The USB audio interface is an essential component of home and professional studios. It’s a DAC, but it’s also an ADC (analog-to-digital converter), the opposite of the DAC. In a nutshell, it is a device that records and plays back digital audio. Since USB audio interfaces are designed for professional audio applications, they often include balanced XLR connections, 24-bit or even 32-bit Hi-Res support, and they measure up well. In my opinion, a USB audio interface like the Motu M4 ($269.95) offers great value for money when used as a DAC or even a preamp.
Background: For the past 15 years or so I have used USB audio interfaces made by a company called Motu. They are the logical continuation of Focusrite’s super popular Scarlett series of USB audio interfaces. I used them with my PC to make music, and that’s how the device is marketed: as an audio production tool. I bought the Motu M4 for myself, not to overhaul – it wasn’t in the cards, it never occurred to me. However…
I recently received two high-quality 2-channel devices with balanced XLR connections for review: a Rotel RCD-1572MKI CD player and a Classé Delta Stereo amplifier. But I didn’t have a preamp with similar connections. Instead of looking for one or using the RCA connections and my Denon AVR, I decided to try the Motu M4; he did so well at the task that he inspired me to write this review.
Features and Specifications
It’s a 4-in/4-out device that runs on USB-C power and connects to a PC the same way. It can work autonomously from a USB phone charger. Inside you’ll find an ESS Sabre32 Ultra™ DAC, which is the same DAC you’ll see in high-end audiophile gear. Even the headphone jack taps into this excellent DAC.
The front panel has a pair of XLR + 1/4″ hybrid inputs, a button to adjust the “input monitor mix”, buttons to activate channel monitoring, “power” switches phantom” for microphones, a “monitor” (i.e. volume) adjustment knob and a 1/4″ headphone jack with its own volume control. There is also a level meter for all four input and output channels, making it easy to detect signal clipping.
Look on the rear panel and you’ll find a MIDI in/out port, mirrored RCA stereo outputs and four balanced 1/4″ outputs on the M4. Granted, some functions, like MIDI, won’t be used for l home audio. I only need the pair of rear 1/4″ inputs, plus matching 1/4″ outputs and the USB-C connection for my minimalist 2-channel high-performance audio system.
The hardware specs are what initially prompted me to use an M4 in a stereo system. The device performs admirably in this respect, with a dynamic range of 115dB for the balanced line input and 120dB for the output, figures high enough for the analog I/O that the device is effectively quiet and transparent when placed in the system. .
The DAC, an ESS Sabre32 UltraTM, stands out in spec. It feeds audio directly to the 120dB dynamic range balanced outputs, and the device simply excels at this task. You can use a Motu M4 to convert any PC into a high quality balanced source for your stereo system, whether it’s connected directly to an amp or a preamp/AVR/integrated. Plus, the headphone jack sounds great, at least as long as you’re not trying to drive high-impedance, low-sensitivity esoteric boxes.
Uses
An M4 is primarily used as a USB audio interface for music production. Its inputs are capable of handling everything from condenser microphones to an electric guitar. You can record in very high quality with it, up to 24 bit, 192 kHz. This capability also makes it a viable option for creating hi-res recordings of vinyl records when paired with a quality phono preamp (and that’s where the built-in level meters come in). very convenient).
For 2-channel audiophile purists, the use case of the Motu M4 is its absolute simplicity. When I used it in the recent Rotel RCD-1572MKII CD player review, I used a pair of 10ft 1/4″ XLR cables to make the connection. Why so long? The amp is located between the speakers, but the CD player is stacked in one corner.But, with balanced connections, a 10-foot run is no problem thanks to the inherent noise rejection.
Used as a simple preamp, there isn’t much to do in terms of setup. After connecting the cables, simply press the button on the monitor, which feeds the input directly to the output while allowing volume adjustment. There are no tone controls to worry about, no circuitry to add a subwoofer or anything like that, you get a very pure and minimalist path for the signal to follow. Or if you want to get super advanced and technical, you can scan the input, send it to the PC for any type of processing you can imagine, and read the output, which is exactly what an interface USB audio made for everyday work in a studio!
With non-musicians, the most appealing use case scenario for M2 is as a USB DAC. Of course, it looks and feels totally different compared to high performance consumer audio equipment. I happen to like “pro” audio equipment for its all-pro, no-frills nature. Anyway, in this usage you just plug the M4 into a PC, set it as the default audio, and you’re good to go. And don’t worry if your amp or integrated or receiver only supports unbalanced RCA connections, the M4 has that too.
Another potential use for the Motu M4 is if you want to put together a podcasting rig and use a high quality microphone. This is one of the main purposes of a USB audio interface like this, with the right microphone it will give your voice a “professional broadcast” quality sound. And if you’re singing, well, a good vocal mic and a Motu M4 are pretty much enough.
Performance
That’s pretty much nothing to report here, and I mean that in the best possible sense. I put this little kit between a $1100 CD player and a $13,000 amplifier, powering a pair of $6600 Focal Aria K2 936 speakers, and the Motu M4 just disappeared.
The sound delivered by the 2-channel rig had all the depth one expects from a big budget system that is largely free of any technical constraints, there are no “weak links” in the chain, the electronics are in the same ballpark – apart from the amazing 1Hz to 650,000Hz bandwidth of the Classé Delta Stereo amplifier, that’s overkill! The thing is, the backdrop to everything I listen to with the Motu in the system is complete silence.
Practical listening encompassed a wide variety of music and, beyond music, recorded sounds. I’ve used the M4 to stream hi-def/hi-res music from Tidal and Amazon. I’ve also used it to play CD quality files ripped to a hard drive. And since I’ve been producing music, I’ve used the Motu to mix and master the tracks I create with Ableton Live software. I even use the Motu to plug in a high quality microphone that I use for web meetings, like Zoom.
The moment that convinced me to go ahead and write this review was when I auditioned CDs with the Rotel, allowing the M4 to act as a simple analog preamp.
Please see the Rotel RCD-1572MKII CD player review to hear impressions of a system with the Motu M2 in the signal path.
Rather than go through a bunch of listening experiments here, I’d like to refer you to the Rotel CD player review, where you’ll find ratings on a variety of different albums, all of which went through the M4 on the path of the Stereo Delta Amplifier.
Admittedly, the performance of the M4 didn’t surprise me, as I already knew it was a great sounding device, when used as a USB DAC. When creating music, I plug in a pair of Audeze LCD-2 closed-back headphones that bring out layer upon layer of detail. It’s not the most powerful headphone amp in the world, or anything like that, but what it can do with a good pair of cans just adds to its value, especially because it’s essentially portable (at throw in backpack or laptop bag, not pocket laptop). The surprise was simply how immediately usable it is, directly in the role of a super simple analog preamp.
There are, of course, clichés about how good this or that awesome audio kit makes the system sound. But ultimately, the goal is to leave the signal alone, as unaltered as possible as it progresses. And if successful, what you hear – assuming sufficient skill on the part of the artist and production team – should qualify as audio epicurean delight, a performance zone where the artists’ intent is delivered in a goosebumps fashion.
Conclusion
The Motu M4 performs exactly as advertised and is therefore a sturdy and affordable piece of kit. It is surprisingly adaptable thanks to its professional applications as a recording device. Performance-driven engineering is what makes the M4 an attractive solution for home audio applications where a high-quality dedicated DAC with balanced connections is desired.
Motu is a brand that has served me well for a decade and a half, so there’s a lot of hands-on personal experience to go along with my recommendation. I also browsed through the whole range of similar devices, especially the best-selling Focusrite Scarlett series. These devices are extremely similar in nature, but model for model IMO, the latest Motus has a performance advantage (a measurable edge, FWIW).
M4 hardware is reliable, functional and well designed. Performance is measurable and verified and of course the proof is in the pudding: you can put an M4 in a high priced, high performance “high resolving” system, it will immediately disappear and, paradoxically, make its presence known through this clarity, because when it comes to high fidelity audio reproduction, in a very real sense, that is what is not there it counts. And in this case, what is not there is the slightest distortion or degradation of the sound that passes through this handy little box. It’s an editor’s choice and it’s also my choice.