Transform Function Of Drc System In Ac-3, Aacplus, And Others - Linear Acoustic MetaMAXLA-5180 Operation Manual

Linear Acoustic LA-5180 Metadata Frame Sync/Generator Operation Manual Metadata
RF Mode is designed for products (such as set-top boxes) that generate a downmixed sig-
nal for connection to the RF/Antenna input of a television set; however, it is also useful
in situations where heavy DRC is required-for example, when small PC speakers are used
for DVD playback. In RF Mode, the overall program level is raised 11 dB, while the peaks
are limited to prevent signal overload in the D/A converter. By limiting headroom, severe
overmodulation of television receivers is prevented. The 11 dB gain provides an RF mod-
ulation level that compares well with analog television broadcasts and premium movie
channels.
In some situations it may be necessary to further constrain signal peaks above the average
dialogue level so that there is less than 20 dB of headroom. The selection of a suitable RF
Mode profile achieves this.
Dynamic Range Control Profiles
Six preset DRC profiles are available to content producers: Film Light, Film Standard, Mu-
sic Light, Music Standard, Speech, and None. Each is generated based on the transform
function shown below. As DRC is a wide-band gain control, all DRC profiles are generated
using a modified B-weighted curve to prevent intermodulation.
Figure 7-1 Transform function of DRC system in AC-3, aacPlus, and others.
In each case the center of the null band is assigned to the dialogue level parameter setting,
and the DRC profile is applied in relation to that level.
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