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Compellor
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outputs into the codec, the level will then shift and be louder with the analog input. That may
give the effect of a fuller on-air sound when the coder is driven by analog because the on-air
audio processor at the decoder side is driven with higher input level.
What, Me Worry?
This level mismatch need not be a problem, especially if you intend to use only the digital out-
put. Simply readjust the final audio processor to be optimal with the –20dBFS average digital
audio input level. If you want to also use the Compellor’s analog output for comparison or for
a backup plan, then you can readjust the coder’s analog input gain, if available, or add an
external attenuator to the coder’s analog input to get the –20dBFS digital reference conver-
sion. Reducing the Compellor’s analog output gain will not solve the problem because
it will also drop the digital level proportionately.
Summary
Increasingly, audio monitoring is a mixed bag. Some equipment with VU, some with PPM and
some with dBFS. Only if you understand what the meters show, will you be able to use them
properly. Being aware that VU meters indicate relative volume level without regard to peaks
and that PPM or dBFS peak meters indicate the available headroom below clipping without
regard to perceived loudness is most important. Secondly, it is important to know how to set
up an operating level. With these two bits of knowledge, you will be able to find a satisfactory
solution to all of your audio interfacing problems. Confusion: Gone!