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Edirol M16DX

USB Digital Mixer
Published July 2007
By Tom Flint

Edirol M16DX

This new USB-equipped mixer has a control surface and a separate I/O unit, but are two boxes better than one?

The M16DX is a 24-bit, 96kHz, 16-channel digital mixer. It incorporates some of Roland's respected COSM effects, a room acoustic analysis tool, and comprehensive USB connectivity for multitrack computer recording. The hardware is unusual in that it is divided into two separate modules that are linked to one another via a two-metre cable (an optional seven-metre one is also available). At one end is a compact mixing board with EQ, pan and other fairly standard channel controls. At the other is a box housing nearly all the inputs and outputs (I/O). Unlike many small mixers, which add USB to the stereo output as a means of capturing the final mix, the M16DX has a post-EQ, pre-fader send from all 16 channels, as well as a stereo master mix send that can be 'finalised' using internal mastering processors.

As part of the package, Edirol provide a copy of Cakewalk's Sonar LE, which makes this a reasonably complete basic production setup for anyone with a computer. Both PC and Mac drivers are now available, though the Mac drivers hadn't made it onto the install CD provided (they can be downloaded from the Edirol web site).

Overview

The control half of the M16DX is surprisingly small, with almost exactly the same footprint as a copy of Sound On Sound. It is clearly designed to sit unobtrusively on a desktop, and this is no doubt why Edirol banished the I/O (and therefore the majority of the wires) to another box. That said, the back panel does house some connections and features, the most important being the 'DX Bus' 15-pin D-Sub connector, which links the two boxes and carries power (this means that only the I/O module requires a mains input). Also on the back is the single headphone feed, located next to a pair of quarter-inch jack sockets that act as Control Room left/right outputs and carry the same signal as the headphones. The module also has some inputs, the first of which are two jack sockets that are wired to channels 15/16 and labelled Aux Returns 2. Further along is a stereo mini-jack input, which is actually routed to the same two channels but overrides them when it receives a connector. This is intended for use with MP3 players and other such devices.

The rear of the controller module also includes the microphone used by the on-board room acoustic analysis tool to measure the response of a test signal played in the surrounding environment. Based on the measurement, the tool applies a 16-band EQ profile to the stereo output as compensation for any imperfections. Of course, it won't always be possible to place the M16DX's sensor in the optimum listening position, so it is also possible to use a mic connected to input channel 1 (See the box elsewhere in this article for more about this).

The compact surface includes all the usual controls you'd expect to find on a small mixer. The single aux control on each channel is switchable between the two aux channels.The compact surface includes all the usual controls you'd expect to find on a small mixer. The single aux control on each channel is switchable between the two aux channels.The rest of the various input and output sockets are distributed across the front and back faces of the I/O module. The front (identified only by the rack-ear attachment screws on either side) is largely taken up by the inputs that feed the first four mono mixer channels. For each one you have the option of using a quarter-inch jack connector at line level, or hooking up a microphone to the XLR socket. Switchable phantom-power is available via the XLR sockets.

All four channels have their own high-pass-filter switch and preamp gain control, which are found on the control module. Inputs 1 and 2 differ from 3 and 4 in that they have an extra 'HZ' button that makes them suitable for high-impedance instruments such as electric guitar and bass. The only other I/O on the front, aside from the main power switch and DX Bus socket, is the digital ins and outs: S/PDIF and ADAT.

The module's rear is mainly populated by quarter-inch jack sockets, 10 of which feed stereo channels 5 to 14. Above these are the Main outs, Aux sends 1 and 2 and the Alt (alternative) outs, the last of which can be monitored via headphones or routed to the main mix bus. The first 12 mixer channels can be muted from the main mix and sent to the Alt bus, thereby making it possible to set up a separate submix for isolating click tracks, establishing foldback mixes and so on.

Also on the rear panel is a pair of line-level RCA phono connectors for use with cassette recorders and similar devices. One last pair of RCA sockets is routed to channels 15/16. These inputs will be mixed with any other audio signals that are routed to these channels, regardless of whether they are from the control module's quarter-inch sockets or the mini-jack one. The rest of the panel real-estate is taken up by the inputs for the external power supply and the USB lead.

The Controls

On the mixer module, mono channels 1-4 and stereo 5-12 all offer the same EQ, pan, aux send, channel select, solo, mute and level controls. The stereo pair 13/14, intended to be used for the USB and/or the Aux 1 return signal, and channels 15 and 16 differ in that they have only a level control.

The EQ enjoyed by the first dozen channels is a straightforward ±15dB three-band design, with shelving filters set at 400Hz and 2KHz. A more flexible mid-band can be swept from 200Hz to 7.4kHz and its Q curve can be altered from a steep and surgical 8.0 to a broad 5.0 setting. Rather than adding two extra controls to each channel for adjusting the mid-band, two assignable knobs do the job for all 12, automatically acting on whichever channel is selected at the time they are moved.

Edirol have saved some more space by having just one row of channel Aux send knobs, even though there are two send buses. In this case, the row is assigned to either Aux 1 or 2/FX simply by pressing the relevant button, which lights up to indicate that it is active. Aux 2/FX, as the name suggests, doubles up as an effects send, feeding the internal processor when the appropriate button is pressed. There are also Master send controls for both Aux channels and a pre-fade button for Aux 1.

Sound Adjustments

At the rear of the mixer module is a panel of small, recessed switches that make it possible to alter the sensitivity range of all four preamps, from 50 to just 20dB (for fine adjustment), and to change the XLR and jack ins of channel 1 so they act as a sensor for the Room Acoustic Auto Control monitoring.

The acoustic analysis tool sends a series of noise bursts to either the Main or Phones/Control Room outputs. The active pair should be hooked up to the studio's monitors (or a venue's house PA) and the mic placed an equal distance in front of both speakers, with no obstructions. The speaker output is captured by the sensor mic but if the test signal level is too high or low, a warning is shown on screen. When the optimum level is found, a set of measurements is automatically taken for each speaker, and the M16DX makes suitable adjustments to the 16 bands of graphic EQ. The EQ compensation itself is calculated according to a user-specified preset. As a starting point there are three options, labelled Flat, Bumpy and Warm. Flat is self explanatory, whereas Bumpy boosts both the high and low end and Warm boosts the lower-mid range and attenuates the upper bands. There are, however, four user slots within each category so, for example, a favourite smile curve can be referenced as a template and applied to the room. It is also possible to narrow the range over which the frequencies are analysed and, for the non-flat settings, the overall amplitude can be increased or decreased. In addition to the auto feature, the 16-band graphic EQ can be set independently.

Effects

To provide the on-board effects and processing, Edirol have borrowed Roland's proprietary Composite Object Sound Modelling (COSM) technology. The five send effects available are a standard selection of reverbs and delays, which can be routed independently to either the Phones/Control room outs or the Main bus by pressing the relevant mix bus buttons.

Dynamics processing is also available, and can be applied to the first two channels by depressing the relevant Insert FX button. Here, again, there are five on-board Insert effects (however, only one processor can be used at a time). The options include three algorithms for amp simulation and compression, another offering a de-esser and enhancer, and another dedicated enhancer with some EQ control. There are no vocal compressors as such, but the three mentioned above can be used for this when the amp simulator module is turned down. The remaining processors are grouped in the Finalise section and include a multi-band compressor. Curiously, this section can't be used in the 96kHz mode, or in the USB stereo send path, though it is available for processing the signal when sent to the Main and Control Room outs.

The M16DX doesn't have much in the way of on-board memory, and there is no automation facility. Mixer setups can still be saved as 'scenes' but there are only eight slots, and it is not possible to recall them during a performance, as there is no MIDI control or tempo map.

Testing It Out

Mastering the M16DX's controls couldn't be much simpler, although the manual is required to establish exactly how the various monitoring options are configured. In most situations, moving a knob or pressing a button immediately changes the display to show the relevant controller information. A pair of backward/forward cursor buttons enables the user to select different screens, and a matching pair of Value buttons changes settings or scrolls through menu items.

The ins and outs are mainly located on the rackmount breakout box, though there are also some on the rear of the control surface.The ins and outs are mainly located on the rackmount breakout box, though there are also some on the rear of the control surface.The small screen has a very low resolution and renders its text and numbers rather crudely. Surprisingly, numbers and words are still reasonably legible. However, the display is recessed by several millimetres and is therefore partly obscured by the chassis when viewed slightly off-axis. In practice, therefore, the only way to see everything is to adopt a viewing position directly above the screen! As is often the case, the on-screen metering is not very helpful for establishing precise input levels and the main stereo LED meter is much better (although — a little disconcertingly for a digital mixer — this goes up to +20dB!).

Edirol have gone out of their way to fit all the necessary physical controls into a small space, but the rows are situated a little too close together. I found that the only way to tweak an EQ or pan control without moving the one above or below was by doing so with my fingertips. Slightly worryingly, the pots are capable of flexing somewhat, which is not ideal for something with potential live applications, where a few knocks are par for the course.

Edirol's space-saving idea of sharing one Aux level knob between two channels is less of a usability issue than one might imagine, as it only takes a quick button-press to reassign the knob. However one potential problem occurs when Aux 1 and 2 have completely different settings. For example, if Aux 1 is set to minimum and 2 to maximum, and the engineer switches from one to the other to make an adjustment, the encoder will hop to match its physical position as soon as it is touched, causing a dramatic level change which could be problematic in a live performance. Continuous encoders might have offered a better solution.

All the effects are of respectable quality, and their inclusion is welcome, though they are also extremely limited. The most obvious shortcoming is that, although the Insert effects can be inserted into both channels 1 and 2 for use on stereo signals, it is not possible to use different processor settings for each one, thereby preventing someone using, say, a guitar amp setting on one channel and a vocal setting on the other. Unfortunately, the processors also lack editing options. The tube simulator part of the Power Comp effect, for example, has just one control, as does the compressor. The effects block could also do with a cabinet simulator to be really effective for guitar processing.

USB

Installing the drivers proved to be very straightforward on my Windows XP system, and thereafter they appeared in the audio settings driver lists of all my audio and MIDI applications. To check the USB facilities I set up a muti-channel test recording using Cakewalk's Sonar 6, and recording turned out to be extremely straightforward. There is no need to enter a USB mode, as is often the case, so you quite literally just route the relevant ins to software mixer channels and hit record. Monitoring the sequencer output via the M16DX's channels 13/14 is less convenient, as there is no dedicated bus available. The only way to hear just output 13/14 is by muting all the other channel outputs or reducing their level.

A more problematic routing issue is that anything assigned to the Alt bus is not then fed to the send effects, even though the most practical way to separate the Phones/Control Room output from the main output is to route it to the Alt bus. The effects can be switched on and off for both the Headphone and Main Mix output, which is handy, but it would be much better if they could also be switched into the path of the Alt bus.

Design shortcomings aside, though, the sound quality is pretty high and noise levels are low. The preamps do get a little hissy at the top of their range but that is only to be expected. The EQ works effectively and squeezes the most from a limited set of controls, and I detected no zipper noise, be it on the EQ, pan or fader knobs.

Wish List

One feature that would be welcome is an EQ bypass, as it would enable the engineer to quickly check what effect their changes have made, and it would allow a flat signal to be sent directly to the USB port. In fact, better still would be the ability to send to USB pre-EQ: something for version 2, perhaps?

Given that the M16DX is a computer interface as well as a mixer, I was half-expecting to find that its knobs and buttons could send control data, allowing it to function as a control surface too, but there are no mixer templates relating to Sonar (or any other sequencer), no MIDI, and no software program for remotely editing aspects of the hardware setup. It's a shame, but perhaps understandable considering the retail price.

Conclusion

Edirol have to be commended for producing a fairly unusual product, which will be valuable both in the studio and certain live situations. Most small mixers of this kind merely include USB as a means of recording the stereo mix, so the M16DX's ability to record all 16 channels, plus the stereo mix, is very interesting. The acoustic analysis tool also works well and offers a fast way to impose a tried-and-tested balance on an unfamiliar acoustic environment, although it remains to be seen how much it actually gets used in real-life situations.

Personally, I'm not wholly convinced by the two-module idea. I can understand that it is sometimes convenient to be able to rack up the I/O and then work with a small desktop control surface. However, instead of having all the I/O situated in one place (as you usually do at the back of a small mixer), it is in three different locations! In my studio this meant that there were leads all over the place.

There are more sophisticated digital mixers on the market, and computer interfaces with better clocking facilities and routing management tools. All this said, I can't think of anything else that offers this particular combination of features, and certainly nothing in this price bracket that delivers 18 channels of audio simultaneously via USB, so there is undoubtedly a market for the M16DX — and possibly quite a large one at that. 

Alternatives

There are plenty of USB and Firewire digital mixers, and some, such as the M-Audio NRV10 reviewed in SOS March 2007, offer multi-channel I/O. However, no alternatives spring to mind that do quite the same job as the M16DX.

Published July 2007