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Audient Black Series

Modular Rackmount Processors By Hugh Robjohns
Published May 2008

Audient Black Series

If you want quality outboard in a compact frame, modular systems are the way to go. Find out how Audient's offering compares with the rest.

It seems slightly odd in this age of computer plug-ins that there should still be interest in rackmount hardware for audio processing — but the demand is definitely still very strong, as the market clearly shows. In particular, modular racks of processors are becoming highly fashionable once again, with offerings from the likes of SSL (the X-Rack), Tonelux (the V8 Roadster) API (the Lunchbox), and other variations on the theme, such as the Rupert Neve Designs' Portico system. The latest addition to this genre is Audient's Black Series: a range of very high-quality and intriguingly innovative modules that can be mixed and matched to suit the user's requirements.

Audient's designer, Dave Dearden, has taken a fresh approach to the design of these 'Dark Art' modules, all of which are quirky and interesting in various ways. With a long career that has included working in some of the best studios around the world, Dave has acquired a wealth of experience of classic outboard processors — how they were designed, how they work, how they sound, and why engineers and producers like the sounds they make. Armed with that knowledge, he has designed the various Black-series modules not to emulate any specific classic outboard devices, but to be capable of delivering the kinds of sonic signatures that made classic outboard classic in the first place!

The bottom line is that the Black Series is all about the sound and the way the sound can be controlled, rather than yet another attempt to recreate the past. Having said that, of course there are a lot of familiar tried-and-tested design touches in the Black series, starting with the transformer-coupled, discrete, class-A circuitry, used throughout almost all the modules. The 4U frame size chosen for the Black series also affords the advantage of allowing slightly larger front panels than many competing products — which means there's more space for extra bells and whistles.

Amongst the unusual features on offer, the mic preamp includes Audient's proprietary 'HMX' harmonics control, which allows the user to determine how much harmonic distortion and colour is introduced to the signal. The equaliser module features an Overtone function adding some harmonic coloration, and a Glo mode that compresses the bass content to make it fuller and tighter. If that's not enough, there is also a Tilt switch to introduce a subtle lightening or darkening of the overall tone. The compressor module is an optical design with an 'overcomp' mode to introduce pre-compression and a dual-mode side chain, combining the best characteristics of both RMS and peak sensing.

Finally, the Black Series includes an A-D converter module that provides up to 24-bit, 192kHz conversion. The unusual aspect of this module is that there's nothing unusual about it — other than the superb quality, of course! In general terms, the technical specifications for all the modules are as you would expect of Audient products, and even seem to be rather conservatively rated in some cases.

Rack Frame

The heart of the Black Series is, of course, the frame that supports the individual modules. The BR10 rack can accommodate up to 10 modules in pretty much any order the user requires. The 4U rack extends about 250mm behind the rack ears, and the separate PSU takes another 2U of rack space. Neither get particularly hot, so you could mount the PSU directly below the rack if you needed to.

The power supply is a substantial unit, with just an on-off switch on the front panel, and five yellow LEDs to indicate the correct operation of the various DC supply voltages: ±48V, ±18V and +12V. The rear panel carries a fused IEC mains inlet and an input voltage selection switch (230 or 115V AC), while the screened 1.5m DC output cable is permanently attached to the PSU, and terminates in a huge, eight-pole Neutrik Speakon connector. Although intended for complex speaker arrays, this connector can easily handle the voltage and current demands, and provides a secure locking connection, making it ideal for this application.

The back panel of the main BR10 rack unit carries a lot of connectors, since each of the 10 module slots is provided with three XLR connectors. These provide two inputs (A and B) and one output (C) — although the actual implementation varies with the different modules, as I'll explain later. A pair of 25-pin D-sub connectors is also provided, and these duplicate the 'B' inputs and 'C' outputs to make connection with a recorder or console easier. However, as they use the ubiquitous Tascam wiring protocol they can only accommodate the first eight inputs and outputs, respectively.

There's also a Speakon power connector, of course, and the last socket is a BNC that provides word-clock in or out (depending on module configuration) and has an associated 75Ω termination switch. If the Black-series master digital clock module is not installed, this socket serves as an external word-clock input feeding any installed A-D converters (or future digital modules, potentially) that are in the rack. However, if Audient's master clock module is installed, the BNC provides its own word-clock output for use in synchronising external equipment.

A small graphic on the rear panel reminds the user how the 'A', 'B' and 'C' sockets relate to the various module types. Installing or removing modules is very simple, requiring the removal of just two front-panel screws. The modules locate in slides and slot into the back plane via industry-standard DIN 41612 connectors. However, the manual contains warnings about the modules being sensitive to static, so the user is advised to take normal handling precautions.

The Black-series rack supplied for review was fitted with two preamps, two equalisers, two compressors, the A-D converter module, and a master-clock module — leaving two slots free. The audio is not distributed within the frame in the same way as with many other rack units. Instead, modules must be linked manually in the required order, using short XLR cables (not supplied) between the various rear-panel connectors.

Preamp Module

Like all the Black Series modules, the preamp is well laid out, and easy to understand, given the white labels on a black panel. Starting at the top, two illuminated push-buttons select +48V phantom power (blue) and a polarity inversion (switched via a relay). Next is a switched, rotary gain control for the mic input, providing gain between 10 and 60dB in decade increments. The microphone input uses the 'A' socket on the rear panel.

Next, another illuminated button (orange) selects the line input via another relay and another rotary switch provides gain from -10 to +15dB in 5dB steps. The line input is connected via socket 'B', so can be accessed easily from the multi-channel D-sub interface. The final control in this section is a continuous gain trim providing up to a further 10dB of gain, allowing the level of the selected input to be fine tuned, and affording a useful maximum 70dB of gain for the mic.

Running vertically up the side of these controls is a 12-segment LED bar-graph, which shows the preamp's output level relative to the digital output of the Black-series A-D converter (if installed). In other words, the meter is calibrated in dB Full Scale, where 0dBFS equates to +18dBu (the European standard alignment level). Usefully, there's also a separate 'Over' indicator that illuminates at +19dBu (1dB higher and 2dB below the preamp circuitry's actual clipping point at +21dBu).

The next section of the front panel provides a continuously variable high-pass filter (low cut), with a second-order slope (12dB/octave) and a turnover point that can be varied from 30 to 225Hz. Another illuminated push-button (orange) here switches the filter into circuit.

Next, we have the preamp's 'quirky' feature — the HMX control. Audient describe this as adding a solid-state 'triode' gain stage to enhance low-order harmonics. There is another illuminated push-button (red) to activate this feature and a rotary control scaled simply from 0 to 10. The higher the number, the more harmonic distortion is introduced and the richer (or more crunchy) the sound becomes.

Lastly, a quarter-inch socket at the bottom of the panel provides an instrument or DI input. Plugging into the DI socket overrides the physical mic and line inputs but, rather cleverly, the mic and line gain stages can still be selected to process the DI input by using the Line switch in the usual way. This means there's a lot of gain available if needed, and you can choose whether to work with 10dB or 5dB increments! The DI input presents an input impedance of over half a MΩ, so there is no problem in loading guitar preamps.

EQ Module

I found the EQ module the hardest to fathom just by looking at the control panel, mainly because the controls aren't laid out in the conventional order and have slightly unusual names. What we have here is a four-band equaliser, but it doesn't follow the usual 'two shelves and two parametric mids' topology. The 'A' input is not used for the EQ module at all, and only the 'B' input and 'C' output function.

Starting at the top again, we have a conventional HF shelving section with a grey push-button to switch the turnover frequency between 8kHz and 'air' (a much higher turnover frequency, which I'd guess is about 15kHz). A continuous rotary control provides ±15dB of gain swing, with a gentle detent at the unity gain position.

In addition to the expected controls, the EQ module includes two interesting tools for manipulating the LF band: the Overtone mode adds subtle harmonic enhancement; and the Glo function boosts and compresses it, thickening the bass end and making it more consistent.In addition to the expected controls, the EQ module includes two interesting tools for manipulating the LF band: the Overtone mode adds subtle harmonic enhancement; and the Glo function boosts and compresses it, thickening the bass end and making it more consistent.Photo: Mike CameronThe LF shelf section below is equipped with a rotary gain control covering the same range and another (grey) push-button to switch the turnover frequency between 50 and 100Hz. To the left of these controls are two illuminated push-buttons for the Overtone and Glo modes. Overtone adds some subtle harmonic enhancement to the LF band, with the amount being proportional to the extent of boost or cut being applied. In other words, the harder you push the bass, the more crunchy it becomes. The Glo function is entirely different and acts to boost and compress the LF band. It is reasonably subtle, but it makes the bass end thicker and more consistent, and is a remarkably useful effect.

The third EQ band is labelled Presence, and its ±15dB gain control is supplemented by two grey push-buttons. The first switches the centre frequency between 1.5 and 3kHz, while the second determines the shape of the bell filter between the normal symmetrical, broad boost and cut modes, or to provide a broad boost but narrower cut. The latter is useful for surgical tweaking, while the former is better for general tonal shaping applications.

The fourth band is the low-mid frequency section and this is more like a conventional parametric EQ. Two rotary controls determine the centre frequency (125Hz to 2kHz) and the gain swing (±15dB). Another grey button changes the filter shape in the same way as for the presence band — with symmetrical broad cut and boost curves, or broad boost and narrow cuts.

A blue, illuminated button at the bottom of the panel provides an overall 'EQ In' switch, to allow comparison between source and equalised signals, and a three-position toggle switch allows a degree of spectral tilting to be introduced. Strangely, the EQ button doesn't bypass the Tilt function — which makes sense when you think about it, but caught me out initially.

The Tilt function pivots around 1kHz and provides a gentle 2dB slope to either boost the highs and reduce the lows, or vice versa. The central position of the switch provides a flat response. I first came across this 'tilt EQ' idea in a Quad hi-fi preamp many years ago, and it is surprisingly effective in shaping overall tonality.

Compressor Module

The optical compressor module has most of the usual controls you'd expect to find, which makes it seem very familiar, yet there's also a scattering of buttons for unusual functions. On the rear panel, the 'A' connector provides an external side-chain input, while the 'B' input and 'C' output carry the audio signal.

The top of the panel is filled with a round VU meter, which can be switched by an illuminated button below to show either output level or gain reduction. When configured to show the output level, 0VU corresponds to +4dBu, and in gain reduction mode the needle rests at 0VU and moves to the left to show increasing gain reduction, in the usual way.

The first rotary control sets the level of the input signal, and this essentially determines the compression threshold. The threshold is actually fixed at -20dBu, so the amount of compression applied to the signal is determined by adjusting the input attenuation across a range from -30 to 0dBu. A second rotary control sets the output level, with gain ranging from 0 to +30dB to compensate for the level lost through compression (or input attenuation).

Another illuminated push-button selects the external rear panel ('A') input to feed the side-chain instead of the audio input signal. This allows various side-chaining effects to be created, such as frequency-conscious compression and auto-ducking.

The lower half of the panel contains the normal compression controls, namely Attack, Release and Ratio — all six-position rotary switches. Attack can be varied from 0.1 to 30ms, in well-judged steps, and Release from 0.1 to 1.4 seconds, with the final position bringing in an automatic release mode. The ratio is configurable from a very gentle 1.2:1 up to 8:1.

Running down the left-hand side of these rotary controls are more illuminated push-buttons. The first introduces the Overcomp mode, which essentially places a second, fixed compressor in series ahead of the main compressor. It is very much an effect, but can be used creatively on drums and guitars, and it can be controlled to a degree by varying the input level. The second button is labelled 'Smooth' and switches the side-chain to a clever combination of peak and gentle RMS sensing, which controls average levels, while still noticing and controlling peaks.

Finally, two more illuminated push-buttons are used to switch the entire compressor in or out of circuit, and to connect the side-chain to a link bus in the frame for stereo or surround linking of multiple compressors. Usefully, the first eight rack positions share one link bus (allowing anything up to 7.1 surround linking) and the last two share a separate bus. This split link bus allows for two independent stereo compressor setups using different types of modules, if required. When compressors are being linked, all the controls have to be set identically on all linked modules.

ADC & Master Clock Modules

The last two modules in the review rack were the Analogue to Digital Converter (ADC) card and the Time Machine master-clock unit. Compared with the rest, these units are positively boring in their features and facilities, but they serve critical functions and have been designed with the same attention to detail.

The ADC module provides extremely high-quality stereo A-D conversion and is built around the class-leading AKM 24-bit, 192kHz chip. The output is provided simultaneously as AES3, S/PDIF and TOSlink outputs on the front panel, plus another AES3 from output 'C' on the back panel. All interfaces can support output sample rates up to 192kHz with 24-bit word lengths. The converter can run from its internal clock, or use an external clock. If the Time Machine module is fitted, the external clock option is automatically fed from this master clock unit. If absent, the rear-panel BNC socket is used to input an external clock instead.

The top half of the ADC panel is dominated by a 12-segment stereo bar-graph meter, scaled from -36 to 0dBFS. From the factory, 0dBFS is configured to equate to +18dBu, but internal jumpers allow alternative calibrations of +20, +22 or +24dBu. Like the preamp module, additional 'Over' LEDs are configured to illuminate 1dB higher than the 0dBFS calibration.

A grey push-button cycles around the internal sample-rate options (from 44.1 to 192 kHz), before checking the external input. The internal modes are indicated by yellow LEDs, while the external clock source is indicated by a green LED (which flashes if a suitable clock is absent).

The ADC's analogue inputs are connected via the 'A' and 'B' sockets on the rear panel, while the 'C' socket provides a duplicate AES3 output (although this is not electrically separate from the front output).

The 'Time Machine' module is designed to serve as a studio master-clock source, providing sample rates up to 192kHz. When used to control Black Series ADCs, its word clock is distributed within the rack on a specially optimised bus, to ensure that jitter remains as low as possible. The clock output is made available on the rear-panel BNC connector, and as an AES3 signal on a front-panel XLR and the 'C' output XLR.

A grey push-button allows the sample rate to be selected in the same way as on the ADC module, while a second button slaves the master clock unit to an external input via the BNC socket.

In Use

The Black Series certainly looks and feels the part, with a professional appearance, and sturdy switches and buttons. The cable from the power supply looks strong enough to tow jumbo jets, and everything connects on balanced XLRs (or balanced D-subs), so there shouldn't be any interfacing problems.

With the HMX circuit switched out, the preamp is very clean-sounding — very similar to the lovely ASP008 preamps, in fact — with a very open, transparent high end, a big, solid bottom end, and a very low noise floor. The HMX control introduces some interesting harmonic richness, and I like the fact that it can be used on both mic and line sources. I used it to process some stereo mixes and liked what I heard — it's not unlike the valve harmonics function on my beloved Drawmer mastering processor.

Each of the 10 module slots has three XLR connectors, providing two inputs and one output, although the actual implementation varies with the different modules.Each of the 10 module slots has three XLR connectors, providing two inputs and one output, although the actual implementation varies with the different modules.Photo: Mike CameronOn the microphone side, the HMX facility works in a similar (but slightly stronger and more pronounced way) to the VHD mode on some of the newer SSL preamps. As you would expect, though, it doesn't enhance all sources equally — it works really well on some sources, but seems to muddy things up on others — and I guess the effect could become recognisable if over used. So it's a case of applying sparingly across many sources, or more heavily for effect on just one or two.

The EQ was even more interesting to use. At first I didn't think I'd be able to achieve what I wanted with the controls provided — particularly because of the apparently limited facilities of the presence band — but in fact I soon found that I could do everything I needed to polish individual sources or complete tracks with surprising ease. For the latter, having to operate two units side by side for stereo sources was something of a pain, but the results justified the (small) frustration.

My overriding impression of the EQ is that it is supremely musical: everything just works perfectly, regardless of the kind of music or source instruments. The quality is easily up there with the greats too, but it isn't a copycat — it does its own thing and has its own subtle, but very desirable, character. Clearly, this is designed with musicality and creative tonal shaping in mind, rather than as a traditional engineer's surgical tool, so it requires a different approach in use, but there's no doubting it works, and once familiar it's very easy to drive.

Using just the shelf sections, I found I could get an almost 'vintage' flavour — not unlike a good passive EQ — and I found the 'air' mode was wonderful for adding exactly that: a sense of air and openness without going over the top. However, I also found that the effect could become slightly aggressive if combined with the high Tilt control, so best to use one or the other, but not both!

Setting the Tilt filter to boost the bass is very useful. It just softens the sound gently, taking the edge off overly bright sources but without obscuring the clarity or changing the overall character too much. It just makes the sound slightly warmer and gentler.

The ability to narrow the cutting bandwidth of the low-mid and presence bands is very useful, and effectively negates completely the need for a Q or bandwidth control. In fact, the Presence control was perfect for lifting vocals in a mix or for taming overly 'middy' electric guitars. Although there are only two centre-frequency options, one or the other always seemed to work perfectly, regardless of the source!

The Overtone function is another flexible and musical option, but again, not one to over-use. It can add body to weaker instruments, but can also create muddiness if overdone. The Glo function is a new effect for me, but one that is remarkably useful for adding some weight and substance to weak-sounding sources — especially keyboard bass lines and bass guitars. It did nice things to a boringly clean Hammond Organ patch too. The clever thing, though, is that while the Glo process bolsters the bass end of instruments (or a mix), it doesn't seem to become overpowering.

The compressor is very civilised most of the time and just gets on with the job in a typically smooth, opto-compressor kind of way. However, the Overcomp mode can introduce some pretty aggressive energy on drum and guitar or bass tracks. I found the Smooth setting worked very well on transient acoustic guitars, in particular, where it was able to provide the required degree of compression without being fazed by transient dynamics. It did what the button said, giving a smooth, controlled effect.

The A-D converter performed extremely well, and I preferred it in a straight A/B comparison with my now ageing Apogee PSX100. The top end was slightly smoother and more refined, and the stereo imaging seemed even more crystal-clear and solid — which is a sure sign of very low jitter.

Overall, the Black Series is a very impressive kit of parts, and its flexibility and configurability allows it to meet the needs of pretty much any application: it can be a rack of preamps, a stereo recording front end or post-production tool, or a set of very high-quality converters — or combinations of all of these. There's also a more portable, four-module version on the horizon, which might broaden the appeal.

Some may be disappointed that there are no facilities for function recall, as there is on the SSL X-Rack or the AMS Neve outboard, for example, but I don't see that as a major disadvantage at all. Clearly, there's also a lot of scope for additional modules to extend the rack's functionality and versatility in the months to come, and I can't wait to see what turns up. Definitely a system to be auditioned if your budget can take the strain. Highly recommended. 


The obvious rivals for the Black series are the ever-expanding API Lunchbox system, which has the advantage of a lot of third-party modules to choose from, and the SSL X-Rack system, which has a built-in and very elegant Total Recall system. There's also a similar modular system offered by Tonelux, and the Rupert Neve Designs' Portico system is worthy of consideration too. Despite the fact that the last is not configured as a conventional rack system, it can be used in a similar way.


  • Audient's usual high-quality construction.
  • Superb audio fidelity, with very impressive sound-shaping facilities.
  • Flexibility of configuration.
  • Well thought-out interfacing options.


  • A full rack of modules is expensive, but not unreasonably so.
  • XLR patch cords not supplied.
  • I'm struggling to think of anything else.


This flexible, modular series of signal processors is built with Audient's usual high quality and attention to detail, and comes with an interesting range of unusual features for creative tone shaping and control. Suitable for a wide range of applications and well worth a closer look.


BR10 Rack (the chassis) £582; modules £254 each; blank panels £23.50 each. Prices include VAT.

SCV London +44 (0)20 8418 0778.

+44 (0)20 8418 0624.