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Grace Design M102

Optical Compressor By Eric James
Published June 2014

Grace Design M102

How much of Grace Design's know-how and revered sound has made it into this unassuming and comparatively low-cost box?

In the early 1990s, Michael Grace began designing and making very pure-sounding microphone preamps. They quickly became noticed by those in the know and a few years later he founded Grace Designs and put his first commercial model, the eight-channel 801 mic preamp, into full production. At the turn of the century I bought the 801R, a remote-controlled version, for my classical location recording business and Grace kindly agreed to modify it to include a pair of high-gain channels that would get the best out of my Royer ribbon mic. I spent the first hour or so after the Grace arrived just looking at it. In a pro-audio world then mainly populated by simple black steel enclosures and ugly plastic boxes it stood out as a beautiful shiny aluminium sculpture, with gently backlit, glowing pink, full-width front-panel metering, and engraved with mysterious cosmic symbols that didn't quite spell out the name Grace. The remote control was not quite as shiny, and lacked the symbols, but was a 'mini me' version in every other respect, including its weight and a lovely sense of crafted solidity. The Grace often drew admiring comments on recording sessions even before we plugged it in. And more of them after we plugged it in! I used the 801 on hundreds of classical sessions for nearly a dozen years and when the recording side of the business was sold off to concentrate fully on mastering and post-production, I set an unrealistic price tag for it, secretly hoping that nobody would buy it! They didn't, and so it is still in daily use in my mastering facility, where it does sterling duty providing pristine make-up gain for passive EQs and adjusting overall gain for the analogue path before returning to the digital domain.

Judging By Appearances

It's because of this history that I was particularly keen to review Grace's more recent M102 compressor. Unfortunately, because in my mind there was something of a natural match between the gorgeous aesthetic of the early 801R's and their superlative purity of sound, my initial impression on unwrapping the M102s from their cartons was basically one of concern. In fact, to be perfectly honest, when I took the first exceedingly

lightweight, rather nondescript little black box out of its hi-tech inflatable packaging, my first thoughts about the M102 were something less than charitable. Grace do still make high-end preamps and monitor controllers, and even headphone amps that win audiophile awards, and although none of these superb pieces are quite as beautiful as the original 801, they're all visually recognisable as its offspring, having inherited a substantial proportion of the original product's aesthetic appeal. That, I'm afraid, cannot be said of the M102.

Before you draw hasty conclusions, though, I should explain that I am on record in these very pages complaining about manufacturers who are chasing the 'retro' money by putting a couple of PCBs in a flimsy pressed-steel box, painting it anything but black, and then suggesting that it has some special character. It would be a bit hypocritical if I let the opposite approach sway me too much, so I just kept reminding myself that this unit costs a fraction of some of Grace's higher-end offerings and only about 10 percent of my original Grace preamp! Although it did take me quite a while to make the mental adjustment, it all ended happily, because the sound of the M102 entirely belies its looks.


The M102 is a mono optical compressor which measures approximately 8.5 inches wide and just over nine deep, taking front and back protrusions into account. There are no rack ears and apparently no provision for adding them, although a threaded hole on the bottom panel is provided via which you can secure the unit to a rack tray. On the back panel there are single XLR balanced input and output connectors, each with parallel quarter-inch jack options, and another quarter-inch socket for stereo-linking and a side-chain input. On the front are four small (half-inch diameter) chromed plastic knobs for controlling threshold (+15 to -15, no other markings, no detents), attack time (3-200ms, with no detent but a centre marking of 150ms), release time (0.3-3 seconds, also with a centrally placed 1s mark) and ratio (1:1 to 12:1, no detent and another centre-ish mark of 4:1). These are flanked by two larger (one-inch) knobs, the leftmost of which controls the input level (-10 to +10, no markings, centre detent) and the rightmost of which governs the output level (-10 to +10, no detents). In addition, there's a gain-reduction meter, which takes the form of a row of LEDs marked 1 to 10, with each LED representing 1dB of gain reduction, and a single peak LED, which glows green when there's at least a -10dBu signal present (or perhaps -15dBu, depending on whether you are consulting the manual or the tech spec sheet!). This changes to red at +20dBu, which is 6dB before the clipping point. Finally, there are two small switches. One activates the stereo link for connecting two M102 units together for stereo operation (more on this below) and side-chain input for inserting an externally EQ'd signal for frequency-sensitive compression. The other activates the whole unit and provides a 'soft' bypass.

In Use

I always try to test review equipment on real-life sessions here at Philosophers Barn Mastering. The M102s are intended primarily for tracking and mixing work but, as our name implies, we no longer do so much of that! I had limited opportunities, then, for testing the M102 on live input sources. But the M102 is all about transparent compression, and there's really no better way to test how it performs in that respect than to use a pair of them on some our stem-mixing and mastering sessions, comparing them with my go-to choice of mastering compressors.

The first project was a jazz programme, with female voice and piano. Originally, I'd been asked only to master this but the mix had been created under less than optimal conditions — so although the internal balances were pretty good there were some other issues that required attention and, as the mix engineer was away and unable to work on it further, we were asked if we could complete the project using the material on a few stems (a double-tracked vocal harmonising with itself and a solo piano), optimising the individual elements as best we could before mastering the result. I'd assumed initially that this would only involve EQ, but when the voice stems arrived it was immediately clear that they also needed a bit of dynamic control in places. The main problem was that they'd been recorded relatively close and relatively dry, so the natural dynamic changes, especially on notes starting a phrase, were being overemphasised by the mic position and a novice mic technique. My usual choice for this kind of work would be the pricier Pendulum OCL2 valve optical compressor, which was designed and built by a classical musician. I've used it to do some very mild and unobtrusive things on a number of sensitive recordings, so I was keen to find out how Grace's solid-state optical compressor would compare.

Label Conscious

I had done some preliminary work on the project with the Pendulum before the Grace arrived, and so already had some working settings that I thought I could simply roughly reproduce on the M102 as a starting point. But although the Pendulum is itself non-switched, and has relatively meagre setting markings on its various controls (which you can get used to pretty quickly), the Grace was quite a way behind even that level of information provision. Consider this: when the first half of the travel of the attack time knob covers a range from 3-150ms, and the second half covers just a further 50ms, where, on an otherwise unmarked dial is, say, 35ms? Similarly, the release range is from .03 seconds to a full 3 seconds, but the first half of the travel covers 0.03-1s, with the second half spanning the further 2 seconds; how do you find, say, 500ms?

The presence of both XLR and jack I/O options should make it easy to plumb the M102 into any studio, and there's also a TRS socket to cater for the summing of the side-chain signal, in order to use a pair of M102s for compression of stereo sources without any unwanted shifting of the phantom centre.The presence of both XLR and jack I/O options should make it easy to plumb the M102 into any studio, and there's also a TRS socket to cater for the summing of the side-chain signal, in order to use a pair of M102s for compression of stereo sources without any unwanted shifting of the phantom centre.The ratio control is similarly configured, but I don't want to labour the point, which is simply that if you depend on knowing more than just very approximately what your compressor parameter settings are, you will not get very much joy out of the Grace M102. For some people, and maybe especially for project-studio users who are still a bit dependent on guidelines (not to mention the sad cases on some boards who take every suggestion to be a recipe to be followed to the letter!) this will be a problem.

Having said all that, it should be noted that the M102 compressor has simply been ported from its original home in the Grace M103 recording channel strip, where it was joined by an EQ section and a mic pre, and in the recording situation, it's more often the case that near enough is good enough, as it's what gets captured that counts. Also, for recall purposes settings can obviously be roughly sketched in a visual way (see, for example, the rapidly expanding range of recall sheets available at

Putting these issues aside, there is absolutely no question at all of the excellent performance and sound quality of the M102. Having abandoned my original plan (and any hope of direct comparison) I dialled in what looked to me to be ball-park similar settings and tweaked by ear. The results were very satisfying. Making full use of the highly responsive gain-reduction metering, it was pretty easy to set the M102 up to be quiescent in all but the loudest passages, but then to exercise smooth control over the problem parts. There's a signature kind of smoothness that you expect from an optical compressor — a sense of mildly increasing action when the threshold is exceeded by more than a margin — and it was there in abundance, and so the vocal immediately began to sound more professional and more pleasant. As I expected from a Grace product, just having the unit in line but inactive seemed to make no easily discernible difference despite there being no hard bypass, and when it was set up in the right way it added only good things. My decision, in the end, was to use the Pendulum for this particular project, but this was not due in any way to a lack of quality results from the M102. It did the job well and unobtrusively. Rather, I felt that the Pendulum, fitted with a decent set of valves, happened to add some other useful qualities (slight bloom and width), which worked well on this material.

Boom For Improvement

I also used the M102 on another jazz project, but this time the main problematic element was the acoustic double bass sound. It had been recorded with a single mic, which I'm guessing was positioned just above the bridge and pointing upwards, because it had a nice mixture of 'woody' bass body and important textural details from the fingerboard. The problem part of sound was a swell on the deeper notes, which added an unwanted boominess and took away from the overall detail and presence of the sound.

The best way to control unruly bass is usually with EQ, but a boominess can be thought of as an arch that swells maybe a tad too late, maybe a tad too much, and which certainly stays around rather too long! The most effective way to control this is actually with a gentle and temporary gain reduction from a compressor, adjusting the attack to allow for the initial 'struck' part of the note to get through, using a somewhat slow release, so that the compression action stays in place to keep the arch from rising. The timing of the release is dependent on the severity of the boom and the beat of the track. Rough starting points can be calculated from the BPM (60,000/BPM = pulse), but the best way to find the right amount is not to use a formula. It's simply to listen: start with a release time you're sure is too slow, so you get over compression (and attenuation) of the body of the note, and then speed it up until the lifting of the compression allows it to be heard but not to dominate. The M102 appeared to have been tailor-made for this job, combining transparent, unobtrusive gain reduction with ease of control.

Stereo Use

Knowing that the M102's origins were within a mono recording channel strip, I'd not really thought too hard about using it as a stereo-programme compressor, and in fact I thought it might be a little unfair to try it like that; it was fairly obviously not going to be its strongest suit. But then I watched the video from the 'showcase' where it was launched (which is now on the Grace web site) and heard Michael Grace tell our very own Hugh Robjohns that it could be used in this way, so I decided to try it out.

For the mastering purposes that are my usual line of work, the general amount of compression used is typically very small. In fact, far more often than not the gain-reduction needles on my units are hardly moving at all. Because of this, I tend to leave the stereo compressors that I use unlinked — I just think it sounds better that way. However, in other stereo applications, such as stereo-bus compression while mixing, the compressor will often be used more assertively. If there's less than, let's say, 1dB of gain reduction, and especially if there is a strong compression-triggering element on just one side of the mix, then it's always best to link the sides so that compression induced anywhere is applied everywhere. (A couple of dB of gain reduction applied to just one side of a full mix is always going to make those compressionFor applications when the setting of attack and release times is better done by ear — such as when tracking — the knobs afford the user a decent degree of control, but as there are no detents or accurate markings, it might be useful to have a recall sheet handy when mixing!For applications when the setting of attack and release times is better done by ear — such as when tracking — the knobs afford the user a decent degree of control, but as there are no detents or accurate markings, it might be useful to have a recall sheet handy when mixing! moments sound pretty odd!)

In order to use the M102 in a stereo configuration, the mono units have to be linked using a simple quarter-inch jack lead, and each unit has to have its side-chain switch set to 'link'. The threshold control of one unit is then set to its highest setting (effectively turning off the compressor's own internal side-chain) and with the side-chain signals now summed, the other unit acts as the overall master controller for setting the threshold and attack and release times. The ratio controls remain entirely separate, a design decision that Grace explain is to enable fine adjustment of the stereo image, which might conceivably be affected by the possibility of "slight, unavoidable variances in the opto-coupling devices”. I didn't notice any such problems at all while I was testing the unit.

Although the pair of M102s sent for review didn't spend a lot of time working as a stereo unit, they worked well enough when used in this way. On complex or detailed material (acoustic jazz or electronica, for example) they didn't sound as open or expensive as the other mastering units I have here — but that would be asking too much of this design, and any device at this price point. Grace are not actively marketing this as a bus compressor, and while it's not likely to be high on the list of anyone shopping specifically for such a tool, it's well worth knowing that if you already own a pair and are happily using them as mono devices, linking them and sticking them on the bus could give you some very decent-sounding results.


In the final analysis, what the M102 looks like is immaterial, and the frustrations it can present to repeatable or recordable fine control will only trouble users who need such things for regular operation. There are plenty of people for whom neither of those will be an issue and what really counts is that in performing the tasks for which it is most obviously designed (transparent compression when recording and mixing solo instruments or voices) the M102 is a flexible, sonically stellar performer. In fact, I can't think of anything comparable at this price.    


  • Sounds as brilliantly transparent as you'd expect a Grace compressor to sound.
  • Stereo-link and side-chain options.
  • Moderate price, given the sonic quality that's on offer.


  • Controls don't allow for accurate setting of time constants.
  • Lightweight construction.


The M102 sounds great, and while corners may have been cut when it comes to aesthetics, this means that the Grace sound is yours for a much more moderate price than you'd expect.


£594 each; matched pair £1218. Prices include VAT.

ASAP Europe +44 (0)20 7231 9661

$685 each.

Grace Design +1 303 823 8100.