In a world of retro homages, it’s always refreshing when a manufacturer looks to do something a little different...
As I noted when reviewing their xpector headphone amp and monitor controller in SOS January 2025, German company Elysia aim to develop audio equipment that’s not only of high quality but also has a “certain something”. Well, their latest release, the Class‑A xmax master bus processor, appears to deliver several such certain somethings!
Overview
The xmax is available in three different physical formats that have identical features, liveries, functionality and performance: there’s a 500‑series module, a similar‑looking but standalone Qube version, and a 1U 19‑inch rackmount variant. Being true stereo units, there’s only one set of front‑panel control knobs, and in the case of the rackmount unit that was loaned to me for this review, these are arranged in four groups (Threshold, Control, Gain and Shape), with two placed either side of a central section comprising a backlit logo, three latching button switches and a group of six small LED meters. Each control group comprises three knobs.
This unit’s rear panel carries all the I/O connectors, of course. These comprise a balanced input and output for each channel, presented on both XLR and TRS wired in parallel, and a second balanced TRS output (labelled Ext 2) for each channel. There’s an IEC mains connector, with an on/off switch, a fuse compartment, and 115/230 V voltage selector.
On the rear panel, you’ll find the usual analogue I/O on XLRs and jacks, and a globally compatible IEC power inlet with on/off switch.
While the xmax is designed to receive a left‑right stereo signal at the input, this is immediately encoded into Mid‑Sides (M‑S). The Mid is then split by a variable crossover filter (40‑470 Hz), to create two bands, described as Low and Mid (making it the Mid band of the Mid signal... I wonder if a different name for the band might have been helpful!). The Mid signal’s two bands and the Sides signal each then pass through one of three VCA compressors, each with its own threshold and make‑up gain controls — the threshold controls are the first trio on the left of the rackmount xmax, while the make‑up gains (±12dB) form the first trio to the right of the meters.
After any compression and make‑up gain you apply, the Mid and Low bands are recombined, and the Mid and Sides signals pass through the stereo ±8dB shelving high‑frequency equaliser (whose control is labelled Tone) before everything is decoded for delivery as L‑R stereo to a soft‑clipper stage that can be used to control high‑level transients, and, finally, the output level control.
I’ve discussed the compressor threshold controls already. The adjacent trio of knobs is labelled Control, and the first of them sets the Mid bands’ crossover frequency. The next specifies the release time (10ms to 1.7s), which applies to all three compressors. The third is used to link/unlink the three compressors’ control voltages, and ranges from them acting completely independently to being fully linked. When linked, the loudest control voltage takes precedence — the xmax behaves more like a conventional single‑band VCA compressor, but you can set the band thresholds to determine which parts of the signal are most likely to trigger gain reduction.
Next comes the three buttons, and when active each of these is surrounded by an illuminated LED ring. The first, labelled Hit It!, switches the xmax in and out of hard bypass. Next, Punch changes the compressors’ common ratio from 1:1.45 to 1:2.55. Finally, Lowmo (shorthand for Low Frequency Mono Maker) inserts a fixed 150Hz 12dB/octave high‑pass filter into the Sides signal, to remove low‑frequency content that could cause phase issues in stereo, and ensure the energetic low end is distributed evenly across the L‑R channels.
To the right of the logo are two horizontal rows of LED meters, and it seems to me that their role is probably more to offer visual confirmation of what you think you’re hearing than to assist in processing decisions. Gain reduction for the Mid band and Sides channels of up to 9dB is indicated across seven LEDs on the first two meters of the top row, while the Low band is catered for by the first meter on the bottom row. Second on the lower row comes a soft‑clip limiting level meter (unscaled). Finally, on the right of each row, we have simple two‑LED displays of the Mid and Sides channel levels.
The third control grouping (make‑up gains) I’ve covered, and the final trio of knobs, collectively labelled Shape, contains the controls for the high‑frequency shelving equaliser (Tone), the soft clipper (S‑clip, ranging from min to max), and the output level (±12dB).
The xmax’s signal flow, showing how the three compressors operate separately on the Sides signal, and two different frequency bands of the Mid.
In Use
Once I’d spent a little time getting acquainted with the xmax, I found that a decent starting point was generally to set the three thresholds to give me audible compression with approximately equal amounts of gain reduction on the meters, then to choose a crossover frequency, often using the Low and Mid bands’ gain controls to help judge that, and then auditioning the effect of the 150Hz Lowmo filter.
Setting the release time came next. The attack time for all three xmax compressors is fixed at 10ms, so it’s simply a case of setting the release time to what feels right for the track. If gain reduction reaches 8dB or more, Elysia’s proprietary Auto Fast function automatically shortens the attack time to catch any fast, high‑level transients, but doesn’t affect the release, and once gain reduction drops back below 8dB, the attack time returns to 10ms.
Although billed as a master bus processor, the xmax can be deployed with great success across any stereo bus, stem or subgroup.
Although billed as a master bus processor, the xmax can be deployed with great success across any stereo bus, stem or subgroup, be it drums, acoustic and electric guitars or basses, brass, strings, vocals or any other source that you’ve recorded. The default compression ratio of 1:1.45 is perfect for gentle control, while the steeper slope of the Punch‑activated 1:2.55 ratio is well‑suited to compressing, for example, drums, bass or any other source or track where you want to add intensity and energy into the mix. Increasing the degree of control‑voltage linking is another area to experiment with. As I alluded to above, you can go from having three completely independent compressors at the minimum setting, to fully‑linked compressors at maximum, in which case they function in a similar way to a more conventional VCA bus compressor.
At some point while you’re feeling your way into all this, your ears will start to take over, and you’ll find yourself working intuitively across both the compressor and gain controls balancing the Mid signal’s Mid and Low band levels and the width of the stereo soundfield in response to, and as part of, the changes in compression that you’re making. You’ll discover that you can also use the compressors’ gain controls as tone controls: adjusting the relative levels of the Mid bands obviously shifts the tonal balance overall, but the high‑pass filtered (or unfiltered) Sides signal will also have a different frequency balance, so pushing that up or pulling it down will also affect the overall tone of the stereo signal. Then there’s the additional option of using the shelving Tone control, which acts in tandem on the post‑compressor Mid and Sides signals, to tame or enhance high frequencies all the way up to 20kHz as required.
Sonically, I couldn’t find fault with the xmax. Its <10Hz to 180kHz (‑3dB) bandwidth, THD+N (at 0dBu, 20Hz‑22kHz) of 0.01%, ‑91.3dBu noise floor (20Hz‑22kHz A‑weighted), 112dB dynamic range (20Hz‑22kHz), and maximum input and output levels of +21dBu of +22dB, respectively, are pretty impressive.
The soft‑clip limiter is designed to deal with any short, high‑level transients that might otherwise result in clipping in the A‑D converter that will normally come straight after the xmax in a signal chain. Unlike a classic brickwall limiter, the soft‑clip circuitry is designed to operate more like analogue tape saturation, rounding off the peaks rather than chopping them off hard. Although low levels of saturation, which can boost harmonic content, can make a track seem louder than it actually is, it isn’t something that you really want to be leaning on when mixing or mastering acoustic or classical music recordings.
Nowadays, I see a couple of main roles for a master bus compressor. First, it can be there to add a little more ‘glue’ or cohesion to a mix, or a stereo subgroup, much in the way a lot of people like to use an SSL‑style bus compressor, and perhaps a little sheen and polish with EQ or targeted saturation. The xmax can do all of that if you want it to. Of course even the more assertive of its two ratios is relatively gentle compared with the options on some classic bus compressors, but in this case you have some interesting ways to massage the compressor’s response and the tonality in different directions.
The other role is to optimise the track’s energy distribution and perceived loudness. Mastering tracks to take into account this loudness normalisation is too big a subject to get into in detail here — we’ve explored it in these pages many times before — but it requires a somewhat different approach compared with the peak normalisation I used to use when mastering for vinyl and CD. For streaming, I tend to end up with an integrated loudness of around ‑14LUFS, and always keep peaks below ‑2dBTP. These days, I take care of most of that side of things with plug‑ins inside my DAW, but I’ll often run the track through an analogue mastering compressor or passive EQ for a final touch. It works very well for me. Substituting the xmax for my DAW’s loudness plug‑ins brought a significant change in feel to that part of the process for me, making it more intuitive, and allowing me to achieve a result that I think, although exactly the same in terms of LUFS and peak levels as that through the DAW, sounded better overall; it certainly felt much more creatively satisfying.
X Factor?
Hardware M‑S‑based master bus processors tend to fall into two camps: those that are essentially stereo‑width controls, but perhaps with dedicated facilities for managing the low frequencies in a couple of cases; and rather pricier, more fully featured units equipped as a minimum with compression, EQ and width control, capable of producing superb results, but whose operation is somewhat more complex. Elysia’s new xmax sits somewhere between those extremes. It delivers an impressive bus‑mastering performance, yet has an incredibly intuitive user interface, and can be yours for a price that I believe represents absolutely excellent value for money.
If a hardware M‑S‑based master bus (or any other bus) processor is on your wish list, I highly recommend auditioning the Elysia xmax. If it impresses you as much as it did me, then the hardest choice that you’ll then have to make will be between the three form factors; my personal preference is for this rackmount version but the others have plenty to commend them to.
Alternatives
For a similar price you’ll find good options from SPL and TK Audio, albeit with fewer features. Move higher up the price ladder, and SSL, Wes Audio and Rupert Neve Designs offer more features — but, arguably, slightly less intuitive operation.
Pros
- Capable of great‑sounding results.
- Intuitive operation.
- Excellent value for money.
Cons
- None.
Summary
With this impressive Mid‑Sides‑based processor, optimising a stereo signal’s dynamics, width and perceived loudness is a rewarding, intuitive process.
Information
500‑series version £949. 500‑series version supplied in Elysia Qube chassis £1349. 19‑inch rackmount version £1399. Prices include VAT.
Elysia +49 2157 870 440.
500‑series version $1399. 500‑series version supplied in Elysia Qube chassis $1599. 19‑inch rackmount version $1999.
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