Focusrite ISA430 Producer Pack

Focusrite's latest product is an updated version of one of their '80s classics. Is it even better the second time around?

If the new ISA430 Producer Pack looks in any way familiar, it's because both the circuitry and cosmetics are based on Focusrite's mid‑'80s, Rupert Neve‑designed vertical modular rack Producer Pack system. Essentially, the unit comprises a mic/line/instrument front end teamed with a compressor, an equaliser, an expander/gate, a de‑esser and a limiter. An optional dual‑channel digital output stage will be available imminently, but was not ready at the time of this review.

The mic preamp and parametric EQ sections are lifted directly from Focusrite's old ISA110, and both the compressor and gate are derived from the ISA130. However, vintage is not always best, and in recent years, Focusrite have developed their own Class a VCA which has a significantly better audio performance than its predecessors, so the new VCA has been used instead of the original. Furthermore, the de‑esser and limiter are brand‑new designs based on recently developed high‑speed optical components, and Focusrite claim that they perform significantly better than the original circuits in all respects. Focusrite have worked closely with the manufacturers of their opto components, and I'm told that because the technology is being driven by the fibre‑optics industry, tremendous improvements have been made, especially in speed of operation, where opto devices were traditionally quite slow. The transformers used in the mic and output stage are built to exactly the same design, and manufactured by the same company, as originals.

Housed in a 2U rack case, the ISA430 is a single‑channel analogue signal processor, which has a section of the rear panel reserved for the optional digital output stage. This will support all the popular sample rates and bit depths from 16‑bit, 44.1kHz up to 24‑bit, 96kHz. a matrix of front‑panel LEDs shows the current sample rate and bit depth, while momentary action switches allow the clock rate, bit depth and sync source to be set up. The unit can either sync internally, lock to an incoming digital signal or sync to word clock. Digidesign's proprietary Super Clock is also supported.

Path Of Glory?

The signal chain starts with a mic/line/instrument preamp controlled by switchable mic and line gain pots, augmented by a variable gain trim control. Phantom power and phase reverse are available, though the design precludes the need for pad switches. An unbalanced high‑impedance instrument jack is provided on the front panel for recording instruments such as electric guitar or bass. a large VU meter may be switched to read the input signal level, the insert return level or the compressor gain‑reduction, while dual bar‑graph meters monitor the signal level at the A‑D converter input points, whether a converter is fitted or not. When two units are linked for stereo, the two meters monitor the stereo signal level.

Following the preamp stage is a comprehensive EQ section comprising a pair of variable‑frequency, 18dB/octave high‑pass and low‑pass filters, followed by two fully parametric sections and a pair of high‑pass and low‑pass shelving filters. An All EQ button places the whole EQ section in or out of the audio circuit but doesn't affect any sections that have been switched to operate in the compressor or gate side‑chains. Each individual filter section also has its own bypass button.

The two 18dB/octave filters may be used in the main signal path, the gate side‑chain or the compressor side‑chain and cover the frequency ranges 20Hz to 1.6kHz and 400Hz to 22kHz. The following two‑band parametric section may also be switched into the compressor or gate side‑chain for frequency‑sensitive applications such as de‑essing, de‑popping, dynamic EQ effects or frequency‑conscious gating, though a separate, dedicated de‑esser section is also provided.

A x3 button is included for each of the fully parametric sections to give two possible frequency ranges for each equaliser, in order to avoid the situation where the travel of one control encompasses too wide a frequency range, which obviously makes setting up more fiddly. The first band covers 40Hz to 400Hz (120Hz to 1.2kHz with the x3 switch in) while the second covers 600Hz to 6kHz (1.8kHz to 18kHz).

The final section of the equaliser comprises the two variable‑frequency shelving filters, and it is these that get Neve EQ fans excited. The low filter covers the range 33 to 460Hz and the high filter 3.3 to 18kHz. Rather than use variable controls, the filters are switched over six frequency values, just as in the original Neve design, which means separate filter components can be employed for each frequency. This is rather more costly than using a variable filter, but you don't have to listen for long to know that it's worth the trouble. There are switches to allow the shelving EQs to be placed in the gate or compressor side‑chain, though it would be sacrilege to do so — rather like using a Monet to wrap chips in!

There are switches to allow the shelving EQs to be placed in the gate or compressor side‑chain, though it would be sacrilege to do so — rather like using a Monet to wrap chips in!

Although the compressor has a ratio control, it actually has a soft‑knee characteristic. All the usual Attack, Release, Threshold and Make‑up gain controls are present alongside Ratio and Bypass, but there's no hard/soft‑knee switching. When the Release control is set fully clockwise, an auto release time mode is engaged. This compressor sounds great just as it is, and the Focusrite design team have wisely resisted the temptation to mess with it, other than to upgrade the VCA to one that can do justice to the optional digital output stage.

As well as the capacity to switch any or all of the EQ blocks into the compressor side‑chain, there's also an external key facility and a rear‑panel linking option that allows two ISA430 Producer Packs to run as a stereo pair. The output limiter stage actually has two channels so that when two units are being used as a stereo pair, the limiters within the master unit handle both channels. a listen button allows the compressor side‑chain signal to be monitored, post any EQ that may be inserted.

Next in line is the gate/expander, which again may make use of any or all EQ sections in the side‑chain, and which has the benefit of the Listen button as well as a Bypass button. Most of the facilities are self‑explanatory — Range, Threshold, Hold and Release. a Fast switch takes the place of a variable attack control and there's a switch for external keying, but what may not be so obvious is the Hysteresis button. If a gate is designed to have a single threshold that determines when the gate opens and closes, signals with level modulation can cause the gate to open and close rapidly several times as the signal undulates around the threshold point. This is known as chattering and is especially noticeable at fast release settings. Most modern gates are designed so that a higher signal level is needed to open the gate than to close it — effectively, there are two threshold levels, the higher one being used to open the gate and the lower one to close it. Usually, there is a 5 or 6dB difference between these thresholds, which is enough to stop chattering in most situations. On the ISA430 Producer Pack, the amount of hysteresis (the difference between the open/close thresholds) may be further increased by several dBs via the Hyst button, the idea being that this setting may be more suitable for difficult sounds that have a strong percussive attack.

It may come as a surprise that after all this vintage circuitry comes a de‑esser that owes more than a little to the design used in the Focusrite Platinum range. Older de‑essers often cause lisping effects, as they tended to affect the level of the whole signal rather than just the sibilance, but the new opto‑based design is much better. Instead of placing a VCA in the signal path, the de‑essing is done in a side‑chain that detects high levels at sibilant frequencies, then subtracts them from the main signal using a phase‑cancellation system. The result is that only the sibilant frequency range is attenuated, and any artifacts introduced by the processing electronics only affect the signal during the time de‑essing is taking place. The only controls are Frequency (2.2kHz to 9.2kHz) and Threshold; a Listen button allows the side‑chain signal to be monitored so the user can really home in on the sibilance with the frequency control. As with all the other blocks, there's a bypass button.

The limiter section (which, as mentioned earlier, actually comprises two channels) looks extremely simple, but behind the panel is a sophisticated three‑band system, again based on fast opto‑electronic devices. The time constants for each band are optimised internally so all the user needs to do is set the (pre‑limiter) signal output level. An upper limit threshold of +20dB prevents the optional digital converters from being overloaded. Limit Bypass and output Mute buttons are fitted. Finally comes a control to set the external analogue input level. There are several routing options associated with the external input — see the 'Routing & I/O' box, right.

Using The ISA 430

I was fortunate enough to be able to use the ISA430 in my studio for a couple of days to record vocals, miked acoustic guitar and DI'd electric guitar. As you'd expect from a unit with this kind of pedigree, the signal path is exceptionally clean and transparent with a very low noise level, due in part to the use of carefully specified transformers and wide‑bandwidth circuitry. When trying out the equaliser, the first thing you notice is that it seems very gentle. You can heap on lots of cut or boost and bring about quite radical tonal changes, but the integrity of the original signal always stays intact. With lesser equalisers, you only have to apply a little EQ and the sound starts to get harsh, boomy, smeary or phasey, but here the result is just what you want it to be.

I was also impressed with the compressor. It's definitely designed to be heard rather than sit in the background looking after routine gain‑levelling, and when you work it hard, the side effects are both obvious and very musical. You can add sustain and attack to guitars and basses without losing any life from the sound, while vocals come over as mellifluous and confident. Everything about the sound is effortless and professional. Best of all, it's very easy to find the right controls and arrive at a good sound — you don't need to be an experienced engineer to get good results from this box.

There are switches to allow the shelving EQs to be placed in the gate or compressor side‑chain, though it would be sacrilege to do so — rather like using a Monet to wrap chips in!

Similarly, the gate section behaves smoothly and predictably, and because you can switch chunks of EQ into the side‑chain, frequency‑conscious gating is easy to set up. My personal preference is to use the sharp 18dB/octave shelving filters for this. The switchable additional hysteresis can help when you're trying to separate awkward sounds or percussive sounds with an undulating decay, but most of the time the regular mode works fine.

I had no problems with the de‑esser either: even quite heavy de‑essing has little effect on the subjective vocal sound, which doesn't lisp or go dull as only a relatively narrow band of frequencies are attenuated. Having a listen mode makes it easy to home in on the offending frequency, so setting up is straightforward. All you really need to do is decide how much de‑essing you can get away with before you think the original sound starts to show signs of being processed.

In normal use, I didn't find the limiter had much to do, but when you do push up the signal level so that the peaks are brushing the limiter threshold, it deals with them pretty kindly. It's possible to limit the top few dBs of most material that contains dynamic peaks without the sound appearing to have been processed, the result being that the average loudness can be increased significantly before the limiting starts to show. Having a three‑band system helps, as you don't find the high end suffering whenever a loud kick drum comes along.

Conclusion

I had no doubt when I opened the box that this would be a very nice unit indeed, and I wasn't disappointed. Even without accounting for inflation, it is significantly less expensive than the original Producer Pack equivalent. However, it'll still cost you around as much as a complete desktop studio system based on a nice new G3 or G4 Mac. And if you want stereo, you're into serious used‑car territory! Still, the whole point of this unit is to give discerning professionals the best possible tools to do what is often a very difficult job, and as esoteric analogue gear goes, the price isn't unduly high. In fact a surprising amount of high‑end Focusrite gear appears in privately owned studios.

There are those who would prefer vintage designs to be left exactly as they were, but I feel the new VCAs and improved de‑esser/limiter sections are well justified, as they improve the overall performance without actually changing the characteristic sound. The panel layout makes it easy to locate the different sections very quickly, and though the various routing options can be confusing at first, a quick glance at the block diagram in the manual makes things a lot clearer. This is a first‑rate piece of studio gear and is a perfect illustration of why high‑end analogue is still the preferred choice for serious audio processing.