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Alice 538R

Stereo Optical Compressor By Matt Houghton
Published November 2023

Alice 538R

If you’re a fan of Ted Fletcher’s classic optical compressor designs, this one should not disappoint.

I’ve always had a soft spot for Ted Fletcher’s optical compressors. His JoeMeek SC2 became something of a classic ‘character’ compressor for drums, of course, though it deserves praise for more than that one ‘trick’. Most of Ted’s compressor designs over the years have been based to some extent on the same circuit — if it ain’t broke, don’t fix it — and I’ve owned and used quite a few of his compressors and channel strips. I’ve enjoyed them all: classy, yet full of character, and with a little less hiss in the later models than the earliest. So when he sent me his latest creation, the Alice 538R stereo optical compressor, I was very happy to take a look.


The 1U 538R isn’t something you’ll overlook nestling amongst the other gear in your 19‑inch rack: the chassis, which extends 15cm (six inches) behind the rack ears, is painted a distinctive... I’m not quite sure. I could call it ‘muted magenta’, maybe or ‘heather meets lilac’, but certainly it seems a bit more vibrant in the flesh than most images I’ve seen suggest. With the white legends, the warm glow of the meters and the purple power LED, it all comes together pretty nicely.

On the front panel, to the right of a power‑present LED, two moving‑coil meters have a small toggle switch between indicating the left and right channel output levels or the summed stereo output (left) and gain reduction (right). Another toggle instructs the compressor to react to the internal or external side‑chain signal.

The main controls comprise two clusters of knobs, which flank a Char (character) toggle, of which more later. To the right of the switch, the Input knob (marked 1‑10) is a pot to set the level before it hits the compression circuit. Between this and the meters, it’s very easy to set a signal level so that it’s in the right ballpark for compression. The Width control appears to be an M‑S balance pot, and ranges from mono (fully anticlockwise) to 150 percent (fully clockwise), with the balance unaffected at 12 o’clock (detented). The third knob in this trio (again marked 0‑10) sets the Output level. It comes after the meters in the signal path, and is there to set an appropriate level to feed the next device in your chain.

To the left of the switch are four knobs, all continuous pots. Comp sets the amount of compression, by raising the signal going into the compression circuit. Attack runs from Slow (fully anticlockwise) to Fast (clockwise), while Release has the fastest time fully anticlockwise, and Ratio is marked 1.2:1 (very subtle) to 10:1 (effectively limiting). The Char switch toggles between Norm and Dark positions, but the manual’s a little coy about what’s actually happening: a single mention informs us that this “artistically alters the release timing profile”. Finally, a blue On (bypass) button, which some may find a touch too bright, lights when pressed in, in which case the compressor is in circuit; the out (unlit) position is a hard‑wired bypass.

The main analogue I/O are on XLRs, while a TRS jack provides an external side‑chain input.The main analogue I/O are on XLRs, while a TRS jack provides an external side‑chain input.

Inside, the construction is neat and tidy, and almost all components are mounted on a single PCB, with most (though not quite all) being surface‑mount devices. Gain reduction is performed by a pair of Alice‑badged optocells — the higher the signal, the brighter an LED inside this sealed cell glows, increasing the resistance of its light‑dependent resistor. The internal power supply can accept 85‑285 V AC mains at 50/60 Hz through the rear‑panel IEC inlet, and creates ±15V power rails for the internal circuitry. Also on the rear are four XLRs for the analogue I/O and a quarter‑inch TRS jack side‑chain input. The inputs and outputs are transformer balanced, and the shielded transformers (manufactured by OEP, a Carnhill sub‑brand) present input and output impedances of 10kΩ and 100Ω, respectively. The frequency response is within 1dB of flat across the audible band and various other decent‑if‑not‑groundbreaking specs are detailed in the manual. Suffice it to say that with no processing taking place this thing sounds subjectively clean and quiet, and the more you compress the more character is added in terms of harmonic distortion.

As with all optical compressors, the attack, release and even the ratio vary somewhat with the signal level. But an interesting aspect of Ted’s stereo compressors made in the last couple of decades is that the compression is performed not on the left and right channels of a stereo signal but on the Mid and Sides. This eliminates the problems of channel imbalances owing to differences in the dynamic response of opto cells. A potential downside is that it means you cannot used both channels as mono compressors (though you can use one channel in mono if you wish). A bonus is that since M‑S is an intrinsic feature of the compressor design, Ted has taken the opportunity to present the user with the M‑S balance (Width) control.

Both the inputs and outputs are transformer balanced, and the gain reduction is performed by Alice‑branded optical cells.Both the inputs and outputs are transformer balanced, and the gain reduction is performed by Alice‑branded optical cells.

538R In Use

When the 538R arrived, I was working on a rock mix featuring a good range of instruments, including multitrack drums, double‑tracked male lead vocals and stacked backing vocals, electric bass, several electric guitars and a piano. So I inserted the 538R on the master bus and started soloing different sources, just to get a feel for what it had to offer. Setting levels was easy: I could just turn Comp right down, turn Input up until I saw a healthy level on the meters, then set the Output level while watching my audio interface’s meters. Flipping the meters to show gain reduction, I found the controls pretty intuitive, but because of the wide range they offer they could seem a tad sensitive — on some sources where I wanted less ‘character’ I had to spend a little more time than I’d have liked optimising the settings. That said, I could always set things as I wanted.

On a drum bus, I coaxed a characterful, explosive, pumping sound out of this compressor very quickly — the sort of effect that’s great in parallel compression.

On a drum bus, I coaxed a characterful, explosive, pumping sound out of this compressor very quickly — the sort of effect that’s great in parallel compression. There’s no wet/dry mix control here, which some will miss, though I can’t say I did, as I generally prefer to put the parallel processing on its own channel, where I can EQ it and leave the dry level unchanged. Spending more time with the drums, I soon got a feel for the lightness of touch required to achieve more delicate compression; the slightest twist is often all that’s needed, but the knurled metal knobs make this easier than it sounds.

Of course, it’s not all about drums. I often find that bass responds well to optical compression (and vice versa!) and for a while I had a Fletcher‑designed channel strip as my main bass input channel. The 538R didn’t disappoint. It did a decent job of controlling the peaks and making bass parts sound that bit fuller, without being too obvious or losing detail. I could achieve a lovely, almost tape‑like smoothing/gluing effect on the guitar bus, again without things turning to mush. Generally, though, you’ll find that the more delicate or exposed the source and the subtler the result you seek, the fussier you need to be with the controls. It was capable of a lovely result on lead vocals, for example, but the controls tend to interact a bit (largely, I think, because the ratio and time constants vary with the level/amount of compression) and I found I wanted to spend a fair bit of time massaging the Comp, Input and Output knobs to achieve the best result.

The M‑S‑based Width control is an unusual but useful bonus, and a result of the approach Ted Fletcher uses to prevent discrepancies between two channels in his stereo optical compressor designs.The M‑S‑based Width control is an unusual but useful bonus, and a result of the approach Ted Fletcher uses to prevent discrepancies between two channels in his stereo optical compressor designs.The Width control is such a useful feature to have on board, and not just for the drum or mix busses. It can be very effective at bringing up the room ambience or reverb (or for pulling the centre into sharper focus) in any stereo signal, from a piano recording to looped samples, and I enjoyed the immediacy of being able to make those decisions as I tweaked the compressor. By way of example, I loved using the 538R to control some stacked backing vocals that had been panned across the ‘stage’ and fed through a stereo reverb. Feeding both the vocals and their reverb through this thing, the combination of gain reduction and width control smoothed things out beautifully, adding a dash of thickness and bringing up details, while also ‘tucking’ the parts in place around the lead vocal. When trying the same thing with plug‑ins, I could reach the same destination — but nowhere near as quickly.

I get why the Char settings are labelled Normal and Dark: the latter results in what I perceived as a slight dulling of the top end, with perhaps a tiny drop in level too. But really it’s a subtle ‘flick and listen’ thing, and I almost always preferred it in the Normal position. I can’t say I’d miss it were it not here, but it would be harsh to criticise the presence of a feature!


That Ted Fletcher’s compressors aren’t talked about more these days has long puzzled me. I have lots of other nice hardware and software compressors available in my studio, but his designs always seem to offer me something different and I’ve enjoyed every one I’ve used. Perhaps it’s because they’ve been around for so long and haven’t been backed with a big marketing spend? Either way, the Alice 538R is true to its lineage, and it’s well worth checking out. The controls may sometimes seem a tad sensitive, but you soon get a feel for it, and when you do, you’ll almost certainly enjoy what you hear.


  • Classic Ted Fletcher optical compression.
  • Versatile.
  • External side‑chain input.
  • M‑S Width control.


  • Small turns can do big things!


Though built using modern methods, the Alice 538R delivers a compression and sonic character that will be familiar to anyone who’s used Ted Fletcher’s processors before — and very appealing it can be, too!


£1062 including VAT.

Alice Audio +44 (0)1442 863494.


Broadcast Depot +1 305 599 3100.