Lake People ADC F29 Bedienungsanleitung Seite 10

HOW IT ALL WORKS....
PREFACE
The ADDAC F29 in both available versions of-
fers high-end technology. By choosing the sui-
table version to meet his specific requirements,
the customer will take advantage of an excel-
lent price/performance ratio. Even the basic
model ADDAC F29-3 is measurably and audibly
better than the middle-of-the-road 16-bit con-
verters usually found in DAT machines, hard-
disk recorders or digital multitrack systems.
Much more important than stating the conver-
ters' available bit width is the maximum achie-
vable dynamic range. We at LAKE PEOPLE
consider this parameter as much more signifi-
cant and honest than the - barely theoretic -
available output bit width.
For those who want to know in detail:
Bitresolution = (dyn. range - 1.76 dB) / 6.02.
This formula leads to an in-fact resolution of
about 16.8 bit for the ADDAC F29-3 and 17.5
bit for the F29-7.
The D-to-A section with its 20-bit converters
measures only 16.6 bit (related to its dynamic
range) or 18 bit (related to the less significant
S/N figure).
There is still to be mentioned, that all our mea-
surements are taken from 20 Hz to 20 kHz. As-
suming an IHF-A weighted measurement, per-
formance would still improve by several dB !
The output word lenght generated is 18 bit for
the F29-3 and 20 bit for F29-7.
A-TO-D CONVERTER FUNCTION
The analog input signals are first buffered, then
their level can be adjusted to the converter's in-
put sensitivity by two pots.
The switchable limiter consists of two symmetri-
cally biased diodes. Factory preset for the li-
miter threshold is 0.3 dB below the converter's
digital full scale.
The unit's core is, of course, the A-to-D conver-
ter chip. It is designed for 1-bit delta/sigma con-
version at 64-times oversampling. Left and right
channel are processed by one and the same
chip.
The incorporated digital filter provides high atte-
nuation of undesirable alias frequencies. The
conversion process is not influenced by the in-
put signal's level or frequency.
The digital output word is available as a serial
signal in two's complement.
For its task, the A-to-D converter requires a
number of clock signals. These are derived ei-
ther from an internal crystal oscillator or from an
external WCLK signal, pre-processed by the in-
ternal PLL circuitry.
Coming from the converter chip, the digital sig-
nal is translated into a form corresponding to
AES/EBU resp. S/P-DIF standard by a further
integrated circuit. After this, it is available at the
corresponding digital outputs on the rear panel.
Different from F29-3, the F29-7 version is
equipped with a pin-compatible improved con-
verter chip. It offers increased dynamic range,
improved stopband rejection and delivers a 20-
bit output word instead of 18-bit. The basic fea-
tures like controls, input circuitry as well as in-
and outputs are identical on both units.
D-TO-A CONVERTER FUNCTION
From the two inputs, the digital input signals are
passed to the ADDAC F29 D-to-A section's re-
ceiver circuit, specially designed for this kind of
signals.
The receiver circuit prepares the signals for
being processed by the following stages. It
scans the incoming data at 64-times oversam-
pling and evaluates the status bits within the
data words (pro/con, emphasis and error). Fur-
thermore, it extracts the sampling rate informati-
on, which is relevant for internal digital proces-
sing speed.
The receiver is followed by the D-to-A conver-
ter. In the F29, it combines a digital filter, the
two-channel converter circuitry and the analog
output filters on one single chip.
The converter operates in delta/sigma mode at
128-times oversampling. Thus, the internal fre-
quencies are extremely high, compared to the
resulting audio signal. Therefore, there is no
need for sophisticated high-attenuation analog
low-pass filters. The F29 employs two-pole fil-
ters in conventional design.
After the filter section and the output level trim-
mers, the analog signals are fed to the balan-
ced and unbalanced output terminals.
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