audio. The disad-
vantage is that to maintain a good average volume level, it takes very clever people riding
the gain who can accurately guess at the crest factor of all the sounds. The BBC of the U.K.
has actually created standards on where to allow music, voices, and commercials to peak on
their own version of a PPM. It just seems so ridiculous when you consider they could all just
adopt the American VU standard.
The VU Standard
Throughout the United States and its sphere of influence in the world is traditionally found the
VU meter as specified by the ASA (American Standards Association, now extinct). The name
VU comes from “Volume Units”. It is the intent of VU meters to indicate the audio level as we
hear it. It does not indicate the peak levels of the audio.
In VU meter practice, audio electronics must be designed to have sufficient peak headroom to
allow safe passage of all unseen audio peaks. To allow this, at least 20dB of headroom above
the 0VU reference level is designed into professional equipment. However, the advantage is
that monitoring and controlling levels by VU indications yields pleasing consistency of sound
levels without any guessing about the crest factor.
0
1
3
5
7
10
20
1
2
3
+
VU
dBFS DIN PPM
dB Full Scale
0
1
3
5
7
10
20
1
2
3
+
VU
-20
-4
-20
-27
-27
8
+5
0
-10
-20
-30
-40
-50
-5
0
-3
-6
-9
-12
-15
-18
-21
-24
-27
-30
-33
-36
-39
dBFS DIN PPM
+5
0
-10
-20
-30
-40
-50
-5
0
-3
-6
-9
-12
-15
-18
-21
-24
-27
-30
-33
-36
-39
Appendix F