Focusrite ISA430 MkII Recording Channel Focusrite update their

Focusrite ISA430 MkII Recording Channel Focusrite update their
on te st
processor
Focusrite
ISA430 MkII
Recording Channel
Focusrite update their
successful high-end
Producer Pack to keep it
ahead of the game.
Hugh Robjohns
he Focusrite ISA430 has been one of the
most popular of all the recording
channels since its launch nearly five
years ago. Based on designs by Rupert Neve,
it combined a remarkably flexible signal path
with the superb sonics we have come to
associate with the Focusrite marque.
Like many companies at the forefront of
analogue design, Focusrite continue to
develop and refine their circuits, and have
come up with several significant
improvements in the intervening years since
the ISA430 was first introduced. The company
have now decided to add many of these
enhancements and features to an updated
ISA430 MkII, further improving its sound
quality and facilities. The new model also
benefits from enhanced internal signal routing
options, to increase flexibility even more, and
it is also claimed to be easier and more
intuitive to operate.
The ISA430 MkII, like the original, is a 2U
rackmount processor designed to process a
single audio channel. The control layout is
much the same as the original and the unit is
instantly recognisable. Like its predecessor,
the ISA430 MkII features mic, line and
instrument inputs (the last doubled to the
front panel as well as the rear), plus
a comprehensive EQ stage, a compressor, an
expander/gate section, a de-esser, and a soft
peak limiter. The original design was based on
the classic ISA110 mic preamp and EQ
circuits, and the ISA130 dynamics (with
T
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SOUND ON SOUND • january 2004
Focusrite ISA430 MkII £1874
pros
• Switchable input impedances.
• Mic Air inductor.
• More usable EQ and additional insert options.
• Vintage optical compressor mode and Blend
feature.
• Upgraded A-D card and I/O options.
• Even more flexible and even better sounding!
cons
• A-D card breakout cable at extra cost.
• More complicated to understand, if not to
operate.
summary
This unit is the British standard bearer when it
comes to high-end analogue channel units for the
committed recording engineer. The MkII enhances
the original model in many ways, improving its
sonic quality and flexibility with switchable input
impedances, a Mic Air mode, and an alternative
optical compressor topology.
a solid-state Class-A VCA), plus a bespoke
de-esser and limiter using high-speed
opto-resistors. However, the input stage,
equaliser and compressor in the MkII version
have all enjoyed major overhauls, borrowing
features and circuit improvements from more
recent Focusrite designs.
Although the ISA430 is intended to serve
as a complete channel strip in a box, it can
also be used as separate processors, and to
this end an additional insert point has been
added to enhance accessibility. Used in
combination, the main I/Os and two insert
points now provide discrete access to the mic
preamp, EQ module, and dynamics section
(the compressor, expander/gate, and
de-esser en bloc) — and if the optional stereo
A-D board is installed, that can be accessed
independently too!
Round The Back
Whenever I come across a new piece of
equipment, the first thing I do is take a look at
the rear panel, and the ISA430 MkII boasts
impressive connectivity for a single-channel
preamp. Starting at the right-hand side, the
mic and line inputs are catered for with XLRs,
and an unbalanced quarter-inch socket
provides a high-impedance instrument input.
A TRS socket below the mic input can be used
to independently link the compressor and
gate side-chains with those of a second unit,
for stereo working. Two more TRS sockets
provide balanced line-level key inputs to the
80 Front-panel Controls!
mic, line and instrument sources and the
input impedance options, which are identical
to the ISA428: Low presents 600Ω, ISA is
1400Ω, Medium is a more usual 2400Ω, and
High presents 6800Ω. The Mic Air feature has
been borrowed from the Platinum Twin Trak
Pro, but whereas that design used an
electronically balanced input stage with an
inductor circuit to emulate the ‘air’ of a
transformer input, the ISA430 MkII uses the
parallel inductor circuit coupled into the
secondary of the input transformer. The idea
is to accentuate the inherent HF resonance of
the transformer, creating a brighter and more
‘spacious’ sound — hence the name.
Another change from the original ISA430
design is that the line input now passes
through the transformer as well, but should
a transformerless sound be required, the
entire input stage can be bypassed by using
instead the first insert point, which has an
electronically balanced input buffer. The only
drawback is that this route does not have a
gain control, but that may not be a problem in
practice.
Comprehensive Equalisation
±18dB boost or cut ranges, fully variable
Q (bandwidth), and usefully wide and
overlapping frequency ranges. The lower
band can be adjusted from 40Hz to 400Hz, or
120Hz to 1200Hz if the x3 option is switched
on. The upper band spans 600Hz-6kHz, or
1.8-18kHz with the x3 mode.
The shelving section boasts two new
frequency positions to make the ISA430 MkII a
little more flexible, but without compromising
the fundamental ISA110 circuit design. The
low shelf turns over at 20, 56, 160 and 460Hz
in standard mode, and 33, 95, 270 and 655Hz
in high range. The high shelf is provided with
frequencies of 1.5, 3.3, 6.8 and 15kHz in
standard mode and 2.2, 4.7, 10 and 18kHz in
the high range. Again, these are well-chosen
and flexible options.
Dynamics Controls
The dynamics facilities are all arranged along
the bottom half of the control panel, starting
off with three illuminated buttons to configure
the second insert point. Next along is another
button to determine the position of the
dynamics processing within the machine’s
signal path. The default is post-EQ, with
options of pre-EQ and post-sum. The former
should be self-explanatory, while the latter
means that the dynamics section is moved
right up to the output of the unit, immediately
prior to the soft limiter, but after the output
level control and, more importantly, after the
external ADC input, which can be summed to
the final output. This mode enables the
dynamics section to control the mix of
internal and external signals, if required.
Moving on across the front panel, another pair
of illuminated buttons configures the first
insert point, and this is followed by the
equaliser section, which is divided into three
separate elements. The first provides
high-pass and low-pass filters; the second a
pair of parametric mid-sections; and the third
high and low shelf sections. All three elements
can be independently bypassed or switched
into either the compressor or gate side-chains
for frequency-selective dynamics
processing — such as reducing
mic pops from wind blasts, or
implementing creative dynamic
EQ. The entire equaliser section
can also be bypassed with
another illuminated button.
The two filters span
20Hz-1.6kHz and 400Hz-20kHz,
respectively, with 18dB/octave
slopes, and allow excellent
control of out-of-band signals, as
well as providing useful
band-pass filtering for dynamic
The preamp section now includes a new Mic Air function, developed
side-chain applications. The
from a similar feature on the Platinum Twin Trak Pro, as well as the
mid-band parametrics are as
facility to select different mic input impedances, previously only
available on the company’s ISA428 four-channel preamp.
comprehensive as ever, with
january 2004 • SOUND ON SOUND
63
▲
The ISA430 MkII front panel is even more
complicated than the original design, thanks
to the additional features and facilities which
Focusrite have managed to cram on! I counted
80 separate knobs and buttons — so be
prepared to spend more time than usual
familiarising yourself with the operation of
this product. Fortunately, things are mostly
logical and intuitive, and the panel is clearly
marked and well laid out. The
signal-processing sections kick off with the
input stage in the top left-hand corner. The
transformer-balanced input circuitry features
additional switched impedance facilities from
the ISA428, and the Air feature from the
Platinum-series Twin Trak Pro.
The panel controls include two rotary
knobs for coarse and fine gain, plus four
illuminated buttons which select high-gain
mode, phantom power, the Mic Air function,
and phase reverse. For the mic input, the
switched gain control operates in 10dB steps
between zero and 30dB, or 30dB and 60dB in
high-gain mode — there is no pad switch. The
line input gain can be varied from +10dB to
-20dB, and both can be adjusted further, with
the continuous fine gain control, from zero to
+20dB. If the instrument input is selected,
then this is controlled with the fine gain knob,
its range spanning +10dB to +40dB.
Two more black buttons cycle through the
Photos: Mark Ewing
compressor and gate — a useful facility.
Next along the top row is a male XLR
providing a direct output from the preamp
section of the unit, and this is followed by two
pairs of XLRs forming the two balanced insert
sends and returns. This is probably the most
complicated aspect of the entire unit — have
a look at the ‘Insert Possibilities’ box to see
how much flexibility is on offer.
The last connector on the top row is
another male XLR, providing the main
balanced output after all the signal
processing. Below this are two more female
XLRs which access the optional A-D card
inputs, via the soft limiter. A pair of
front-panel buttons independently select these
rear-panel inputs in place of the normalled
internal signals (processed output to channel
one and preamp direct out to channel two). In
this way, both clean and processed versions
of the input signal can be recorded easily to
a DAW, if required, and I think this is an
excellent facility. However, a signal connected
to the first ADC input can also be mixed
internally with the processed signal, and the
combined sum passed on to the main
analogue balanced output and A-D converter.
To the right-hand side of the unit is a slot for
the optional A-D card, as well as the IEC mains
inlet with its integral fuse holder and mains
voltage selector.
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FOCUSRITE ISA430 MKII
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The compressor section has been updated
with two alternative gain-control elements.
The default mode uses the familiar Focusrite
VCA design, employing discrete Class-A
circuitry, but the alternative provides a
high-speed optical element for gain reduction
which brings a distinctive vintage sound
quality to the dynamic control. Furthermore,
the circuit topography of these two modes is
entirely different. The VCA circuit uses a feedforward side-chain which controls the VCA
from the input signal, whereas the optical
circuit uses a feed-back side-chain, controlling
the light-dependent resistors from the output
signal. These provide very different sonic
characteristics, adding to the colour and
character of this unit.
The compressor controls comprise the
usual set, but the control ranges change
between VCA and optical mode. For the VCA
configuration, the threshold spans -28 to
+12dBu; the ratio ranges from 1.5:1 to 10:1
with a soft knee; the attack is variable
between 100µs and 100ms; and release varies
from 100ms to 7s, with an optional automatic
programme-dependent mode. Up to 20dB of
make-up gain can also be added. In the
Vintage optical mode the threshold range is
the same, but the attack and release times are
fixed. The ratio is controlled in two stages:
1.5:1 to 5:1 in compressor mode with a soft
knee, or 5:1 to 20:1 in limiter mode with
a hard knee.
Two illuminated buttons bypass the
compressor and allow the side-chain to be
auditioned (useful when trying to fine-tune an
equaliser in the chain), and a third activates
the external key input for voice-over or
auto-ducking applications, or
frequency-conscious dynamic control using an
external equaliser or some other control
signal. However, the external key cannot be
used with the vintage optical compressor
mode.
Other new features added to the ISA430
MkII are Blend and Mix controls — borrowed
from the ISA220. Pressing the illuminated
Blend button causes the Mix control to mix the
compressed signal with the original input
signal, in any proportion. The idea is to make
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SOUND ON SOUND • january 2004
An optional A-D converter, with essentially the
same design as that employed in the ISA428, can
be installed to provide a two-channel digital
output at up to 192kHz sample rates and with
24-bit word lengths. ADAT lightpipe, S/PDIF
optical and AES-EBU outputs are provided, and
the AES-EBU output can be switched to give
a coaxial S/PDIF-formatted signal if required.
However, to access the
AES-EBU or S/PDIF
coaxial outputs, a
special breakout cable
is required to interface
with the nine-pin D-Sub
socket. This cable is
not supplied with the
A-D card, and has to be purchased separately.
Sadly, the pin configuration is not given in the
handbook, making it difficult to construct your
own breakout cable.
The ADAT port supports the SMux mode to
transfer 96kHz audio if required, and the AES-EBU
output can be configured to operate in either
it easy to implement ‘parallel compression’ — a
particularly subtle form of gentle ‘bottom-up’
compression widely used in classical music
recording circles. However, because the
expander/gate section shares the same
gain-control element, using the Blend control
will inherently reduce the effectiveness of the
gate process, since a proportion of the original
signal is being mixed back into the output
signal. In general, though, I think it unlikely
that anyone will want to use the gate at the
same time as applying subtle parallel
compression, so this conflict of interests is
unlikely to be a problem.
The expander/gate is equipped with
controls for Range (0-80dB); Threshold
(+10dBu to -40dBu); Hold (20ms-4s); and
Release (0.1-5s). In addition, illuminated
buttons select Bypass, Expander mode (the
default is to operate as a gate), side-chain
Listen, External Key, Fast Attack, and
Hysteresis. The last increases the level
difference between the gate opening and
closing, which helps prevent the gate from
‘chattering’ on slowly changing signals. A row
of five green LEDs shows the amount of gain
reduction being applied.
The de-esser section is next in line, and
this features just Frequency (2.2-9.2kHz) and
Threshold controls (+10dbu to -20dBu). As
single- or dual-wire (double-wide) modes for all
sample rates up to 192kHz. Word-clock I/O is
catered for with the usual BNC sockets for
external clock-synchronisation duties.
The AES-EBU to S/PDIF format conversion and
single-/dual-wire modes are selected via buttons
on the card’s rear panel, but all the other
functions are controlled from a section of the
ISA430 MkII front panel. Three buttons toggle
through the various options: the first cycling
around the six sample rates (44.1, 48, 88.2, 96,
176.4, 192kHz); and the second selecting the
word length (16, 20 or 24 bits). Another button
determines the clock reference (internal, external
or external x256 Super Clock).
always, illuminated buttons bypass the
de-esser and enable the side-chain to be
auditioned to make tuning easier. A red LED
illuminates when gain reduction is applied,
the intensity increasing with the amount of
level reduction. The Focusrite de-esser is
unusual in that it works as a subtractive
process — the sibilant signal is detected in
a side-chain and the unwanted element is then
subtracted from the main signal so that the
latter is affected only at the moment of
sibilant reduction, resulting in a more
transparent process.
The output section boasts a large output
level control spanning +6dB to -60dB, with
a calibrated unity gain mark (but no detent to
hold the control in position). An illuminated
button activates the External Sum mode to
mix a signal connected to the rear-panel ADC
Input 1 with the internal processed signal. The
level of the external signal can be controlled
with a smaller rotary knob, calibrated from
zero to -60dB. A Mute button kills both the
main and post-mic analogue outputs, but not
the insert sends or the digital output.
A Bypass button tucked away in the corner
switches out the entire EQ and dynamics
processing to enable a global
processed/unprocessed comparison, to check
whether quality improvements really have
▲
The flexible EQ section incorporates separate
filtering, parametric EQ, and shelving EQ blocks, each
of which can be switched independently into the
dynamics side-chain if required.
Optional A-D Card
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FOCUSRITE ISA430 MKII
▲
been made or if the source is just louder and
brighter!
The last stage of signal processing is the
soft limiter, activated by a button in the
metering section to the right-hand side. The
limiter circuitry is the same as that used in the
ISA428, and has a preset threshold of -6dBFS
(+16dBu) with a gradually increasing ratio,
which starts at 1.5:1 and rapidly increases to
infinity. This provides very effective overload
protection for the A-D card, as well as
clamping the analogue output to +22dBu.
Metering Facilities
The right-hand side of the unit carries a pair of
vertical bar-graph meters which default to
showing the output and input, respectively, of
the ISA430 MkII signal-processing chain. The
output meter shows the signal level at a point
immediately prior to the A-D converter (if
fitted), while the input meter shows the level
at the output of the preamp (the input to the
EQ and dynamics chain). Alternatively,
pressing a pair of buttons below the meters,
allows the A-D card inputs to be monitored
instead.
Over to the left of the unit is a large VU
meter, the calibration of which can be
configured with a button such that 0VU
equates to either +4dBu or +18dBu — the
latter being more appropriate when
monitoring the hot levels associated with
professional digital recorders. A second
button selects the metered source, with
options of Input (in other words, preamp
output); either insert return; and amount of
compressor gain reduction. A fifth option is
called up automatically when any of the
dynamics-processor Listen buttons are
pressed.
Should the signal level exceed +20dBu (or
6dB below clipping at any point in the
circuitry), then the red overload LED below the
meter illuminates. The signal is monitored at
five key points in the signal path to ensure that
excessive peaks in one part of the unit are not
masked by lower levels in another. Unlike the
ISA220, the status of all of the switches on the
430 MkII is remembered when the unit is
powered up, minimising the frustration caused
by accidental power outages, or when
returning to a session the next day.
On The Session
As with other Focusrite models, the pedigree
of this unit is immediately evident in the clear,
transparent, open and yet full-sounding signal
path — the hallmark of a very high-quality
preamp and processor. The addition of
switchable input impedances will be
appreciated by many, as a useful means to
tailor the sound of a microphone without
resorting to the equaliser. This facility
impressed very much in the ISA428, and its
translation over to the ISA430 is most
welcome. Likewise the Mic Air facility, which
Insert Possibilities
Whereas the original ISA430 had a single,
moveable insert, the MkII benefits from an
additional insert point which has been introduced to
provide more signal routing flexibility and to enable
some extra operational configurations. As a result,
the unit now boasts one fixed and one moveable
insert, making the possible splits and
configurations far more versatile.
When operating in standard mode, insert one
remains before any of the signal processing — the
equaliser and dynamics, regardless of their order
— and after the preamp section. However, the
same insert I/O ports can be linked to the equaliser
section input and output using the EQ Split button
in insert one’s control block on the front panel. In
this mode, the entire equaliser section is separated
from the rest of the signal path (although individual
elements can be switched to the dynamics
side-chains, of course), and the output from the
preamp section is routed directly to the dynamics
processor.
66
SOUND ON SOUND • january 2004
The second insert point can be switched to any
one of four different positions in the signal path. It
can operate as an insert point between the EQ and
dynamics sections, or after the dynamics and
immediately prior to the output control.
Alternatively, it can also be used to provide the I/O
to the separated dynamics section with the
Dynamics Split button.
Further flexibility (or complication, depending on
your point of view) comes from the ability to move
the dynamics section pre-EQ or post-sum. In the
post-compressor insert position, if the dynamics
block is routed post-sum, then the insert falls back
to post-EQ (but still before the output section). On
the other hand, if the dynamics have been switched
pre-EQ, the insert moves to a position between the
dynamics and equaliser sections. It may all sound
very complicated, but the handbook explains the
options well and it results in fantastic flexibility,
allowing virtually any signal path to be constructed
internally or externally.
The dynamics section comprises compressor/limiter
(offering VCA and optical compression flavours),
expander/gate, and de-esser.
I found extremely useful on almost
everything! It is a powerful treatment which
seems to add the illusion of a natural space
around the sound, and I found it particularly
useful when close-miking instruments, to
restore some of the lost brilliance and ‘air’
— I can’t think of a better word! — which is
inherent in such an approach.
The equaliser is essentially unchanged
from previous versions, apart from the
addition of a couple of extra shelf frequencies.
The ISA110 equaliser is rightly acclaimed as
a classic, and the pedigree shows again here.
High-end equalisers like this seem to be able
to make subtle tonal changes without
destroying the homogeneity of the source in
the way that many equalisers do. The
provision of the three separate sections
— filters, parametrics and shelves — and the
ability to split them and allocate them to the
dynamics side-chains, makes this an
immensely flexible unit.
The compressor was always a key element
in the ‘sound’ of the original unit, and
although described as transparent by
Focusrite, I always found the compressor had
a subtle character all of its own. In his review
of the original ISA430, Paul White described
the compressor as sounding ‘effortless and
professional’, and I think that sums it up
admirably — except that it just became
a whole lot better with the addition of the
Vintage mode, providing a rich alternative to
the VCA sound. Optical compressors have
a very recognisable character, especially when
worked hard, often ideally suited to drums
and basses. To have the option of both here is
pure luxury — and this heavenly state of
affairs has been made even better with the
inclusion of the Blend facility. I’ve always been
a big fan of the parallel compression
technique, and the arrangement offered here
is a joy to use. Although I only had the ISA430
MkII for a week or so, I found I used this
facility a great deal.
The gate is one of the nicest available, as
well as being one of the easiest to use — it
really just does the job asked of it without
fuss, and operates in a reliable manner,
especially with the Hysteresis mode engaged
to reduce the possibility of false triggering on
slowly decaying sounds. The ability to quickly
flip the filters or parametric equaliser
provide the most complete and
into the side-chain to tidy up the
superb-sounding channel path
control signal is also very useful. I am
available, and it does that in spades.
always amazed at how hard the
While a large percentage of sales will
de-esser can be made to work with
be to pro freelance producers and
minimal side effects, and the
engineers as well as studios and
provision of the side-chain listen
remix rooms, I should think a similar
facility makes finding the offending
volume will be sold to home and
sibilant frequencies very
project studios that need just one
Next to the output-level controls are buttons allowing you to set the sample
straightforward.
really good front-end unit — and with
rate and bit depth of the optional A-D converter board. You can also activate
the soft limiter from here.
The inclusion of the external input
the optional A-D card, the ISA430 MkII
and summing mode will be useful to
has to be one of the best and most
many, but personally I think the provision of
was going to be something special. Taking the
versatile units on the market today. I can’t
external inputs to the optional A-D card is
features of the original unit and adding all the
think of anything negative to say about the
benefit enough. The soft limiter did the same
new tweaks and technologies that the
ISA430 MkII — it really is that impressive.
sterling job here as it did on the ISA428. I tend
Focusrite back-room boys have developed
Committed recording engineers now have a
to leave a modest headroom when I’m working
subsequently has resulted in just about the
new British standard-bearer when it comes to
with digital gear, but this optical limiter does
best possible recipe for a producer channel.
high-end analogue recording channels.
a fantastic job of neatly controlling transient
This is the kind of device that mere mortals
peaks without sounding heavy-handed about
will gladly die for, but only after they have
information
it. For the red-light junkies out there, this is
enjoyed using it for a few decades, naturally!
your saviour — and best of all, most people
Although we are still talking serious
£ ISA430 MkII, £1874.13; optional A-D card,
£323.13; digital breakout cable, £25. Prices
will never know that the concept of headroom
professional gear prices, this is a very
include VAT.
is completely lost on you!
attractively priced unit in the UK, offering
Focusrite +44 (0)1494 462246.
T
even better value for money than the original,
F +44 (0)1494 459920.
A Channel To Die For
with a stunningly high-quality, comprehensive
E sales@focusrite.com
There was never any doubt in my mind (or
and extraordinarily flexible package.
W www.focusrite.com
I suppose anyone else’s) that the ISA430 MkII
The ISA430 MkII has been designed to
january 2004 • SOUND ON SOUND
67
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