Table of Contents
Advertisement
OPTIMOD-PC
being more powerful than its competition. We expect that the same subliminal psy-
chology will hold in netcasting too.
Figure 1-1 shows a 15-minute snapshot of program audio as it emerged from the on-
air mixer of a major Los Angeles radio station. Source material included music,
speech, and commercials. Notice the large inconsistency in peak and average level
between one program source and the next. Figure 1-2 shows the same material af-
ter being processed through OPTIMOD-PC, using the G
gram levels are now consistent from source to source
Audio Processing for Netcasts
Professional-grade netcasting requires audio processing similar to FM broadcast (al-
though there are some important differences in the peak limiting because of the
different characteristics of the pre-emphasized FM channel and the perceptually
coded netcasting channel). Your listeners deserve to get the best quality and consis-
tency you can provide. Good audio processing is one important thing that separates
the amateur from the professional.
Conventional AM, FM, or TV audio processors that employ pre-emphasis/de-
emphasis and/or clipping peak limiters do not work well with perceptual audio cod-
ers such as Orban's Opticodec-PC® MPEG4 AAC/aacPlusV2 streaming encoder. The
pre-emphasis/de-emphasis limiting in these processors unnecessarily limits high fre-
quency headroom. Further, their clipping limiters create high frequency compo-
nents—distortion—that the perceptual audio coders would otherwise not encode.
None of these devices has the full set of audio and control features found in Opti-
mod-PC.
Peak clipping sounds bad even in uncompressed digital channels because these
channels do not rely on pre-emphasis/de-emphasis to reduce audible distortion. In-
stead of peak clipping, OPTIMOD-PC uses look-ahead limiting to protect the follow-
ing channel from peak overload.
Measuring Studio and Transmission Levels
Figure 1-3: Absolute Peak Level, VU and PPM Reading
Studio equipment (like mixers) and transmission equipment (like codecs) typically
use different methods of metering to display audio levels. The VU meter is an aver-
preset. Notice that pro-
REGG
ABSOLUTE PEAK
PPM
VU
1-3
INTRODUCTION
Advertisement
Table of Contents
