Dolby Laboratories DP570 Specifications download pdf (Page 7)

Standards and Practices for Authoring Dolby

Digital and Dolby E Bitstreams

3 Perceptual Coding vs. Metadata

It is generally not necessary to monitor the Dolby Digital coding process from encode

to decode simply to preview the effects of the coding algorithm. However, it is very

important to monitor the effects of metadata on the source audio either through the

encode/decode process or through the use of a DP570 Multichannel Audio Tool. The

simple reason is that the Dolby Digital encoding process is specifically designed to be

transparent, while metadata is intended to optimize the program audio for playback in

a variety of home listening environments.

3.1 The Sound of Perceptual Coding as Implemented in

Dolby Digital

Dolby Digital is a data reduction technology that achieves data compression through

the removal of redundant audio information. The audio reproduced through a Dolby

Digital decoder is not identical to the original source audio. During encoding, the

Dolby Digital algorithm selects the portions of the audio that would not normally be

heard by the human ear and removes them through a process known as Perceptual

Coding. Perceptual coding uses the natural properties of the human ear to ignore

signals masked by adjacent frequencies and the differences in level found within full

bandwidth program audio. More information of the specifics of perceptual coding can

be found in several publications on the Dolby website, www.dolby.com.

The Dolby Digital encoded/decoded signal sounds perceptually the same as the original

audio signals. The masking properties of the human ear allow Dolby Digital to achieve a

better than 15:1 compression ratio from original source digital audio with little or no

perceived difference.

The ratio varies based on applicable sampling rates, Dolby Digital data rates, and bit

resolution. Dolby Digital preserves the resolution of the source digital audio.

Note: Sample rate conversion in the DP569 Dolby Digital Multichannel Encoder,

when enabled, limits the encoded signal to a maximum 20-bit resolution.

However, the DP569 is capable of 24-bit resolution when the sample rate

converter is disabled.

The Dolby Digital coding system is designed to preserve the fidelity of the original

source audio, and nearly ten years of critical use by audio professionals in DVD, film,

multimedia, and broadcast has proven it to be a reliable, accurate, and transparent

coding system.

3.2 The Sound of Metadata

Unlike the nuts and bolts of the perceptual coding process, which is designed to be

audibly identical to the source master, metadata is specifically intended to optimize

1 2 3 4 5 6 7 8 ... 26

No comments

Dolby Laboratories DP570 Specifications Page 7