ENGLISH
5
Phase
Pressing PHASE inverts the phase of the selected input, to
correct phase problems when using multiple microphones,
or when incorrect wiring polarity has occurred.
Insert In
Pressing the INSERT switch (illuminated) breaks the signal
path of the channel, so that the channel input signal is sent
out of the unit from the rear panel Insert Send connector
and returned to the same point in the signal chain via the
rear panel Insert Return connector.
Filter In
Pressing the FILTER IN switch makes the Hi Pass Filters
active in the audio path. The filter provides 18dB/octave
roll-off. A variable control allows the roll-off frequency to
be set within the range of 16Hz to 420Hz.
Impedance
Pressing IMPEDANCE steps through each of the four
transformer pre-amp input impedance values, as indicated
by the corresponding LEDs. By selecting different values for
the impedance of the ISA 428 transformer input, the
performance of both the ISA 428 pre-amp and the
microphone connected can be tailored to set the desired
level and frequency response.
Analogue to Digital converter (ADC)
Soft Limiter
Pressing ADC SOFT LIMITER activates the ADC Soft
Limiter - giving total protection of all 8 channels on the
ADC.
ADC Soft Limiter Operation
The Soft Limiter circuit acts instantaneously, clamping down
the audio 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. This function is a part of the
ADC signal path, and so only operates when an ADC card
is fitted. If no card is fitted then the switch is inactive.
8 Channel Digital Output Option
The ISA 428 can be used as a high quality 8 channel ADC
for analogue transfer to digital with the addition of the
optional ISA 428 digital output board. The 4 external ADC
inputs and the main channel inputs can all be fed to the
ADC, via the Soft Limiter, ensuring eight super-clean,
protected, high-quality paths to digital. A single ISA 428 unit
can act as an 8-channel digital input expansion unit to any
DAW. Channels 1-4 always route respectively to ADC
output channels 1-4.
Alternatively, two ISA 428 units with a single A/D option
can be used to create an 8-channel mic pre to A/D system
(see ‘Signal Connections’ on page 8). Digital formats
available on the ADC are AES/EBU, SPDIF 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).
24-bit/96kHz ADAT™ interface operation
The card provides digital outputs for all eight ISA 428
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 two ADAT™-type ‘lightpipe’ output
connectors. For speeds up to 48kHz both connectors
transmit all 8 channels simultaneously. However, ADAT™-
type connectors are bandwidth-limited at sample rates
above 48kHz - each audio channel uses two ADAT™ digital
channels to accommodate the increased quantity of data,
hence the need for two ADAT™ connectors to allow 8
channels of conversion at high speed.
The ADAT™ output connectors operate as follows:
44.1/48Khz sample rates:
Connector 1 = channels 1 to 8 in parallel.
Connector 2 = channels 1 to 8 in parallel (identical to
connector 1)
88.2/96Khz sample rates:
Connector 1 = channels 1 to 4.
Connector 2 = channels 5 to 8.
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
two 9-pin D-type connector on the rear panel. The full
range of sample rates (up to 192kHz) and bit depths are
available.
