Review: Keith McMillen K-Mix Audio Interface, Digital Mixer & Control Surface

K-Mix from Keith McMillen Instruments is a high-quality audio interface, programmable mixer, and MIDI controller combining their best tech know-how in one portable package. Timo Preece gets hands on.  

What if someone was to build a quality audio interface, stand alone mixer with built-in DSP, and a MIDI controller all in one small, rugged package? Keith McMillen and crew realized the need for this very special device that did not exist — a fully programmable, MIDI-controlled, ultra high-quality portable mixer for studio and stage. I’ve had this little unit on my desk now for a couple weeks and I must admit, it has a lot to offer…

Check out AskAudio’s initial announcement for a quick look and tech specs here.

Renewed Hands-On Control

My initial reaction when hearing about the K-Mix was slightly underwhelming as I reflected on reasons behind abandoning mixers in my personal setup altogether. They take up space, aren’t very portable with the amount of gear I need to carry while touring, and have been something I’ve replaced with ‘in the box’ digital routing.

With that being said, I acknowledge the limitations of my setup… I have little to no tactile control on the interface itself. Without a separate MIDI (or OSC) controller assigned to the mix software, I’m forced to use a mouse to make adjustments, which only allows me to navigate one parameter at a time. Although my interface can be used standalone, there is only one knob on the unit to control all associated parameters. 

Keith McMillen K-Mix

Keith McMillen K-Mix

Admittedly, such limitations are not optimal for mixing. After spending time with the K-Mix, appreciating renewed hands-on control, something clicked… there’s a discernible distinction between ‘mixing’ and ‘routing’.

One Tight Package

In my humble option, one of the greatest advantages of the K-Mix is the amount of quality and functionality you get for its size. It’s no bigger or any heavier than a standard portable audio interface. It’s built rugged with absolutely no moving parts, which means I can toss it in a backpack and hit the road with little worry about it getting damaged. (By the way, did I mention that the only knob on my audio interface is somewhat broken and mostly unusable after much tweaking and many a travel?)

K-Mix faders have been remodeled from the ground up. Unlike the KMI QuNeo for example, I haven’t experienced the same jumpiness that occurs while making parameter changes. Instead, the controls are responsive and smooth to the touch. For added control, there’s a Fine Tuning mode that allows you to “zoom in” on a fader or rotary control, providing a much higher degree of resolution than under “normal” operation.

Audio Interface—Ins and Outs

As advertised, K-Mix is a pro-quality USB audio interface with 2 ultra-low-noise, transparent µPre™ preamps for quality recording. Supporting sampling rates up to 96 kHz and 24-bit AKM Converters, you get 8 balanced inputs and 10 outputs (8 balanced). 

Back of the K-Mix

Back of the K-Mix

Inputs 1 & 2 on K-Mix feature two XLR/TRS combo jacks for connecting microphones via XLR connectors or line level and instrument level signals via 1/4” TRS connectors. Inputs 3–8 on K-Mix feature 1/4” TRS jacks. These allow for connecting balanced (or unbalanced) line level and phono level signals via 1/4” TRS connectors.

Each of the 8 input channels has an optional high-pass filter at the beginning of the DSP chain. This is intended to be used as a “rumble filter”, removing microphone handling noise or the “thump” that may occur when bumping a turntable.

Regarding outputs, K-Mix offers 8 1/4” TRS Connectors (balanced) and 1 stereo 3.5mm TRS headphone output. Outputs are grouped into stereo output “busses” or “bus pairs”—the main output bus, three aux output bus pairs, and the headphone output bus.

Headphone setup screen

Headphone setup screen

Outputs 3–8 are K-Mix’s “auxiliary outputs”, or “aux outs”. These six outputs are split into three stereo pairs, Aux 1, Aux 2, and Aux 3.

  • Aux 1 = outputs 3–4
  • Aux 2 = outputs 5–6
  • Aux 3 = outputs 7–8 

Surround All Around

Another happening feature is K-Mix’s ability to leverage multiple outputs and rotary controls to spatialize audio in multiple surround sound formats. The software editor allows a user to switch between Quadrophonic, Octophonic, 5.1 and 7.1 configurations. Moreover, K-Mix utilizes Ambisonic panning algorithms to ensure a high-quality soundstage when working in a surround sound environment. 

There’s an added Bass Management feature with a low frequency crossover setting. Employing such routes low frequency content out the headphone jack; higher frequency content will go out outputs 1–8 as normal.

Surround Sound Setup screen

Surround Sound Setup screen

Onboard DSP

The K-Mix comes equipped with its own set of DSP effects. This is a welcome addition for those wanting to use K-Mix as a standalone mixer or those needing to save valuable computer resources.

The Master output and each of the 8 channels get their own dynamic processing chain, which consists of a 3-band semi-parametric equalizer, compressor and noise gate. K-Mix also offers a global reverb effect send. Each of the 8 input channels can route to the reverb at different levels using the available reverb sends. Reverb sends can be set pre-fader or post-fader and all reverb parameters can be controlled via the mixer hardware or the software editor.

Note: Unlike the main output bus, the auxiliary outputs do not have any DSP effects and the reverb send effect is not mixed into the aux outputs.
Channel Strip setup

Channel Strip setup

Reverb screen

Reverb screen

MIDI Control

In addition to functioning as both a mixer and audio interface, K-Mix speaks MIDI. 

K-Mix allows for bidirectional MIDI communication with USB host devices (computer, tablet), and with external MIDI hardware (via the optional KMI MIDI Expander). K-Mix is fully capable of both outputting MIDI to control other devices/software, and receiving MIDI for control of its own parameters. Each sensor can be set to output a different MIDI message for each of the three available MIDI banks.

MIDI Panel

MIDI Panel

At the time of writing this article, sending MIDI information via USB connection to my computer worked nicely and I was able to MIDI map values from the K-Mix to my DAW. However, as indicated in the manual, several features are still under development. One of which is control surface mapping to applications such as Ableton Live. After speaking with KMI’s technical support, they’ve assured me it’s in the works and for the mean time there’s a user script workaround. 

“Using the UserConfiguration.txt file can quickly provide a way to play with devices and control the faders in Ableton Live right from our K-Mix with zero MIDI mapping. This lacks some of the more advanced features of a full blown Remote Script. Users won’t have LED feedback, and won’t have the ability to access different banks or pages on one preset, but will still be able to get some decent integration.”

Link to more details, instructions and the UserConfiguration.txt file here.

Wrap Up

With the popularity of outboard gear continuing its resurgence, connecting and managing external sources necessitates a special set of needs. If you’re looking for a quality, portable, rugged audio interface, mixer, controller at a respectable price, this is a great choice.  

Price: $579.00 USD MRSP

Audio Interface

  • USB Bus Powered
  • Ultra-Low Noise µPre™ Preamps
  • High-End AKM Converters
  • 32-bit Floating Point Signal Path
  • 8-in/10-out Audio

Programmable Mixer

  • Per Channel DSP
  • Flexible Routing
  • Standalone Quad 5.1, 7.1 and Octophonic Surround Mixer
  • Onboard Preset Storage
  • No Computer Required

Control Surface

  • Ultra-Sensitive Precision Rotaries and Faders
  • User Assignable MIDI Controls
  • Light Weight and Portable
  • Rugged Construction, No Moving Parts


  • Lightweight, portable, rugged audio interface, mixer, control surface.
  • Standalone or computer controlled operation.
  • Buit-in onboard DSP
  • Surround layouts and bass management
  • Great quality for the price
  • Turntables can be directly connected to the K-Mix


  • On my system, K-Mix editor version 1.0.11 would sometimes drop connection requiring the mixer hardware to be powered off and on and the editor relaunched (this glitch did not affect the hardware mixer’s functionality… only the editor was affected).   
  • Control surface mapping and several other MIDI features are still under development (i.e. MIDI Expander Input)
  • iOS integration working with certain software but not all. Official support should be coming soon. 
  • Window’s operating systems not currently supported. However, KMI is actively working on Windows support and hope to have that released soon.


Timo Preece (Certified Ableton Trainer, ProTools Expert) is an accomplished audio technologist, multi-media consultant, sound designer and electronic musician. He graduated with a degree in Ethnomusicology from UCLA and a Masters in Sound Design at the University of Edinburgh, UK. From conceptualizing and building cutting-edge setu... Read More


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