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Focusrite Green 4 & Green 5

Dual Compressor/Limiter & Channel Strip By Paul White
Published July 1997

Focusrite's new Green processors are enough to make anyone envious, as Paul White discovered when he had to give them back!

Over the past few months, we've reviewed several processors from the Focusrite Green range, so I'll spare you all the obvious jokes about the front‑panel appearance. These two new units are based on the circuitry used in previous Green processors. The compressor/limiter is a fully featured, dual‑channel device for line‑level operation; the channel strip combines a mic/line/instrument input stage with EQ, compression and an expander/gate. Like the other Green units, these two feature transformerless input and output stages and the distinctive sculpted front‑panel styling. In fact, the case is moulded in one piece using aircraft‑grade aluminium, and the green front panel and circuit board sub‑assembly are fitted via the rear of the case. The mains voltage may be switched from 240V to 120V by means of a recessed slide switch, just in case you were thinking of taking one on holiday.

Dual Compressor Limiter

Unlike many compressor/limiters, the Green version includes separate compressor and limiter sections, each with its own threshold controls. Both operate on the same class‑A VCA, and stereo linking is implemented for applications such as mix or stereo subgroup processing. The audio inputs and outputs are on balanced XLRs with switchable +4/‑10 operating levels; according to the manual, a balanced jack version is also available.

In the Green units that combine several processor sections, the compressor tends to be somewhat simplified, but this one has five rotary controls, plus switches for the selection of soft or hard‑knee operation, variable‑frequency high‑ and low‑pass side‑chain filters, bypass, and an auto‑release mode. All the buttons on the Green range have integral status LEDs. The filters cover the ranges 15Hz‑10kHz and 65Hz‑25kHz, and may be used for frequency‑conscious applications, such as de‑essing. Because the filters are only in the side‑chain path, they don't affect the quality of the audio being processed, only the way in which the compressor responds.

Auto release responds to the dynamics of the input signal in such a way that the more it exceeds the threshold, the longer the release time. All the rotary controls are standard compressor issue: threshold, ratio (1:1 to 10:1), make‑up gain, attack and release. Two further rotary controls are provided for the limiter, to control the threshold level and release time, but, interestingly, there's also a Look Ahead button. This introduces a very short delay (based on analogue circuitry) into the compressor's audio path, but doesn't delay the limiter's side‑chain, enabling it to respond to peaks fractionally before they arrive. In digital recording applications where clipping is completely unacceptable, this can be a very useful safeguard — but, for most routine jobs, the manual suggests that you leave Look Ahead switched off, as it reduces the audio bandwidth to 35kHz. Limiter operation is signalled by a red status LED; the compressor has a 10‑section gain‑reduction meter LED display.

Gain Change buttons in the central Link section allow the meters to be switched from monitoring gain reduction to monitoring the input signal level, whereas Link ties both channels' side‑chain together for consistent stereo tracking, in which case the left‑channel controls act as masters. However, the Link button doesn't affect the setting of the Filter or Look Ahead buttons, so these should be matched manually.

In Use

Not only does this compressor sound very nice, it's also surprisingly flexible, partly due to the unusual soft‑knee characteristic. Most soft‑knee compressors come in gradually and then level out, but in this circuit, if you drive it hard enough, you reach a point where the curve folds back on itself — the higher the input signal, the lower the output signal becomes. This is great for those vintage pumping effects where the cymbals actually increase in volume as they decay, and it's also stunningly good for guitar. By choosing the appropriate settings, you can make the available effects range from near‑perfect transparency to overtly effected — but if you want a simple life, the Auto release will work on most types of signal. One particularly impressive result is that the vocals can be evened up without sounding as though the singer is moving back and forth in relation to the microphone.

It's not until you use a good EQ that you realise just how much cheap EQs screw up your sound!

The inclusion of side‑chain filtering also makes it possible to process complex material more successfully, by preventing certain parts of the spectrum from dominating the proceedings. For example, in very rhythmic music the bass tends to control the compressor, but by setting the low filter at between 100 and 200Hz, you can prevent this. For de‑essing, you simply have to bracket the offending frequency range, usually between 2 and 8kHz.

The Green limiter is a valuable ally, especially when you're recording digitally. Even with Look Ahead switched off, the limiter was fast enough for any normal job, and also nicely unobtrusive, and even when the threshold was set way too low, the limiter sounded no more harsh than many compressors I've heard: deliberate over‑limiting can actually work rather well when you need a more creative effect.

Channel Strip

The Channel Strip is such a logical product that I'm surprised it wasn't introduced into the line‑up earlier. Essentially, it provides a one‑box solution to getting mic‑, line‑ or instrument‑level signals into a recorder without the need for a mixer. This is recognised as one of the cleanest ways to record, and many professionals use this method whenever possible. In addition to one of Focusrite's super mic amps, based on the Linear Technologies LT1028 mic amp chip, the Channel Strip incorporates high‑ and low‑pass filters, a 4‑band sweep EQ with switchable mid‑range Q, an expander/gate and a compressor. Though ideally suited to recording vocals, the Channel Strip is also useful for high‑impedance instruments, such as electric guitar or bass, and for re‑processing line‑level signals that have already been recorded. An Instrument/Line jack is on the rear panel, along with a Hi Z/Line selector button; there are also dedicated XLRs for the line and mic inputs. A Link jack enables two units to be made to track for stereo applications, and there's an external key input for the gate, which has its on/off button on the rear panel. I can imagine these rear‑panel switches being awkward in some situations, but there really is nowhere left to put them on the front panel.

In addition to Mic Gain, Input Trim and Output Fader (Level) controls, there are buttons for 48V phantom power and phase reverse. A red LED shows when the high‑impedance instrument line input is selected, and you get Mic/Line selection by turning the switched Mic gain control fully anticlockwise. There's no high‑pass filter or mute as there is in the dedicated mic preamp, and, because of the high headroom provided, there's no need for a pad switch. A 10‑section meter monitors the signal level, post the input Trim control, but it may also be used to indicate the compressor gain reduction and expander/gate operation.

At first glance, the EQ section looks pretty busy, but that's mainly due to the inclusion of the high‑ and low‑pass filters. These cover the same frequency range as the ones in the compressor, and may be switched into the audio path or the side‑chain. When Side Chain is set, the filters appear in the gate side‑chain if Key is selected; otherwise they appear in the compressor side‑chain, for de‑essing and so on. The remaining EQ is dedicated to the main signal path and comprises variable‑frequency high‑ and low‑shelving filters, plus two swept mids with switches to sharpen up the Q for more 'surgical' applications. Like the EQ on other Green products, the EQ here has a very wide range, with the low section sweepable between 30Hz and 480Hz , and the high shelving filter from 2.5‑18kHz. Even the low mid extends right down into the bass, with a 40Hz‑1.2kHz span, and the upper mid goes from 600Hz right up to a bat‑sizzling 18kHz, all with a ±18dB range. Twin Fine buttons select the narrower Q option, while bypass buttons are fitted for both the filters and the EQ.

You're quite likely to hear details in the sound of your instrument that you never realised were there before.

Moving into the expander/gate section reveals a simple two‑control system for Threshold and Release, with a further button to switch from gating to expansion. There's also a gate bypass button and a Fast switch for use with percussive sounds. Interestingly, the gate circuit side‑chain uses discrete transistors, and when an external key signal is connected and the unit switched to Key (on the rear panel), the Ext status LED lights. Selecting the Key button on the front panel puts the high‑ and low‑pass filters into the gate side‑chain, while 'To Meter' displays the expander/gate gain reduction on the red LEDs of the bargraph and compressor gain reduction on the amber LEDs.

Finally comes the compressor, once again based around a class‑A VCA, but with rather simpler controls than the dedicated compressor/limiter. Essentially, the user has control over Threshold, Ratio, Release and make‑up gain; the attack‑time control is reduced to a single Fast button and the release can be switched to Auto. An overload LED warns of clipping at the output. De‑essing can be achieved if you commandeer the filters.


It's pretty hard to fault the Channel Strip on performance, though I did find having the Key and Inst switches on the back panel a little awkward. I also found that, unless the unit was above eye‑level, it was difficult to see the legending — it's hidden either by the edge of the front panel or by the buttons, but then I don't suppose that this would take getting much used to.

Used as a mic preamp, the unit gives a front end that's just as clean and transparent as it is on the other units in the series, and I have to concede that this is an extremely nice‑sounding mic amp. When switched to Instrument, the unit becomes the ultimate DI box, and you're quite likely to hear details in the sound of your instrument that you never realised were there before. As far as I can tell, the EQ section is based on the circuitry used in the Focus EQ, and this has the wonderful ability to let you re‑balance different parts of the audio spectrum without introducing unnatural or harsh artifacts. It's not until you use a good EQ that you realise just how much cheap EQs screw up your sound! Having the narrow Q settings is great for notching out rogue frequencies, and the high‑ and low‑pass filters are good for 'bracketing' sounds to exclude unwanted lows or highs, without affecting what goes on in the middle.

Expander gates are rarely exciting, but this one is easy to set up and smooth in operation, and has a useful display if the To Meter button is pressed. Having the expansion option is good for situations in which you want the gating to be as subtle as possible, and the compressor section that follows is equally friendly. Though there aren't many controls to play with, the compressor works fine on just about any type of programme material and, used in moderation, can sound extremely transparent. Again, cheap compressors may keep the levels under control but they often play havoc with the tonality. No trouble on that front here, but if you crank up the ratio and bring down the threshold, you can still get a nice snappy bass or guitar tone with as much or as little pumping as you require.


Both these units are worthy and logical additions to the Focusrite Green range, and both display the attention to circuit‑design detail that makes Focusrite a world leader in analogue signal processing. As far as the cosmetics go, you either like them or you don't, but what concerns me more is the small, easily obscured legending. As stated earlier, you do soon learn where the controls are, but unless you get close up and read the dials, there are no real visual clues.

The Channel Strip is the ideal solution for anyone wanting to record directly to a hard disk recorder, modular digital multitrack or open‑reel analogue machine, and the choice of mic, line and high‑Z instrument inputs makes it very flexible indeed. The dual compressor may only do one job, but it does it beautifully, with plenty of control range and flexibility. The limiter section works extremely well; though Focusrite excel at transparent compression, this one sounds great when worked hard too.

The Green range is the budget baby of the Focusrite range, but there is no compromise in circuit design. As a consequence, the units aren't actually cheap; but if you've been recording for any length of time, you'll appreciate the advantages of spending that little bit extra on certain pieces of key equipment.


  • Classic Focusrite performance and transparency.
  • Easy to set up.
  • Channel Strip is particularly versatile, as it can double as the ultimate DI box.


  • Legending small, and sometimes obscured by the controls unless you're looking straight on.


Even though this is a budget range, it isn't cheap, but the quality of processing is beyond reproach. The Channel Strip is my favourite so far, as it has so many applications, in both recording and mixing.