Soft Limiter; Optional Analogue To Digital Converter (Adc) - Focusrite ISA 430 MKII User Manual

Soft Limiter

applied to them, signal levels between –4dBFS and 0dBFS
have a ratio of 2:1 applied to them, and signal levels
between 0dBFS and +6dBFS have a ratio of infinite:1 applied
to them.
The attack and release times for the limiter are
instantaneous. This means that the audio is "clamped down"
so that the signal can never go above the maximum level
that the ADC can accurately convert (0dBFS).
Consequently, it is impossible to overload the connected
optional ADC card when the soft limiter is active.
Optional Analogue to Digital
Converter (ADC)
The ISA 430 MKII can be used as a high quality two-channel
ADC to convert analogue signals to the digital domain, by
adding the optional ISA 430 MKII digital output board. The
two external ADC inputs and the main channel inputs can
all be fed to the ADC, via the soft limiter, ensuring super-
clean, protected, high-quality digital conversion.
Alternatively, two ISA 430 MKII units with a single A/D
option can be used to create a stereo tracking/mixdown to
digital system (see 'Stereo ISA 430 MKII Units' on page 20).
Digital formats available on the ADC are AES, SPDIF
(optical and coaxial RCA phono) and ADAT™ optical
format. (The ADAT™ outputs can also operate in high
speed SMUX mode for 96kHz transfer speeds, but are
muted during 192kHz operation.) N.B. If RCA phono
(SPDIF) or XLR (AES) connections are required, the
relevant 9-pin D-type to RCA phono or XLR breakout
cable is required. For installation details, see separate A/D
option user guide.
ADC Input 1 and 2
With the ADC Input 1 and 2 switches both unlit,
whatever is connected to the mic, line or instrument input
feeds the main analogue output, and also feeds the left side
of the A/D converter. Both signals are post-processing. A
pre-processed signal is fed to the post-mic output, and this
pre-processed signal is also fed to the right side of the A/D
converter.
With the ADC Input 1 switch lit and ADC Input 2
switch unlit, whatever is connected to ADC input 1 cuts
Press to activate the soft limiter.
The soft limiter circuit acts by
gradually increasing the ratio of
the limiter as the signal exceeds
the threshold. The threshold is
set at –6dBFS (+16dBu). Signal
levels between –6dBFS and
–4dBFS have a ratio of 1.5:1
whatever is connected to the mic, line or instrument input,
and feeds the left side of the A/D converter in its place. The
pre-processed signal is still fed to the post-mic output, and
this is still also fed to the right side of the A/D converter.
With the ADC Input 1 switch unlit and ADC Input
2 switch lit, whatever is connected to the mic, line or
instrument input feeds the main analogue output, and feeds
the left side of the A/D converter. Both signals are post-
processing. Whatever is connected to ADC input 2 cuts the
unprocessed signal fed from the mic, line or instrument
input, and feeds the right side of the A/D converter in its
place.
With ADC Input 1 and 2 switches both lit,
whatever is connected to ADC input 1 cuts whatever is
connected to the mic, line or instrument input, and feeds
the left side of the A/D converter in its place. Whatever is
connected to ADC input 2 cuts the unprocessed signal fed
from the mic, line or instrument input, and feeds the right
side of the A/D converter in its place. See ADC
Configurations diagrams on page 15.
24-bit/96kHz ADAT™ (optical/
lightpipe) interface operation
The card provides digital outputs for both ISA 430 MKII
ADC input channels, which operate over the sample
frequency ranges 44.1, 48, 88.2 and 96kHz, and can be
dithered to 16-, 20-, or 24-bit depths depending upon the
destination. The card features an ADAT™-type 'lightpipe'
output and SPDIF Toslink output connectors. ADAT™
lightpipe cables are available from your local dealer, or in
the UK from Studiospares (tel +44 (0)20 7482 1692): stock
number 585-510.
24-bit/192kHz AES/SPDIF operation
The card also provides AES and SPDIF format outputs via a
9-pin D-type connector on the rear panel. The full range of
sample rates (up to 192kHz) and bit depths are available. To
access the digital signals from the 9-pin D-type output
connector, the A/D card must be purchased with either an
AES or SPDIF D-type conversion cable as follows:
AES cable: 9-pin D-type to 4 male XLR
SPDIF cable: 9-pin D-type to 4 male RCA phono
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