The birth of Digital Audio Workstations (DAWs) has brought about a major change in the way we record, mix and, in short, work in recording studios. One of the side effects of the arrival of these digital workstations is that, in some facilities, a piece of gear that until recently was the central pillar has been done away with: the mixing console. Whether because of the flexibility of mixing in the DAW, the possibility of feeding the A/D converters through outboard preamps and equipment, or simply because the budget wasn't enough to buy one and DAWs make it possible to work without it, the fact is that some studios no longer have a console, or it has been relegated to the background.

This is especially true in small studios where, nonetheless, it is common to find several pairs of monitors, largely due to the proliferation of active monitors and the resulting drop in prices.

Apart from the obvious implications of not having a mixing console in the studio, one that may go unnoticed at first is that you no longer have the monitor section (or whatever it was called) that let you control several pairs of monitors. Without this section, the task of checking how the mix translates on different systems, or comparing the mix with a reference, can become tedious.

This is where monitor controllers make up for that shortcoming. Essentially, they are units that replace the console's monitoring section, letting you connect different sound sources and route them to multiple pairs of monitors. It is also common for them to include a talkback mic, another feature that usually goes with the console, but one that is more easily made up for if you have a spare input channel.

The unit at hand is a monitor controller from the manufacturer SPL. The people at Sound Performance Lab have vast experience in the pro audio world, with a wide variety of products: mastering consoles, equalizers, dynamics processors, mic preamps, analog summing mixers...

When designing the MTC 2381 (the initials stand for Monitor & Talkback Controller), they decided to go for a simple, functional unit that would offer the cleanest possible signal path.

The result is a controller that can feed three pairs of monitors and a pair of headphones, and has four stereo inputs, talkback and a headphone amp with a cue mix for the musician.

The controls
The monitors are connected through three pairs of XLR connectors. The input for the main mix (Mix) has two TRS connectors (unless otherwise stated, all connections are balanced).

Two more pairs of TRS connectors are available for the first two 2-track sources. These stereo inputs (2TRA and 2TRB) are designed for connecting professional CD/DAT players or, for example, for receiving the signal from an alternative D/A converter.

The other two stereo sources (2TRC and 2TRD) connect to the MTC via unbalanced RCA jacks, intended for signals from consumer players. That's why these inputs have a fixed +10 dB boost, to raise the signal from this equipment to the level of the other inputs, thus avoiding level changes every time inputs C and D are used.

Cue Mix
A special feature of this controller is that it lets you create a zero-latency headphone mix for the musician. Aware of the market the unit is aimed at—DAW users—SPL has included a set of controls for setting up a cue mix in case latency is a problem in the system.

For this there is a stereo input called Musician (two TRS jacks), into which you feed a copy of the musician's signal before it enters the DAW, for example through a secondary output on the preamp being used, or via the interface's direct outputs.

This signal is combined with the controller's main bus (the one heard on the monitors) and sent through another two TRS connectors (Cue Mix output) to a headphone amp for the musician.

Talkback
The talkback mic is an omnidirectional electret activated by a push button, although on the back there is an input for a footswitch in case you want to activate the mic with a pedal.

The signal from the mic is routed internally to the musician's headphone mix, but it is also available at an alternative output called Talk Out.

This is useful for sending talkback to a second room, or if you want to communicate through an additional monitor instead of headphones. Of course, this output also makes it easy to try experiments along the lines of "let's record the bridge vocal through the talkback mic."

The last connection available is called Slave Out, and it offers a sum of all the inputs (Mix and 2TR) to be sent to external metering equipment (VU meters, for example), a recorder, etc.

The front panel
Once you know all the MTC's possible connections, the layout of the front panel makes perfect sense.

The top section houses a series of independent push buttons that let you select which sources (Musician, Mix and 2TR A, B, C and D) will be available on the different monitors (SP1, SP2 and SP3), on the control room headphones and at the Slave output. This way, any combination of input sources can be sent to the main bus, and this can be monitored on one or more pairs of monitors and/or on the headphones.

Next to the SP buttons there are three more: Mono, Dim and HP On. The first is for checking mono compatibility, Dim attenuates all active outputs by 20 dB, and HP On turns the control room headphones on or off.

All these buttons have their own LEDs, which light up to show they are active: orange for the sources, yellow for the monitors, red for the Mono, Dim, HP On and Talk controls, and blue for power.

The Cue Mix section lets you adjust the musician's headphone mix, with knobs that set the level of the Musician and Mix signals and of the section's own headphone output.

In the Talkback section you'll find the button for activating the mic and a knob for setting how much signal is sent to the Cue Mix and Talk Out outputs. When Talkback is activated, the 20 dB attenuation kicks in automatically to prevent feedback. Finally, the Control Room section has two more knobs. The first lets you adjust the balance between the Mix signal and the rest of the signals on the main bus.

The second knob in this section is the one that sets the main bus output, and it is somewhat larger than the others. Its scale is marked in percent, and the signal physically passes through it, to avoid the distortion or coloration associated with control elements such as VCAs.

Calibration
As mentioned at the beginning, SPL decided to take a purist approach when designing the 2381 and has tried to avoid active components wherever possible.

That is why the inputs and outputs have no trims for matching the levels of their respective signals.

Since, to use a controller optimally, the input signals must be matched and so must the levels of the different monitors, the lack of these trims on the controller itself may seem like a disadvantage at first.

However, as SPL points out, the truth is that the input sources and monitors will probably have their own level controls, so including them on the MTC as well would be redundant and would be detrimental to the signal.

Personally, I agree with this position, because although calibration may be somewhat more tedious since it has to be done on several devices instead of just one, the truth is that it is not something you do every day, and the cleaner the signal path, the better.

In action
After calibrating the system, the first tests were done during a vocal recording session, making use of both the monitoring features and the talkback and cue mix sections.

For the latter, the musician's headphone mix was set up slightly differently from the way SPL proposes, since SPL's approach uses the same "base" mix for the control room and the live room, differing only in the proportion of the performer's signal.

This isn't always desirable, since the instruments the musician needs to hear are often quite different from the ones the recording engineer needs to hear.

So, taking advantage of the fact that latency was not a problem in the system, we fed a reference mix tailored to the musician's taste directly into the Musician input, including the performer's own signal coming from the DAW.

By keeping the Mix knob in the Cue Mix section all the way down, it was possible to send the musician a mix completely different from the one heard in the control room.

The rest of the tests were done while mixing the same project, and several intensive listening sessions were also carried out. All of this confirmed the quality of the 2381 controller.

Conclusions
The most notable thing about the sound of this unit is that there is nothing notable about it. In other words, a monitor controller should only serve as a switcher/router; it should never leave its mark on the signals that pass through it.

Here, SPL's purist philosophy pays off, and the MTC 2381 delivers a clean, clear sound with no coloration whatsoever: signals reach their destination with no evidence of having passed through the unit.

As for the controls, they are all useful and robust, and they make operation simple and intuitive. Where needed, the knobs have multiple positions, all labeled, to make it easier to recall a particular setup.

It is also true that the MTC offers fewer features than other controllers in its price range, but if that has meant better quality in the rest of the components, there is nothing to complain about.

It feels as though SPL analyzed the real needs of a monitor controller and implemented them in the 2381, getting rid of unnecessary extras that would have made the unit more expensive.

The result: a highly functional controller whose main feature is the solidity of its sound.