Hands-On Review:The channel strip done right!

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By Michael O'Brien


Aimed squarely at the project studio market, the ISA220 inherits most of the key features of its big brother, the ISA430 - minus some of the tweakier bits. That's not to say the ISA220 is a lightweight. The mic pre, EQ, and compressor are all of Rupert Neve design and it features multiple inputs with ample gain to cover virtually all your pre-amp needs. A large, illuminated VU meter and a 16-stage LED ladder provide excellent monitoring of levels and compression. The EQ module provides enough control to give you everything from subtle enhancement to radical tone shaping, and a dedicated de-essing circuit makes the task of taming sibilance painless. The compressor not only gives you all the control you would expect from a channel strip of this caliber, it also adds a blend function that truly puts it in a league of its own. And finally, a switchable, multi-band limiter gives you transparent control of the final output.


Click Here.Fit and feel
The familiar rows of yellow knobs on a field of blue and gray let me know I was in Focusrite territory from the moment I removed the ISA220 from its box. It features solid construction, and the controls have a firm, precise feel. The main Gain control is stepped to deliver precise, repeatable amounts of gain, and the EQ boost-cut knobs feature a center detent. Well over a dozen illuminated push-button switches grace the front panel, and they engage their associated relays with satisfying snicks.


The ISO220's input stage features four switches for selecting the input source, setting the gain range, providing phantom power, and reversing polarity (phase). The ISO220 accommodates microphones, low-impedance line inputs, and high-impedance instruments such as guitars or basses. A stepped gain knob and continuously variable trim knob handles level setting duties. The total amount of gain available is dependent on the input source. Mics get the maximum potential gain, up to +80dB! Line level instruments enjoy up to 50db gain, and lo-impedance instruments up to +60dB total gain.


Whether it's taming rumbles, bringing out the air in the vocals, or carving space in the mix for the lead guitar, EQ is the ticket to well-tailored sound. The ISO220's EQ module features three stages that make up the overall EQ section: a hi-pass and lo-pass filter, a two-band fully parametric EQ, and a two-band shelving filter. Each stage can be switched in or out of the signal path individually, while the All EQ button lets you bypass the entire section at once. The filter section features a hi-pass filter and low-pass filter. The hi-pass filter ranges from 20Hz to 1.6kHz, and the lo-pass filter ranges from 400Hz to 22kHz. This overlap, combined with an 18dB/octave rolloff, not only gives you plenty of freedom to dial out rumbling AC or high-frequency hiss, it also allows you to dial in a narrow band-pass filter for special effects such as the ever-popular "phone voice."


The dual parametric EQs add further dimension with extremely flexible controls. Each band features a continuously variable boost/cut control with center detent, dual-range frequency control, and variable Q. The lower band covers frequencies from 40Hz to 1.2kHz, and higher band ranges from 600Hz to 18kHz.

The EQ module is finished off with high- and low-frequency shelving filters. Each band features a continuously variable level control and stepped rotary switch for selecting the desired frequency range.


Taken as a whole, the EQ stage provided some of the finest and most musical tone shaping controls I've had the pleasure of using.


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The ability to tame wild vocals or flailing bass lines is a critical step in getting great sound, especially when you're interfacing with digital systems. Here, the ISA220 delivers what you need, plus a couple of nice extras.


Ratio is continuously variable from 1.5:1 to 10:1. Threshold is variable from ?28dB to +12db. Attack ranges from 500µS to 25mS, and release varies from 100mS to 7 seconds. Automatic release can be engaged, and it's based on the dynamics of the original signal. While I preferred setting my own release time for vocals, I found the Auto Release control especially useful with acoustic guitar.


Normally, compression comes after EQ so that changes you make to the frequency spectrum don't break the carefully sculpted dynamics. Sometimes, though, that's exactly what you want to do. Some channel strips give you the option of using patch cords to re-route the signal path, but the ISA220 makes it a lot easier - a simple push of the Comp Pre EQ switch places the compression stage before the EQ. Another neat control - unique to the ISA220 - is the Blend function. Often, engineers will split a signal, compress one side of the split, and leave the other untouched. The two signals are then mixed together, giving you both the control of the compressed signal while retaining some of the original dynamics.


Finally, the Makeup control gives you up to +20dB of gain, allowing you to boost levels lost through compression process.


One of the challenges of vocal recording is excess sibilance - those "ssss," "ch," and "ts" sounds that can wreck an otherwise beautiful take. Singers go so far as to change the words of a song to avoid those harsh sounds - "choose" becomes "shoose," for example. You can create a de-esser with many compressors using a sidechain insert and an EQ, but once again, the ISA220 makes this easy. If you're not sure of the frequency range that needs help, press the De-Ess Listen button to solo the de-essing circuit. Then adjust the Freq control to dial in the offending range, set the Threshold to apply more or less de-essing, and get on with the recording session.


Output limiter
The final output is relatively straightforward, with (surprise!) a small enhancement. Output level is adjustable between -60dB and +6dB, giving plenty of range to interface with your recorder or mixer. For more complete control, the output stage features a multiband brick-wall limiter. The threshold is fixed at +22dBu, and the bands are fixed, but I was able to set the ISA220 up so that I was able to drive it hard without overloading my A/D converter.

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As if the rest of the ISA220's features weren't enough, Focusrite gives you the option of adding a 24/96-capable digital output board that includes AES/EBU, S/PDIF, and two-channel optical inputs as well as word clock I/O. With the card installed, the front panel Clock Select, Bit Rate Select, and Ext. Select buttons become active.


In practice
I have a few high-quality pre-amps in my rack, and was interested to hear how the ISA220 stacked up. To try it out, I threw a few sources at it, including vocals, guitar, synth, and bass. I initially set it up with no EQ or compression - just amplification - and was not surprised to hear the clear quality of the sound. Headroom was abundant and distortion was non-existent. In this regard, it was every bit the equal of my other front-end processors. It was when I started adding in EQ and compression that the ISA220 really began to shine. My tube pre is nothing but amplification - no contest. My discrete pre features hi and lo shelving EQ and a variable-mu limiter. Very nice sounding, but no match for the flexibility of the ISA220! I thoroughly enjoyed the full range of EQ options, and how great I could get my mics to sound - whether a large-diaphragm Neumann or the rough-and-ready SM57! Compression was smooth and transparent, and the blend function was a revelation! As for the de-esser, I really took to the way Focusrite has implemented this necessity. It's so incredibly easy to hear, find and fix offending sibilants quickly, and dial out just enough "sss" without sucking out the air in the mix!


Bottom line
I've had a long time to evaluate this unit, and am reluctant to box it up and return it. It has earned a place in my high-end rack, and will someday lend its sound to my control room.