WEISS GAMBIT ADC2, Operating Manual

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OPERATING INSTRUCTIONS FOR GAMBIT ADC2 24Bit / 192kHz A/D CONVERTER OPERATION
Daniel Weiss Engineering Ltd., Florastr. 42, CH-8610 Uster Page 7
+41 1 940 20 06 +41 1 940 22 14 http://www.weiss. ch weiss@weiss.ch
Sync and Dither Control Panel
Fig. 6 ADC2 Sync and Dither Control Panel
Sampling Frequency
If the analogue inputs are selected (“ digital in ” is not
lit), the A/D sampling frequency can be set in the sync
source block:
Sampling Fre-
quency
44.1 / 48 kHz
key
fs x 2 / fs x 4 key
44.1 kHz 44.1 kHz none
48.0 kHz 48 kHz none
88.2 kHz 44.1 kHz sf x 2
96.0 kHz 48 kHz sf x 2
176.4 kHz 44.1 kHz sf x 4
192.0 kHz 48 kHz sf x 4
Table 1 Samplig Frequency Selection
If “ digital in ” is lit, the sampling frequency keys display
the sampling frequency of the AES/EBU input signal in
the same fashion as is shown in Table 1.
Sync Source
As can be seen in Fig. 1, the ADC2 can be synchronized
externally by other digital devices. It has two external
sync inputs. External sync is only available for ana-
logue inputs, ie “
digital in ” key is not lit.
If “ AES ” is lit, the AES/EBU signal at the “DI 1 / SYNC ”
input is used for synchronization. If “ BNC ” is lit, the
wordclock signal connected to “ WORDSYNC in ” is used
for synchronization. Both sync inputs have a loop-
through ouput to syncronize other devices.
If none of these two keys are lit, the ADC2 uses inter-
nal sync.
POW-r Dither
To requantize the input signal from 24bit to 16bit
format, a special technique is used to avoid distortion,
called dithering. Many dithering schemes are available
today, both professional and homebrewed. The ADC2
uses the POW-r scheme, which is widely regarded as
one of the best, if not the best
2
, and is used in a varie-
ty of digital equipment.
The POW-r scheme offers three different presets
which can be selected with the dither keys “
pow-r 1 ”,
“ pow-r 2 ” and “ pow-r 3 ”. The choice should be based
on listening tests and preference of the recording
engineer
.
Dithering is in “auto black”
3
mode: if digital zero is
detected at the ouput, dithering is switched off. This
ensures that programme breaks are not filled with
dither noise.
“Auto black” mode is not available for analogue input
signals.
Also note the effect of the “DITHER MODE” dip switch
setting in Fig. 1 ADC2 Block Diagram Schematic. If the
dip switch is in the down position, requantisation to
16 bit and dithering is only applied to the S/PDIF RCA
output, whereas the AES/EBU XLR output still carries
all 24bits. This mode is useful for live recording to a
24bit device with simultaneous backup to a 16bit
device (like DAT or CD-R). If the dip switch is in the up
position, all digital outputs are dithered to 16bits.
2
For reviews of POW-r visit www.weiss.ch
3
The term “black” comes from digital image formats, where
black is represented by the value zero.