Maintaining Audio Quality in the Broadcast Facility 2011 - Orban

30
Maintaining Audio Quality
Where the average energy level of a signal varies with time, the louder moments
contribute most to our perception of overall loudness. For example, in human
speech, over half the time is silence, but this does not affect the perceived loudness
of the talker at all! For this reason, the RMS values are sorted into numerical order,
and the value 5% down the list is chosen to represent the overall perceived loudness
of the signal.
4. Calibration with reference level
A suitable average replay level is 83dB SPL. A calibration relating the energy of a
digital signal to the real world replay level has been defined by the SMPTE. Using
this calibration, we subtract the current signal from the desired (calibrated) level to
give the difference. We store this difference in the audio file.
5. Replay Gain
The calibration level of 83dB can be added to the difference from the previous calculation,
to yield the actual Replay Gain. NOTE: we store the differential, NOT the
actual Replay Gain.
Speech/Music Balance
The VU meter is very deceptive when indicating the balance between speech and
music. The most artistically pleasing balance between speech and music is usually
achieved when speech is peaked 4–6dB lower than music on the console VU meter. If
heavy processing is used, the difference between the speech and music levels may
have to be increased. Following this practice will also help reduce the possibility of
clipping speech, which is much more sensitive to clipping distortion than is most music.
If a PPM is used, speech and music should be peaked at roughly the same level.
However, please note that what constitutes a correct “artistic balance” is highly subjective,
and different listeners may disagree strongly. Each broadcasting organization
has its own guidelines for operational practice in this area. So the suggestions
above are exactly that: just suggestions.
For a given VU or PPM indication, the loudness of different talkers and different
music may vary significantly. A short-term loudness meter like the Jones & Torick
meter can help operators maintain appropriate voice/music balance by estimating
more accurately than a PPM or VU the actual loudness of each program segment.
Many of Orban’s Optimod audio processors have automatic speech/music detection
and can automatically change processing parameters for speech and music. Setting
these parameters to achieve your organization’s desired speech/music balance provides
an effective way of controlling this balance automatically.