Review: Keith McMillen Instruments K-Mix

Compact audio interface, control surface, and mixer for Mac OS.
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Although there are digital interfaces and controllers of practically every size, shape, and application on the market, nothing compares to Keith McMillen Instruments’ K-Mix in terms of versatility, features, build quality, and visual appeal. In addition to working as a controller (with an “opto-tactile” control surface, found on many of KMI’s other products), the K-Mix is also an 8x10 USB audio interface and programmable mixer with internal effects. And despite its diminutive, desktop-friendly size—3.5 lbs., 9.7" x 6 1/2"—it can be integrated into a pro-level recording system or work as the hub of a P.A. system for live performances, away from the computer (see Figure 1).

Fig. 1. The KMI K-Mix packs a tremendously versatile feature set into a small package. The K-Mix supports 24-bit audio with sampling rates up to 96 kHz. It connects to a computer via USB 2 that passes both audio and MIDI data. A mini-USB port is also provided for the included 5V power supply or for connecting the optional KMI MIDI Expander ($59) so you can address external MIDI hardware. For standalone operation (away from a computer), you’ll need to use the power supply with the K-Mix.

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I tested the K-Mix in standalone mode as well as with MOTU Digital Performer and Ableton Live using a quad-core 4GHz, iMac 5K Retina using Mac OS X 10.11.4 (OS X 10.6 or later is supported). I also tested the K-Mix with an iPad Pro, although at the time of this writing iOS is not officially supported. (However, the K-Mix works with any generation of iPad and requires either a USB-to-30-pin camera adapter for older iPads or a Lightning-to-USB adapter for recent models.) At present, the K-Mix is not compatible with Windows OS, although it is in development.



Fig. 2. K-Mix offers a generous amount of analog I/O, and the outputs can easily be configured for surround applications. Inputs 1 and 2 accept mic-, line-, and instrument-level input. The K-mix’s analog I/O is remarkably generous for such a compact device. Of the eight balanced inputs, channels 1 and 2 have combo jacks that accommodate XLR mic-level signals, 1/4" TRS line-level input, and high-impedance instrument input from 1/4" TS cables (see Figure 2). Inputs 1 and 2 also include KMI’s new ìPre mic preamps, which offer two levels of phantom power: +48V and +12V. KMI spent a great deal of time on its custom mic preamps, and it shows. And in terms of the instrument inputs, I heard much clearer high-end articulation on my electric guitars, evenly balanced with their lower-end frequencies. Inputs 3 through 8 accept 1/4" TRS plugs only, but they can handle line-or phono-level input to accommodate turntables.

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The K-Mix provides eight analog outputs on balanced 1/4" TRS jacks, with outputs 1 and 2 serving as the main monitor outs. The stereo headphone jack on the front of the unit can also be pressed into service as a low-frequency speaker output when the K-Mix is used in a surround sound configuration. Quad, 5.1, 7.1, and octophonic speaker configurations are supported, with Ambisonics panning algorithms used to create the multichannel soundstage.

Fig. 3. You’ll need the K-Mix software editor to set up surround parameters, create presets, and access other functionality. Surround mixes are configured using the KMix Editor software (see Figure 3). Click the Bass Management button in the software to set the headphone output’s adjustable crossover for low frequencies. Each of the four buses will display a marker, which serves as a visual aid detailing ideal positions for each of the eight possible speakers. The rotary encoders on the K-Mix reflect surround moves; as you move the signal along the periphery of the circle, a red dot on the controller will follow. As you move the signal toward the center, the dot switches to an illuminated ring around the encoder’s circumference, reflecting the signal’s distribution among the other buses.

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When mixing, I was impressed by the clarity and apparent extended headroom of the audio, even at higher volumes than I am accustomed to using when monitoring. Dense mixes with a variety of virtual instruments maintained the distinct sonic characteristics of each element without the typical “pad soup” that can occur.



With the exception of the power button, everything on the K-Mix provides layers of functionality. The four rotary knobs, ostensibly for controlling pan position in a mix, can serve a remarkable number of additional functions, depending on the mode of operation. For instance, if you are editing reverb settings, the rotary encoders control (from left to right) pre-delay, damping, diffusion, and decay, indicated by a bright blue LED circumnavigating the lower portion of each rotary. When in MIDI Mode, you can use the encoders to adjust plug-in parameters.

When used in conjunction with the Shift button, the diamond-button pad to the right of the encoders shunts K-Mix between normal mixer and MIDI controller chores: The left diamond button accesses mixer functions, and the remaining buttons choose between three banks of MIDI assignments. The diamond pad is printed with common transport icons because the buttons can easily be set up as transport controls for any DAW; in MOTU Digital Performer 9.3, it merely required making the change in the program’s control surface assignments.

Above the nine faders is a set of channel-select buttons that can be used to check solo, mute, or bypass status; apply phantom power; choose which channels to monitor through the headphones; edit pre-or post-fader sends; and bypass effects, among other things. And, as you would expect, the faders can also perform multiple functions—track volume, input trim, effects-send level, and the transmittal of MIDI Continuous Controller messages.

The faders bear singling out as one of the KMix’s major highlights. Each fader has a smooth and continuous feel under the finger, with green, yellow, and red LED segments that show fader position or audio level in VU metering mode. Because the touch surface is so responsive, it can be used for tapping in values to get sudden changes: In MIDI mode, that can be useful for creating radical timbre shifts when using synth plug-ins or filter effects.

The four vertically arrayed buttons to the left of the faders—Shift, Bypass, Fine, VU—work in conjunction with other K-Mix functions. For example, holding the Shift key while pressing the record symbol on the diamond buttons engages KMix’s MIDI Controller functionality. Shift can also access additional DSP parameters as well as toggle the solo and mute status of the faders. The Bypass button enables or disables effects, per channel or globally. The Fine button increases fader and rotary resolution, allowing you to dial in parameters more precisely.

A dozen multifunction buttons also sit to the right of the faders. In Mixer and Interface modes, they engage a variety of functions such as monitoring the Mains or the three Aux outs or assigning gate, reverb, pan, EQ, and trim for each channel. In Controller mode, they can be used to gain access to banks of MIDI presets. The text describing each button’s function is small, and although the backlighting helps, they can be hard to discern when they are not selected. Although this can become more problematic in dimly lit venues, a bit of memorization (or a new eyeglass prescription) goes a long way.

The built-in effects—reverb, noise gate, compressor, low-cut filter—sound great and are straightforward and relatively simple to use. Moreover, each of the eight input channels, as well as the main output bus, has 3-band semi-parametric EQ.



The K-Mix integrated nicely with Digital Performer. As I mentioned earlier, the transport was easy to set up. Setting up the trim for each track was equally simple; hit the Trim button, then the Track Select button, and adjust the input level. In Trim mode, the color-coded LED provides a reliable visual index for maximizing input without clipping. Reverb and other DSP functions are set to pre-fader by default, so if you want to apply effects to synth plug-ins or pre-existing tracks, you will need to use the K-Mix Editor application. While many such functions are only available from the software editor, you can save your settings as presets.

In MIDI Mode, editing and animating plug-ins, especially using the DAW’s MIDI Learn feature, was fairly straightforward. The K-Mix makes it easy to edit multiple parameters on-the-fly. However, controlling Digital Performer’s channel faders was not nearly so simple, and required MIDIPipe as a go-between app.

I followed KMI’s online video tutorial for assigning fader controls in Ableton Live 9.6 and was quickly rewarded: The K-mix’s faders imparted a graceful, tactile feel to the virtual controllers.

Though it not might be the most obvious method for triggering sounds, the K-Mix’s buttons can also send MIDI Note-On messages, and in a pinch, you could map the note output to trigger drum sounds. MIDI notes are by no means the only possibilities, however; the software editor’s control panel lets you program other useful MIDI messages. In fact, changes made to parameters in the software are reflected on the hardware and viceversa. The editor lets you store and name presets, check for and implement firmware updates, assign pre-or post-fader status to tracks and effects, and lots more. Of course, you can use it to set up presets for standalone mixer operation, too.



Integrating K-Mix with my iOS apps was not quite so simple, largely because the platform is not yet officially supported or documented by KMI. Although Apple GarageBand, Propellerhead Thor, and Korg Gadget LE showed few problems with audio I/O, use as a MIDI controller remained undiscovered territory for me. In order to communicate with my iPad, I used an Apple Lightning-to-USB camera adapter, which connects to the USBmicro port on the K-Mix. Because the iPad doesn’t dispense enough power to drive K-Mix, I plugged the power supply into the USB Control port.

Nonetheless, developers at KMI told me that it is focusing its attention on full iPad compatibility for the K-Mix, and I’m optimistic about seeing thorough documentation and official support in the near future.


The K-Mix is in a class all its own and is easily the most playable non-keyboard controller I’ve used. What other device can you think of that combines a USB 2 audio/MIDI interface offering an 8-in/10-out surround capable mixer and DSP effects, coupled with a unique multicolored touch controller that can operate with or without a computer? And while I wouldn’t deliberately drop it, I am confident that the K-Mix is rugged enough to withstand the rigors of live performance, in part due to K-Mix’s build quality and complete absence of moving parts.

Other than the lack of Windows OS support, it is difficult to find anything negative to say about the K-Mix in light of the tremendous amount of functionality it packs into such a small frame. Forthcoming updates will include, among other things, the option to increase backlighting incrementally and the addition of a signal generator with adjustable frequency (40 Hz to 4 kHz).

And as powerful as it is for music on the Mac, I see the K-Mix as a very promising work-in-progress for the iOS platform. Adding the optional MIDI Expander enhances the K-Mix’s functionality with the iPad, where the single Lightning input would normally preclude use as an external MIDI controller.

If you are looking for a control surface, a surround-capable audio interface, and a digital mixer with DSP, K-Mix gives you an extraordinary, affordable combination of all three.


Enormous versatility. Draws power from a computer, power supply, or powered USB Hub. No moving parts. Tactile controls. Great sounding preamps.


The small buttons can be difficult to read. Windows not supported. iOS not officially supported.


Contributing editor Marty Cutler has not yet decided on a running mate.