Process Box; Dither/Encode Box - Prism Sound ADA-8 Operation Manual

Prism Sound ADA-8 Multi-channel A/D D/A Converter Operation Manual - Revision 1.00

5.1.3 Process box

The Process box indicates whether any of the Path's channels have any functions of the
Processing Suite activated. The processing Suite is a range of signal processing functions
which are available if the DSP Expansion Module is fitted inside the ADA-8. The Process
box's Access button attracts the attention of the Menu panel immediately to the group of
menus that control the Processing Suite if it is available (otherwise an explanatory message is
displayed). For details of these menus, see the Firmware Reference.
The 'Patch' LED is lit to indicate that some cross-channel patching or mixing is selected. The
'Process' LED shows that signal processing functions are active. Otherwise, the 'Bypass'
LED confirms that no patching or processing is enabled.

5.1.4 Dither/Encode box

The Dither/Encode box indicates the wordlength of the Path's digital outputs (if digital outputs
are assigned), and also any encode algorithms which are in use. The Dither/Encode box's
Access button attracts the attention of the Menu panel immediately to the small group of
menus that control output wordlength and encoding algorithms. For details of these menus,
see the Firmware Reference.
The column of green LEDs in the middle of the box show the wordlength of the digital audio
channels being output. More than one of these LEDs might be illuminated if more than one
wordlength range has been selected for different output channels of the Path. The 'SNS' LED
to the left is illuminated if any of the channels has has wordlength reduction using the Prism
Sound Super Noise Shaping algorithm selected. The 'Flat' LED is lit if any of the Path's
channels have only flat dither selected. The Prism Sound Super Noise Shaping process is
described in detail in section 7.3.
The 'Auto' LED is lit to indicate that 'Auto Dither Defeat' is active. Auto Dither Defeat is an
algorithm which prevents unnecessary or undesirable dithering or noise shaping being
applied to the channels of a digital-to-digital Path. This happens in one of two situations.
Firstly, if the incoming wordlength is less than or equal to the desired output wordlength, it is
unnecessary to add further dither or noise shaping, since no truncation of the wordlength is
implied. To add further dither or noise shaping would merely increase the noise floor of the
signal without benefit. The second situation occurs if the incoming audio data is 'digital black'
i.e. all the audio data bits are zero. In this situation, it is undesirable to add dither to the
outgoing audio since 'black-in-black-out' operation is useful when compiling tracks etc. Some
older editing systems require 'black-in-black-out' behaviour to recognise track boundaries.
Note that digital black input is assumed after 10000 consecutive zero samples have been
received, and is cancelled immediately on receipt of a non-zero sample. Note that, in fact, the
second situation is really a subset of the first since black audio data has essentially zero-bit
wordlength. The Auto LED is lit when ALL active channels in the Path are in Auto Dither
Defeat mode.
The 'MR-X' LED shows that the output port is being encoded using the Prism Sound MR-X
format, which is a word-mapping scheme whereby, for example, a multi-channel digital
recorder can be used to record longer wordlengths and/or higher sample rates than its native
format by sacrificing tracks. 'MR-X ' is the variant of this format for recorders (or data
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channels) with a maximum 16-bit wordlength, whereas 'MR-X ' is used for 20-bit media
20
where less track sacrificing results. The '[20b]' LED shows that 'MR-X ' encoding is taking
20
place, whereas the 'MR-X' LED without the '[20b]' LED shows 'MR-X ' encoding. The Prism
16
Sound MR-X encoding scheme is described in detail in section 7.4.
The 'DRE' LED shows that one or more of the input channels are being encoded using the
Prism Sound DRE (Dynamic Range Enhancement) format, which is a coding scheme to allow
extended wordlengths to be recorded on a medium (or passed down a digital channel)
© Prism Media Products Limited, 2002 Page 1.17