Dolby E Multichannel Distribution System User Manual | DP571 Dolby E Encoder |
| |
| |
Bit Depth
Version 1.05 and later of the DP571/572 can encode/decode both 16- and 20-bit Dolby E bitstreams. Versions prior to 1.05 offer only 20-bit operation and future versions will offer 24-bit operation. The 16-bit feature allows Dolby E to be used with 16-bit recording devices.
The DP572 automatically responds to the encoded input signal’s bit depth and inaudibly switches to decode the correct Dolby E stream. The bit depth of the current input stream is denoted by the Input Data LEDs.
Note: This only affects the space the Dolby E bitstream occupies in the main AES output and not the resolution of the encoded or decoded PCM audio.
A16-bit/48 kHz AES channel has a data rate of 1.5 Mbps, which is 400 kbps less than a 20-bit/48 kHz channel. To compensate for this lower data rate and maintain the highest audio quality over the maximum number of encode/decode generations, only six audio channels can be encoded in 16-bit mode. As the decoder automatically switches from 16- to 20-bit decoding in response to the input stream, it seamlessly enables decoding the two additional channels.
Selecting 16-bit mode is possible only if the current Program Config uses no more than six channels. For example, while the 5.1 + 2 Program Config is selected, the 16-bit mode is not visible and cannot be selected. Change the Program Config to anything with six channels or less and 16-bit mode can be selected. When 16-bit mode is selected, Program Configs with more than six channels are not available nor are they displayed in the Program Config menu.
Current postproduction practice stores Dolby E in the 20-bit format for both High Definition (HD) and Standard Definition (SD) programming. This allows storing a 5.1- channel mix along with a two-channel foreign language version of the same program on one AES pair of channels on a VTR (usually channels 3 and 4). Channels 1 and 2 normally carry a Dolby Surround or stereo version of the same program. This convention makes the tape useful when the multichannel version is not required or cannot be decoded.
When recording Dolby E onto a digital VTR, certain parameters must be adjusted to identify the signal as data instead of audio. Both the Sony HDCAM and Panasonic HD- D5 have menu settings that switch the audio tracks to DATA MODE. The Sony Digital Betacam is automatically in DATA MODE, but may require adjustment to the following parameters to optimize performance: Edit Mode (butt-splice only), Crossfade (Off or 0 ms), and Error Correct (Correct, not Conceal).
Note: If this tape was played back through a plant capable of passing only 16-bit audio, the Dolby E track would be truncated and the tape rendered useless.
20-bit:Default value allows Dolby E encoding of up to eight channels into a 1.9 Mbps AES pair.
16-bit:Allows Dolby E encoding of up to six channels into a 1.5 Mbps AES pair.
