HUM Audio Devices N-STRIP

Looking for the ultimate analogue channel strip, cost no object? Then check this out, while the rest of us dream!

Recording engineer and studio equipment designer Krzysztof Tonn opened TONN Studio in Łódź, Poland, back in 1999. Since 2014 this busy studio has also served as the R&D test facility for HUM Audio Devices, a company that Tonn co‑founded with Krzysztof Rudnicki. HUM design and hand‑assemble a range of high‑end boutique ribbon microphones and analogue hardware for recording, mixing and mastering. Tonn aims to deliver “the best possible sound quality together with exceptional creativity, musicality and practical functionality”. If you read our SOS February 2024 review of HUM’s LAAL look‑ahead analogue limiter, you’ll appreciate precisely what he means by that: it’s a no‑compromise, cost‑no‑object design approach.

Black & White Beauties

Their N‑TROPHY mixing console, first demonstrated at 2023’s GearFest UK event at London’s Tileyard Studios, is probably an even better illustration of that philosophy. We’ve not yet had the opportunity to evaluate that console, but HUM recently released the N‑STRIP, a standalone implementation of the N‑TROPHY’s input channel, minus the auxiliary sends and faders. It’s available in two forms: a horizontally mounted pair of channels sitting in a 4U 19‑inch rackmount frame called the N‑CLOSURE 2; and up to six channels vertically mounted in a six‑slot, 11U, 19‑inch rackmount chassis called the N‑CLOSURE 6.

Both N‑STRIP enclosures (the N‑STRIP 2 is pictured) feature an internal linear power supply.

I was sent an N‑CLOSURE 2 for review but, other than the obvious size difference, the two black N‑CLOSURE frames have the same functionality, with an internal linear power supply based around a fully encapsulated toroidal mains transformer. Along with the mains power inlet, all the audio I/O (of which more below) is found on their rear panels.

All the I/O balanced, and is the same as on the console. The main inputs are an XLR input for mic signals, plus a combination XLR/quarter‑inch jack that, with a 10kΩ input impedance, can accept balanced or unbalanced line signals. There’s also a dedicated XLR tape input, intended primarily for a DAW/tape machine playback signal, but if using the N‑STRIP simply as a luxury ‘front end’ it could equally well serve as an alternative line input. Further balanced XLRs are used for the line‑level insert send/return loop, and for the Key 1 and Key 2 inputs to the built‑in optical compressor’s side‑chain circuit. The main output, again on XLR, is marked Dir Out, and can be switched on the front panel to be immediately post preamp or after all of the processing.

With just three exceptions — the mechanical VU meter at the top of the strip, the red preamp gain knob just below it, and the phantom power indicator — the colour scheme is entirely monochrome. The immense configurability of each 7cm‑wide channel means that a huge amount of information has had to be accommodated around the various toggle switches and machined aluminium knobs. Thankfully, the precision, clarity and legibility of the white legending is of a quality I’ve not previously encountered on any console. There’s similar attention to detail throughout, in fact. For example, both frames are equipped with a locking on/off toggle switch — a simple and effective solution to the age‑old problem of accidental on/off switching that I’ve not seen before.

The N‑STRIP enclosures feature the same I/O as the channels on the N‑TROPHY console.

Preamp & Processing

There’s an immense amount of control at your fingertips, and while that inevitably makes the panel somewhat busy‑looking at first glance, it’s all very clearly labelled and soon becomes intuitive.The N‑STRIP’s circuitry is fully discrete. It features only full‑size, through‑hole components and, to ensure the highest audio quality, an audio path that’s been designed to be as short as possible. The transformerless, Class‑A preamp is based on Deane Jensen’s JE‑990 discrete op‑amp. Jensen’s design took full advantage of the low noise and matching characteristics of the National Semiconductor LM394 Supermatch NPN pair, but that’s been discontinued, so Tonn’s version replaces them with the even lower‑noise Analog Devices SSM212 dual‑matched NPN transistor.

The preamp stage itself is transformerless and allows you to capture a very clean sound, but each channel also possesses a switchable, custom‑made inter‑stage transformer that means the N‑STRIP can deliver analogue warmth and weight when that’s desirable. There’s also a separate two‑part THD saturation stage that can be used to apply harmonic distortion.

Yet another ‘coloration’ option is found in the compressor/limiter. It’s an optical compressor, but with a valve‑based make‑up gain stage, and you can bypass the gain reduction if you wish — leaving you with the option of driving the valve circuitry to access its flavour of harmonic distortion. And in another example of HUM’s obsessive attention to detail, you’re able to switch off the valve when you’re not using it, so as to increase its life. The valve in question is a hand‑selected and precision‑measured NOS Soviet‑era 6N23P (ECC88 equivalent) dual triode. One of the reasons that this model was chosen is that it can run well on a very low plate voltage — in the N‑STRIP, it’s set at +48V — and I’m told that HUM keep a very large stock of these valves, so sourcing replacements shouldn’t be a problem.

Although based on a photocell, the N‑STRIP compressor’s gain cell uses a voltage divider to control the level of the signal passing through it, and rather than act directly on the signal the photocell forms one of the legs of that divider. This gain‑cell topology is designed to provide better high‑frequency linearity across the gain‑reduction range. In other words, it means there’s less loss of level in the high frequencies during heavy compression. The side‑chain circuitry utilises a full‑wave bridge rectifier to produce the control signal, and two side‑chain control signals can be connected simultaneously, using the external Key 1 and 2 inputs mentioned earlier — these are selected using front‑panel controls.

There’s also a mastering‑grade equaliser on each channel, comprising both variable high‑pass and low‑pass filters, and a versatile six‑band passive equaliser. The six bands are grouped in three pairs, with each pair having two identical frequency selectors, one associated with a boost‑only control, and the other with a similar cut‑only control. Each band operates with a broad (6dB/octave) slope, so the bands enjoy considerable overlap. The control knobs in this section are rotary switches, which facilitate easy and repeatable recall of settings, and enable HUM to perfectly match the EQ characteristics and phase response across multiple channels during manufacture.

Control Freakery

While the preamp and processing stages are easy to grasp conceptually, the N‑STRIP features more channel configuration options and toggle switches than I’ve met in one place before! So it can take some time to get your bearings, and longer still before operation becomes second nature. It’s also quite a lot to describe on the page but, I think, necessary if you’re to fully appreciate how the N‑STRIP might work in your studio. (Though arranged right to left in the review unit, I’ll describe them top to bottom, as if the channel were installed in the console.)

Starting in the preamp section, the red aluminium knob accesses 10‑65 dB of gain. You’ll also find a switch here for 48V phantom power, and as you switch this the channel mutes for a second or so to protect your monitors. Further switches invert the signal polarity, select the preamp source (mic/off/line), set the tape input gain (0, +6 or +12 dB), engage/bypass the transformer, and set the preamp output and tape input routing.

Immediately below the preamp comes the THD saturation section. A six‑position switch selects the distortion type (germanium or silicon diode‑based asymmetric distortion, soft, medium or hard symmetrical distortion, or off), while a THD level control (1‑10) determines the amount of distortion. Below are controls for the insert loop (on/off switch, and a dry/wet control that allows parallel processing of the insert return; a rare and handy feature that must make the console a joy to work with!) and, on their right, a position selector for the direct output, along with its trim control (0 to ‑20 dB) and on/off switch.

Next, we come to two six‑position rotary switches. With one, you can reorder the three post‑preamp sections (insert, compressor and EQ) in any sequence you wish. The other specifies what’s indicated on the meter — the options are the signal level at the preamp or tape input, at the channel output, or post EQ or compressor, as well as gain‑reduction.

The toggle switches beneath all this relate to the compressor. One selects the side‑chain mode, which can be internal, external or an L‑R link of neighbouring odd/even channels. Another switches between Key inputs 1 and 2. The opposite toggles engage a high‑pass filter in the side‑chain, set its corner frequency (60 or 200 Hz), and switch the dry/wet blend control that sits below in and out of circuit.

As well as the on/off toggle switch, which doubles as the ‘valve off’ control, the compressor has three further knobs in this section. One is a Type control, and this morphs the compressor’s attack and release times seamlessly between a slow, glue‑y compression and fast, FET‑like limiting. The threshold control is scaled 1‑10, and increases both the compression level and the ratio as you turn it clockwise. The final knob is a make‑up gain control (0‑10 dB).

As I mentioned, the EQ controls are all rotary switches and these occupy the remaining half of the control panel. In the filter department, one position is off, with the others setting the corner frequency. For the high‑pass filter this can be 25, 50, 100, 150 or 330 Hz, and for the low‑pass the options are 3.3, 5, 10, 15 and 20 kHz. The main EQ bands each have 12‑position switches for the gain or cut (of up to a Spinal Tap‑esque 11dB, in 1dB increments). The HF bands’ frequencies can be set, independently for the cut and the boost, to 5.6, 8.2, 10, 12, 16 or 24 kHz. For the mid it 330 or 560 Hz, or 1, 2.2, 3.3 or 4.7 kHz, and for the LF bands it’s 20, 50, 80, 100, 150 or 220 Hz. The mid band has a peak response, whilst the boosts and cuts in the HF and LF bands can be switched individually between shelf and peak responses, using the toggle switches that sit beneath the knobs. The final control in this section, and for the N‑STRIP as a whole, is the global EQ on/off switch.

Operation

Because it offers so many options, the N‑STRIP required me to think more deeply than usual about what I wanted to achieve. But that’s no bad thing in my book and, complex though all this at first appears, once I’d acquainted myself with the basic routing and switching options, I soon felt at home — in fact, I’d say that after my initial orientation sessions, the N‑STRIP provided me with an extremely well‑thought‑out, logical and, importantly, speedy workflow.

The N‑CLOSURE 6 can host up to six N‑STRIP channels.And once in that happy position, tracking with the two‑strip N‑CLOSURE 2 became a more involving and rewarding process than with most channel strips, because there are so many directly controllable sonic options. The ability to switch the insert/compressor/equaliser routing to any of its six options almost instantly, whilst also being able to tweak (almost simultaneously!) the compressor and EQ settings, or any other control, delivers huge operational and artistic benefits.

The optical compressor is probably the cleanest‑sounding and easiest‑to‑use compressor/limiter that I’ve yet encountered. All I had to do was to turn the type and threshold controls until I heard what I wanted. It’s as capable of keeping vocals or acoustic guitars gently (or not so gently!) in their place as it is of clamping down on a drum stem. OK, so other compressors may offer you a more granular level of control, but the N‑STRIP’s compressor is nonetheless an extremely effective processor that’s more than capable of handling almost all my compression needs.

The passive EQ is an absolute joy to use too. Once I’d started using it and my ears had understood what it was capable of, operation quickly became intuitive — despite the sheer number of boost/cut/frequency options on offer. You can dial in pretty complex EQ curves with this EQ, meaning you can sculpt sounds with precision, but it also somehow allows the dynamics and space in a source to shine through, seemingly untouched.

Should pristine clarity not be your goal, though, the N‑STRIP offers generous options for adding character. At the beginning of the chain, the transformer can be switched into circuit to add both warmth and weight. The THD saturation section offers more controllable distortion, allowing you to generate additional harmonics to give a source a grittier edge or a brighter and more forward feel, courtesy of its germanium and silicon diode‑based asymmetrical clipping options. Alternatively, the symmetrical clipping facility can deliver saturation that’s more akin to ‘pushed’ or overloaded analogue tape. Add the compressor’s valve stage into this equation and, overall, you have pretty much instant access to an impressive range of sonic textures, from subtle to extreme, and suitable for vocals, guitars, bass, drums... you name it.

Happy N‑ding?

While it’s great that the N‑STRIP is positively dripping with features and options, its greatest strength is undoubtedly its stellar audio quality. To my ears, it can deliver detailed, dynamically precise and nuanced results at a level of performance that’s limited only by the quality of the mic being used and the source it’s capturing. The compressor produced superb results on every source I auditioned. As a sound‑sculpting tool, the passive equaliser proved intuitive, subtle and powerful, in equal measure. The saturation section provides an extremely effective way of adding texture to a track. The mix control for the insert is a real bonus, and the ability to sequence these sections as you wish makes the whole thing so versatile.

Personally, I can’t think of any channel strip that’s more desirable than the N‑STRIP.

Where does this leave us? Well, personally, I can’t think of any channel strip that’s more desirable than the N‑STRIP. Of course, quality like this costs, and while even the ‘basic’ two‑channel N‑CLOSURE 2 offers you a huge amount of functionality, this gorgeous channel strip will, sadly, be out of reach for most of us. But for those whose work profile and professional reputation demand and depend on the very highest levels of audio quality, there’s a heck of a lot to commend it. So I’d urge them to audition the N‑STRIP — and if money really is no object, perhaps even the full N‑TROPHY console — at the earliest opportunity.