Prism Sound Mr-X And Dre Encoding Processes; Prism Sound Mr-X - Prism Sound ADA-8 Operation Manual

Prism Sound ADA-8 Multi-channel A/D D/A Converter

7.4 Prism Sound MR-X and DRE encoding processes

Section 7.3 was concerned with limitations in signal quality imposed by restricted audio
wordlengths, and described the dithering and noise-shaping processes which are used at
points of wordlength reduction in order to make the best use of the available wordlength.
Clearly dither and noise-shaping are irreversible processes: the added noise cannot be
removed, the lost bits cannot be recovered. For this reason it makes sense to maintain the
longest possible wordlength throughout the production chain, and to use dithering or noise
shaping as the final step in reducing the wordlength to that of the chosen delivery medium.
This is particularly true of noise shaping, which can be detrimental to subsequent signal
processing.
The problem in maintaining wordlength in the earlier parts of the production chain has often
been the lack of availability of long-wordlength recorders or transmission paths. The ADA-8
incorporates two alternative methods of 'extending' the wordlength of a digital recorder or
transmission channel, each of which can be used with either a 16-bit or a 20-bit medium. The
first, Prism Sound MR-X, is a 'word-mapping' or 'bit splitting' system which allows tracks on a
multi-track medium to be sacrificed in order to make up the extra wordlength. The second,
Prism Sound DRE, requires no track sacrifice and so can be used on stereo media; however,
unlike MR-X, DRE does not guarantee to preserve the precise input data. Both encoding
schemes must be decoded in order to reconstitute the audio signal. The necessary decoders
are also included in the ADA-8.

7.4.1 Prism Sound MR-X

© Prism Media Products Limited, 2002
Originally featured on the Prism Sound MR-2024T Interface
Adapter for Tascam DA-88, the MR-X encoding system
became a de-facto standard for storing 20-bit and 24-bit audio
on MDMs. When the need to pass CD-targetted material with
extended wordlength to mastering studios was recognised, the
MR-X format provided at that time the only cost-effective
medium which was accepted by the world's top mastering
facilities. MR-X is also licensed to other manufacturers of
compatible products.
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