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...