Audient Centro Master Section

As more people leave behind their mixing desks, many find they still need a good monitor controller.

Working practices continually evolve, and while the mixing console was once the technical and ergonomic hub of the studio, that role is now taken by the DAW for most people. Console input channels have been replaced with computer interfaces combined, perhaps, with a few esoteric rack units, while the console monitoring functions are handled by some sort of monitor controller — and there are a lot of options to choose from, spanning all budget levels and with a wide variety of features and facilities.

The UK manufacturer Audient is probably best known for its superb ASP8024 console, but the very highly regarded ASP510 surround-sound monitor controller has also been a big hit in the appropriate circles. It always seemed odd to me that an equivalent stereo controller wasn't available, but Audient have at last addressed that with the Centro Master Section.

Overview

The term 'Master Section' is appropriate — this is a lot more than just a stereo monitor controller, and it embodies the very high sound quality and practically bomb-proof and thoughtful design that we have come to expect from Audient.

The Centro is a two-box design, with a 2U rackmounting unit controlled from a separate desktop panel. Everything feels solid and reliable and it looks very professional. The input selector accommodates up to six digital inputs and six analogue inputs, and these can be routed in various ways to two independent headphone cue mix outputs and the control room monitors. There is provision to switch up to three pairs of control room monitors, plus a dedicated subwoofer feed, and there is also a talkback facility. All signal paths are active — unlike much of the competition, that uses passive attenuation — but Audient's attention to detail, and the use of digitally controlled attenuators (DCAs), has ensured that sonic quality is superb. Unlike some of the competition, the Centro cannot be expanded to provide surround sound monitoring. What you see is what you get: a comprehensive and well thought out stereo master section.

Connections

The rackmounting unit is the hub of the system, and almost all the audio connections are made on its rear panel. It measures 220mm front to back and weighs about 5kg. There are two rows of connectors, with the top row being mainly concerned with inputs, and the lower row with outputs. Starting at the right-hand side and moving left, the first connectors are two pairs of phono (RCA) sockets to accept unbalanced -10dBV inputs from semi-professional or domestic equipment, and these are labelled as Stereo Inputs 2 and 3. Stereo Input 1 is provided with a pair of XLRs for balanced +4dBu signals.

The other three analogue inputs, labelled Mix input, Foldback input and Record input, are all on XLRs and expect +4dBu balanced signals. The names clearly suggest the intended applications, but I'll come back to these in more detail later.

The digital inputs are accommodated by three more XLRs for AES3 signals, plus a pair of phono (RCA) sockets and a TOSlink connector for S/PDIF signals. There is also an AES3 output which echoes any selected digital input to feed a digital recorder or an external D-A converter. All the digital inputs can accommodate sample rates up to 192kHz and 24-bit word lengths.

Two final connectors in this top row are a quarter-inch socket for a (foot) switch to activate the talkback microphone, and a nine-pin D-sub socket that links to the remote control panel.

The bottom row of connectors are all XLRs, apart from the fused IEC mains inlet and a voltage-selector switch. Starting from the left this time, the first three pairs provide control room monitor speaker feeds, followed by an analogue Recorder output, Foldback Mix 'Thru', and the two stereo Cue headphone outputs. The 'Foldback Mix Thru' connectors provide a direct copy of the Foldback Mix inputs, the idea being that the main DAW output could be connected to the Foldback input, and then looped back across to the Mix input, so that the same signal can be easily allocated to the control room monitoring and Cue feeds. The last XLR is for an external talkback microphone input.

The rear panel of the rackmounting part of the Centro provides the main connection hub, with a good range of analogue and digital connectivity.

Front Panel

The front panel features a range of controls to adjust the critical input and output levels, as well as to configure some operating modes. In the bottom left-hand corner of the panel is a screwdriver preset control for adjusting the input level of an external talkback microphone. If required, an internal jumper link can be used to provide low-voltage phantom power to the rear-panel talkback mic input. Although this is only 18V (rather than the normal 48V), it is sufficient for a wide range of capacitor and electret mics.

There are seven other rotary controls across the front panel, which allow the levels of the six analogue inputs and the output of the internal D-A converter to be balanced against one another. By default, all inputs operate at preset sensitivities, but pressing the illuminated blue 'Uncal' push-button adjacent to each level control brings it into the signal path to provide ±12dB of gain trim.

Two yellow push-buttons on the rack panel configure fundamental operating modes. The first determines the signal that feeds the analogue Record output (either the dedicated Record input or the output of the monitoring source selector). The second button decides how mono signals are auditioned, with the choice being as a phantom image across both monitors, or purely from the left monitor. The former is useful for checking the imaging accuracy of the monitoring system, while the latter is better for assessing the true mono balance as heard on a single-speaker system.

Remote Control

The desktop controller measures 240mm wide by 155mm high, and is about 45mm deep. It weighs 0.9kg, which is enough to feel solid without being excessively heavy. The rear panel carries a nine-pin D-sub socket for the connection back to the rack unit, plus a stereo quarter-inch socket for the engineer's headphones. A pair of small push-buttons reconfigures the Alt 2 monitor output to feed either a mono or stereo subwoofer system.

The control surface is divided into four logical subsections by a neat surface-etching process. To the left is the input source selection, with cue output controls near the centre, the control room monitoring to the right, and talkback at the far right.

Source selection is fairly intuitive but, as mentioned earlier, three of the analogue inputs are predefined for specific functions. The Mix input is intended for the main stereo output from the DAW, while the Record input is meant for the source being recorded. Typically, this might be the output of a vocal mic preamp, for example, and routing this signal via the Centro ensures latency-free monitoring for the performer. By default, this Record input is also routed directly through to the Record output sockets, which can be connected to the DAW's record input (although a button on the rack unit allows the Record output to follow the monitoring source selector instead, as mentioned earlier).

The Foldback input is intended for a click track or backing track, typically provided by a separate output from the DAW. Both the Foldback and Record inputs can be switched to mono, so if only one channel is being used the signal will appear as a phantom centre image on the outputs. Also, both the Record and Foldback signals can be routed to the cue headphone mixes, as you would expect.

The Centro contains a single stereo D-A converter, but its source is selected from any of the six digital inputs. The output of the D-A converter is presented as another analogue source, and its level can be adjusted, if necessary, from the main rack panel, to help balance levels when making A/B comparisons.

Usefully, analogue inputs can be selected individually, or combined to form mix groups. For example, a live input could be auditioned with a CD replay, to rehearse or work out a new part. To mix signals, you simply hold down the button for one source and then add the others by pressing them. Double-tapping any source button cancels the mixed group and reverts to single-source selection again — but the previous mix group is remembered and can be recalled if required.

The digital output socket on the rack panel can be configured to pass on a selected digital input independently of the source selected for the D-A converter. This is achieved by holding down the Digital Out button on the remote panel and selecting the required source. However, there is no provision here for sample-rate or word-length conversion — so don't try to record the 24/96 output from your DAW directly to a 16/44.1 DAT machine!

Cue Mixes

The Cue mix section is a little convoluted, but works well in practice. Basically, there are two independent Cue outputs, each provided with an either/or source selector. Cue 1 can monitor either the selected control room source or the dedicated Record input feed. Cue 2 can monitor either the selected control room source or the dedicated Foldback Mix input. Each Cue output has its own volume control and can be auditioned in the control room by pressing the appropriate Listen buttons to check that the performer is getting the correct feed.

So far so good, but what if you want to provide a cue mix that combines the live Record input feed with the DAW backing track replay, for latency-free monitoring? The answer lies in another push-button that mixes the Cue 1 output into Cue 2, while simultaneously switching both Cue output sockets to provide the new Cue 2 signal. The Record source is selected for Cue 1 and the level adjusted appropriately using the Cue 1 volume control, while the DAW backing track is selected for Cue 2 either as the dedicated Foldback input or as the DAW Mix control room source. The overall Cue monitoring volume is set using the Cue 2 volume control, and the mix is made available on both Cue output sockets.

Control Room Monitoring

The control room monitoring section features a comprehensive set of facilities, with a large rotary control for the overall volume, separate ±8dB gain trims for the two alternate speaker outputs, and a dedicated volume control for the engineer's headphones. The three monitor selector buttons are interlocked so that only one set can operate at a time, and a separate button activates the engineer's headphone output.

To accommodate different amplifier sensitivities, each of the three stereo monitor outputs can be adjusted independently with up to 15dB of attenuation. This is achieved by holding the selector button for the required monitor output, and then pressing one of the six digital input source buttons. Dig 1 provides zero attenuation, while Dig 2 is -3dB, Dig 3 is -6dB, and so on up to 15dB of attenuation with Dig 6 selected.

Below the main volume control are two buttons to provide a complete output mute or to Dim the monitors by a preset amount. The latter is adjusted by holding the Dim button down until it flashes and then adjusting the main volume control to the required level. Pressing the Dim button again restores normal operation and saves the required Dim level.

There are also separate mute buttons for the left and right channels, which are very handy for assessing the listening environment and the correct functioning of each monitor. Unusually, this facility can be used in conjunction with a mono sum selection to allow the mono signal to be monitored as a phantom centre on both speakers, or just on one speaker. For example, select 'mono' and 'mute right' to listen to mono on the left speaker only! However, in this case the channel mute buttons operate via the DCA to give click-free soft muting, and the DCAs are before the mono and phase-reverse circuits. Consequently, a separate system was required to provide the mono audition modes.

So, given this facility, the obvious question to ask is why a separate button was provided for phantom/left mono auditioning on the main rack unit? The surprising answer is that these separate channel mutes operate on the inputs to the monitor control section rather than the outputs, and thus operate before the mono sum circuitry, instead of after it. I can't see any logic for this at all, I'm afraid, and it makes operation of the system less flexible than it should be.

The mono button itself is positioned above the main volume control, along with a left-channel polarity reversal button. Many quite expensive monitor controls lack the polarity reversal facility, but is an essential one in my book. Being able to flip the phase of one channel is helpful for checking phase and imaging anomalies, and being able to do so ahead of the mono sum circuit means that the difference (S) signal can be auditioned as well as the mono sum (M). Auditioning the S signal is extremely handy for quick alignments of stereo channels and stereo microphones, as well as for assessing the mono compatibility of reverbs and effects. A nice feature here is that the Phase button flashes when latched on, to make sure you don't forget about it!

If the Alt 2 output is reconfigured for use as a subwoofer feed, the trim control is sensibly disabled and a pair of yellow LEDs indicate the current subwoofer mode as set on the rear-panel buttons. The operation of the subwoofer system underwent a radical change recently following a discussion I had with the designer, Dave Dearden. Previously, a single, pre-selected subwoofer mode remained active regardless of which monitor output was selected, and this seemed rather unhelpful. The new update allows completely independent subwoofer modes to be configured and stored for the Main and Alt 1 monitor selections. So you can now set the system up for, say, a stereo sub on the main outputs and no sub on the Alt 1 output — or any other combination you like. The LEDs on the remote front panel indicate the current mode for each monitor output.

The final section of the controller provides Talkback, and is very straightforward. A rotary control sets the sensitivity of the microphone (up to 60dB of gain is available), which is mounted flush with the panel surface. Talkback to the Cue outputs is activated with a push-button that provides a momentary mode if held and a latching mode if pressed and released. When latched, the button illumination flashes to remind everyone about the open mic! The control room monitors are dimmed automatically whenever talkback is activated, to prevent howlrounds.

Conclusion

The Centro boasts an impressive technical specification and its analogue inputs sound very clean and open. Stereo images are portrayed with wide and stable sound stages, and the D-A converter section also turns in a very credible performance for the price. Source selection is simple but flexible, and the ability to fine-tune input levels makes A/B comparisons very straightforward. Having to make these adjustments on the rack unit isn't quite as convenient as controlling them from the remote controller, and means that the rack unit has to be mounted within reach, but I doubt this will be an issue for most users.

The Cue system is flexible and the control room monitor section does all that could reasonably be expected of it. All in all, this is a very nice monitor controller that ticks all the boxes for build and sound quality, as well as flexibility and usability, making it definitely one to add to the shortlist!