Prism Sound Dre: 'Dynamic Range Enhancement; Using Prism Sound Dre With The Ada-8; Prism Sound Overkiller - Prism Sound ADA-8 Operation Manual

Prism Sound ADA-8 Multi-channel A/D D/A Converter Operation Manual - Revision 1.00
levels in the usual way. However, don't be surprised to see random deflections on the other
channels' meters – these indicate the presence of the secondary tracks and tag.
Obviously for correct reconstruction of the audio data, it is important that the replay or
transmission path includes all eight tracks, otherwise an incorrect Track Mode might be
decoded or low-order bits lost. This makes it inadvisable to record tracks individually or at
different times on a multi-track tape recorder although, with care, it can be done. In the four-
channel mode, record channels 1 and 5 together, channels 2 and 6 together, etc; channels 4
and 8 should be recorded first to lay down a continuous Track Mode tag. In the six-channel
modes channels 1, 3, 5 and 7 should be recorded together, with channels 2, 4, 6 and 8
recorded first to lay down the tag.

7.4.3 Prism Sound DRE: 'Dynamic Range Enhancement'

Prism Sound DRE (Dynamic Range Enhancement) was devised as an encoding scheme for
representing extended wordlengths on a 16-bit recorder or transmission channel, but without
the need to sacrifice channels.
This requirement obviously means that precise data cannot be reconstituted under all
circumstances. DRE works by ensuring that precise data IS reconstituted for small and
moderate signal levels (up to about 20dB below peak) and that loss of data is optimally
concealed above that point. This criterion was in response to existing sub-band ('perceptual')
coding systems which have unsatisfactory small-signal performance. Subjectively, DRE
allows 16-bit media (such as DAT or CD-R) to be used to make recordings indistinguishable
from 20-bit recordings.
The ADA-8 also features an extended version of DRE, optimised for use with 20-bit media. In
view of this extension to the format, the original DRE for 16-bit media is now referred to as
DRE , and the new extension for 20-bit media is known as DRE .
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7.4.4 Using Prism Sound DRE with the ADA-8

DRE encoding is selected within the Dither/Encode box of the Mimic Panel as described in
section 5.1.4. DRE encoding is indicated by the 'DRE' LED being lit; if the '[20b]' LED
beneath is also lit, DRE encoding is indicated, otherwise DRE encoding is indicated.
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When selecting DRE encoding, DRE or DRE mode must be explicitly selected.
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DRE decoding is selected within the Decode box of the Mimic Panel as described in section
5.1.2. DRE decoding is indicated by the 'DRE' LED being lit. Note that the decoding
algorithm is common for DRE and DRE data, so it is not necessary to distinguish which is
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to be decoded.
Note that DRE encoded data cannot be metered accurately at the recorder or transmission
channel. Although the audio envelope is approximately maintained in the encoded data,
levels are not as metered.

7.5 Prism Sound Overkiller

The Prism Sound Overkiller is a progressive analogue peak-limiter which can be applied to
any of the ADA-8's analogue input channels, so long as a suitably-equipped Analogue Input
Module is fitted. The Overkiller allows analogue input signals far above the normal maximum
handling level of the A/D converter to be accommodated without causing the converter to clip.
This is done in a gentle and progressive manner so that distortion is as inaudible as possible.
© Prism Media Products Limited, 2002 Page 1.33