Dolby Laboratories DP564 - Manual (Page 77)

DP564 Multichannel Audio Decoder Appendix A: Metadata
A-7
Note: While the use of DRC modes during decoding is a consumer-selectable
feature, the dialogue level parameter setting is not. Therefore, the proper
setting of the dialogue level parameter is essential before previewing a DRC
profile.
Line Mode
Line Mode offers these features:
• Low-level boost compression scaling is allowed.
• High-level cut compression scaling is allowed when not downmixing.
• Dialogue, as set by the dialogue level parameter, is reproduced at a constant
level of –31 dBFS LeqA.
All line-level or power-amplified outputs from two-channel set-top decoders, two-
channel digital televisions, 5.1-channel digital televisions, Dolby Digital A/V
surround decoders, and outboard Dolby Digital adapters use Line mode.
Consumer control of the dynamic range is limited when downmixing. Products with
stereo or mono outputs do not usually allow consumer scaling of Line Mode. This is
because these devices are usually downmixing, (for example, when receiving a
5.1-channel signal.) However, in these products the consumer may have a choice
between Line Mode and RF Mode.
RF Mode
RF Mode offers these features:
• High- and low-level compression scaling is not allowed
(when active, always fully applied).
• +11 dB gain shift raises overall program level.
• Dialogue, as set by the dialogue level parameter and combined with the
+11 dB gain shift, is reproduced at a constant level of –20 dBFS LeqA.
RF Mode is designed for products (such as set-top boxes) that generate a downmixed
signal 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 modulation 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 headroom. The selection of a
suitable RF Mode profile achieves this.