Review: CEntrance MixerFace R4R Mobile USB Interface and SD Recorder

Mobile recording’s popularity continues to grow. Podcasts were already on the upswing before COVID-19 hit, but because of the pandemic, streaming is becoming more common than ever.  Although a lot of streaming involves mobile devices like smartphones and tablets, their audio quality has not kept up with their video quality. Despite the many interface/mixers designed for podcasting and streaming with mobile devices, the options for a premium-quality, self-contained device that’s optimized for mobile applications are limited.

Fortunately, CEntrance’s MixerFace R4R is clearly designed for sophisticated mobile applications. It’s a mixer, high-quality set of preamps, optional SD recorder, and USB interface. MixerFace supports iOS, Android, Mac, Linux, and Windows using USB 2.0, but is electrically compatible with USB 3.1 (USB-C connectors require a physical adapter).

R4 and R4R

The MixerFace R4 and R4R are virtually identical, except that the R4R has a built-in SD recorder. Both models accommodate AC power via a USB adapter (not included), and a rechargeable battery that lasts up to 8 hours (depending on how power-hungry your phantom-powered mics are). Note that you can charge/power with a USB charging port, while a second USB port handles audio. Nice.

Compared to my expectations, the MixerFace is both lighter (under 10 ounces) and more compact (4.75″ x 1.5″ x 2.75″—the ad copy says it’s the size of a passport, but it’s actually smaller). The build quality is clearly field-friendly—this is not something that can’t leave the house. It comes with a felt carry pouch, which protects it from scratches when being jostled around with other gear in a backpack. One of the more surprising aspects is how something that feels so substantial can also feel so portable.

Let’s start with the audio I/O. Each of the two Neutrik mic/line/instrument combo jack inputs (Fig. 1) have Hi-Z and high-pass filter switches, gain controls with LEDs for peak and signal, and a switch that supplies phantom power to both mic inputs. The Hi-Z input is 1 Megohm…a welcome touch for guitar and bass players. A stereo minijack handles the Aux 3 and 4 line inputs, and each channel also has a monitor blend control (i.e., zero-latency monitoring) for the input and USB signal coming back from your mobile device to the MixerFace.

Front inputs
Figure 1: The main inputs are Neutrik combo jacks to accommodate mic, line, and instrument-level inputs. Note the outputs on the sides.

Two TRS minijacks handle the output to powered monitors. There’s also a headphone/monitor output control, low/high line output-level switch, mono/stereo monitoring switch, and pre-monitor 1/8″ stereo line output. Figure 2 shows the R4R’s controls that are opposite from the input jacks.

More controls
Figure 2: This panel incorporates the transport buttons and micro SD card slot (both are for the R4R only), USB audio and charging connectors, and various I/O and switches.

Note that all the switches are recessed, so you can’t hit them accidentally. Cool…apparently someone actually used this before releasing the prototype for production. The MixerFace comes with a tool (like the ones used to open micro SD card trays in smartphones) to move the switches, although something like a paper clip end or toothpick will also work if you lose or forget the tool.

The knobs are small, but rubberized so they’re easy to adjust, and recessed so they poke just far enough above the case so you can adjust them. This bodes well for long-term reliability—if you hit the knobs, I think it would be impossible to damage or break the pot shafts. The case is anodized aluminum, not plastic. The overall vibe is sturdy, professional, and can probably handle unfavorable environments better than I can.

The SD recorder’s transport buttons are rewind, play/pause (or record/stop in record mode), and fast forward. Overall, operation is straightforward—the two Quick Start guides (one for general controls, and one for the recorder) are pretty much all you need to get going, unless you’ve never seen a mixer or audio interface before.


Given the price and the professional orientation, I expected that the preamps would be good, but they’re excellent performers, with a non-existent “sound.” Other than being a little shy on gain (listed specs are up to 53 dB gain, EIN of -127 dB, and THD+N of 0.004%), given the CEntrance lineage I wasn’t all that surprised that the performance equals or exceeds the preamps you’ll find in contemporary audio interfaces designed for studio use.

One very useful recorder feature (aside from being able to record stand-alone, independently of recording into your smartphone or other mobile device) is that when doing a live stream, you can record the results for later editing, archiving, and/or posting for those who missed the live event. Recording time depends on the size of the micro SD card (up to 256 GB). All files are uncompressed WAV files, so you can’t extend the SD card’s recording time by choosing a compressed audio file format. Then again, degraded audio quality isn’t really the MixerFace’s intended design goal.

As a USB interface, you can specify the bit depth (16 or 24 bits) and sample rate (the usual suspects, from 44.1 kHz to 192 kHz). When not using USB, the native rate is 24-bit/48 kHz.

One point that probably no one cares about other than me is that the MixerFace uses a bipolar analog power supply (±7V). This kind of design gives more headroom, and reduces noise by eliminating the need for a voltage divider circuit to create the artificial ground that some circuit designs require with single-ended supplies. The digital supplies are switched-mode types, which you need to multiply the supply voltage up to +48V (and yes, it really is 48 volts) for the phantom power.

And for video, note that the MixerFace can mount to a tripod. You can use the line out with a DLSR camera to record better audio, while recording to the SD card as backup just in case levels weren’t set properly on the camera.


With Android, you can always send audio out to audio in, but it makes no sense to have the MixerFace generate glorious audio that you then send through the smartphone’s 29-cent A/D converter. So, you’ll need an OTG (“on the go,” female USB to male USB) cable to go digital-to-digital, and bypass any questionable analog circuitry. OTG cables typically cost well under $10, and some models include an additional jack so you can connect a USB charger and charge the phone simultaneously.

For iOS, you need to buy Apple’s Lightning-to-USB 3 camera adapter (apparently knock-offs don’t always work; you’ll need to spent $40 for the Apple version). Note that the official adapter has a Lightning jack in addition to the female USB connector, so you can power your iThingie at the same time you’re using it.

With desktop computers, there’s already a USB input, so you just need an appropriate cable. MixerFace works with Core Audio on Mac; for Windows, there’s an ASIO driver on the CEntrance website.


After you add up what this does, as well as the sound quality, MixerFace doesn’t look so expensive after all. Casual podcasting solutions that are comparably priced sometimes offer more bells and whistles, but MixerFace is clearly positioned as a no-nonsense, count-on-it, “I need something I can depend on” solution for people who need to do quality recording in real-world (and sometimes hostile) environments. It also hits a sweet spot of portability, ruggedness, functionality, size, and feature set. There really isn’t anything else quite like it.


Leave a Reply