MCAudioLab LUNA.5K

High‑quality through‑hole components are used throughout.

More than just a Mid‑Sides widener, the intriguing, all‑analogue LUNA.5K offers you control over front‑to‑back depth.

I was shocked to realise that it’s been 13 years since I reviewed MCAudioLab’s TP1tp single‑channel valve microphone preamp (SOS May 2011). Since those early days, founder Manuel Curcuruto’s company have relocated to Poland, and expanded their all‑analogue 19‑inch rackmount and 500‑series product ranges, which now cover the core studio requirements such as microphone preamplifiers, equalisers and compressors. There are also three less conventional signal processors, including MCAudioLab’s latest 500‑series product, the dual‑slot LUNA.5K.

LUNA Exploration

MCAudioLab describe the LUNA.5K as an “analogue ambient processor”. A derivative of the company’s 2013 (and still in production) rackmount LUNA Vari‑Amb Processor, it’s a fully analogue, Class‑A, stereo device that features the same innovative approach to enhancing the ‘ambience’ in a stereo signal. Naturally, MCAudioLab aren’t keen to give away everything about how this clever process works. But, in essence, as well as encoding the incoming stereo signal into M‑S it runs through the company’s proprietary Analog Ambient Processor (AAP), a complex analogue audio matrix that derives two additional, parallel ‘layers’ that, in the LUNA.5K, are called Foreground (FRG) and Background (BKG). Both layers have individual three‑band EQ and level controls that govern the tonality and amount of each being mixed into the M‑S matrix within the AAP, before the decoded and processed stereo signal appears at the device’s outputs.

Since the FRG signal is phase‑coherent, increasing its level will result in the phantom centre of a stereo image sounding more detailed and more present, without changing the level of the (unprocessed) Mid signal, or its balance with the Sides. Similarly, any increase in the level of the BKG signal, which is not phase coherent, won’t change the level of the (unprocessed) Sides signal or alter its relationship with the Mid. Using the BKG layer to widen the stereo image cleverly negates the risk of creating the ‘hole in the middle’ that can often be perceived when simply boosting the Sides signal relative to the Mid.

The LUNA.5K’s two‑column, five‑knob control layout (BKG on the left, FRG on the right) is slightly unusual, in that both three‑band EQs have the lowest frequency at the top and highest at the bottom. Under the EQ section, in their respective columns, you’ll find the level controls for the BKG and FRG signals. The fifth control in the FRG column is a Width control that acts alongside the BKG signal to further expand or contract the width of the stereo soundfield. Opposite, in the FRG column, is the LUNA.5K ’s output level control. Between the two control columns is a four‑LED stereo level meter that displays signal levels scaled from ‘sgn’ (signal present), through ‑6dB and 0dB to Over. Below that lies the bypass button and its illuminated‑when‑bypassed status LED. Internally, the LUNA.5K employs high‑quality components, all through‑hole types and elegantly laid out across two channel boards, both of which exhibit the excellent build quality you’d hope for from a small, boutique manufacturer such as MCAudioLab.

To The Fore

With its maximum input and output levels of +20dBu and frequency bandwidth of 20Hz to 22kHz, the LUNA.5K integrated into my studio setup without any issues. Although the LUNA.5K operates in Class A, I didn’t find heat to be an issue, even in the middle of a fully‑populated six‑slot Radial Workhorse 500‑series enclosure that had been running for most of the day. As you might surmise from the simplicity of its controls, operating the LUNA.5K is intuitive, but if you’re as accustomed as I am to EQ layouts where the HF rather than the LF control knob sits at the top, you might find yourself occasionally wondering why adjusting the treble is changing the bass, and vice versa!

With the FRG layer, I always succeeded in creating a sense of ‘focus’ within the stereo soundfield.

A large part of my personal learning curve with the LUNA.5K simply entailed listening to its effect on a variety of stereo stems and mixes, in order to understand just what the unit can and cannot do. With the FRG layer, I always succeeded in creating a sense of ‘focus’ within the stereo soundfield, bringing forward elements that I perceived to be in the ‘centre’. I found the results from the BKG layer more variable, largely because these depend on the amount of L‑R phase difference in the original stereo signal. Mixes with substantial phase differences from, for example, time‑based spatial effects tend to allow you to significantly alter the width of the soundfield using the BKG layers, and vice versa.

For situations in which the lack of significant phase differences means that the BKG can’t deliver the results that you hoped for, or if you want to go further than the best that it can do, then you can turn to the Width level control. This is a more conventional Sides level control and, as you’d expect, increasing the Sides level results in the perception of greater stereo width. But, importantly, the presence of both the FRG and BKG controls can still help you avoid the ‘hole’ in the phantom centre that I discussed earlier, even if you push the Width control to its limits.

The LUNA.5K ’s EQ section employs Baxandall shelves for the high and low bands, and a peaking response in the midrange. Even though it’s more suited to allowing you to sculpt the tonality of the layers, rather than to carry out major surgery, it’s effective. I found that using the LUNA.5K ’s EQ to accentuate the main frequency area of an instrument or vocal that I wanted to bring forward in the FRG layer, and to attenuate the same frequencies somewhat in the BKG, was often the key to coaxing out what I wanted to hear from the LUNA.5K.

Another effect — and potential advantage — of using the FRG layer to bring forward and increase the central focus of a track is that this can create a sense of greater front‑to‑back separation. In other words, it can changing your perception of the depth of the stereo soundfield. I’ve long used very short delays, both on sources and on sends to analogue reverbs (and pre‑delays on digital and plug‑in reverbs) to create an illusion of depth in my mixes, but the LUNA.5K is a more elegant means of achieving a similar effect.

Finally, out of interest more than anything else (because it isn’t my area of expertise), I ran several recordings of classical orchestras, chamber orchestras and small ensembles (with and without soloists) through the LUNA.5K. The results of this experiment suggest that MCAudioLab’s ambience processing could well have much to offer recordists who work in this area with multiple microphones, either in arrays and/or as spot mics.

Moonstruck?

The LUNA.5K may not be particularly inexpensive for a 500‑series processor but, whether processing stereo stems or mixes, it’s more than capable of altering your perception of the depth and width of a stereo soundfield, by bringing forward and increasing the focus on central sources using the FRG control, or by increasing the apparent overall width by utilising the BKG and Width controls. And it’s the only 500‑series module I know of that can manipulate the apparent width, depth and central focus of a stereo signal so swiftly and easily. What’s more, it delivers a superb overall audio performance.

Of course, your personal view of the LUNA.5K’s worth will depend entirely on whether you need access to what it can achieve. But it could well prove priceless to some. Personally, before I began this review, I didn’t think I’d need a LUNA.5K — but having heard what it can do, I’m persuaded that I do! If you’re involved in tracking, mixing, remixing and/or mastering, and are attracted by the prospect of an analogue stereo 500‑series processor that gives you the ability to swiftly and easily remodel a stereo soundfield, you really should audition MCAudioLab’s LUNA.5K. In my experience, there’s nothing quite like it.