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

Prism Sound ADA-8XR Multi-channel A/D D/A Converter
Note that no wordlength reduction is supported by the ADA-8XR at the '4x' sample-rates
(176.4kHz and 192kHz). The wordlength is fixed at 24-bits at these rates. It is uncommon to
find '4x' recorders or channels which do not support full 24-bit operation.

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 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-8XR 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-8XR.

7.4.1 Prism Sound MR-X

© Prism Media Products Limited, 2001-2004
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
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