MOTU M4 Review: Specs, Features and Who It Suits

As an Amazon Associate I earn from qualifying purchases. This write-up is based on MOTU’s published specifications and documentation, not hands-on testing.

The MOTU M4 is a 4-in, 4-out USB-C audio interface that adds two balanced line inputs, two extra line outputs and an input monitor mix knob to the two combo mic/guitar preamps, 120 dB output dynamic range and color LCD metering of its smaller sibling. Those extras make it a better fit for producers who connect a keyboard or synth alongside mics, or who need a second pair of outputs for another set of speakers or a headphone amp.

See the MOTU M4 on Amazon.

MOTU M4 key specs

Mic/guitar inputs	2 XLR/TRS combo jacks with independent gain, 48V and MON switch
Line inputs	2 rear 1/4″ TRS (balanced or unbalanced), 115 dB dynamic range, +18 dBu max
Line outputs	4 balanced 1/4″ TRS (DC coupled), 120 dB dynamic range, +16 dBu max
RCA outputs	4 unbalanced, mirroring the TRS outs
Headphones	1 stereo 1/4″ output with separate level
Front controls	Monitor and phones volume, input monitor mix knob, 3-4 switch
Mic EIN	-129 dBu
MIDI	In and out
Sample rates	44.1 to 192 kHz
Display	Full-color LCD (160 x 128) for input and output levels
Power and bus	USB-C, USB 2.0 class compliant, bus powered
Dimensions	20.955 x 10.8 x 4.5 cm, 0.7 kg

Source: MOTU M4 tech specs and the M4 product overview.

What the M4 adds over the M2

Both models share the same preamps, converter technology, metering screen and bus-powered design. The differences are all about connections and monitoring control:

• Two dedicated line inputs on the rear, so a stereo keyboard or drum machine can stay plugged in while both front preamps remain free for a mic and guitar. All four inputs can be recorded at once.
• Outputs 3-4, a second balanced pair (plus mirrored RCA). The front-panel 3-4 switch relates to how these outputs are used for monitoring; check MOTU’s documentation for exact behavior.
• An input monitor mix knob that blends live inputs against computer playback, which MOTU describes as controlling the balance between the two.
• A slightly wider and heavier metal case to fit the extra jacks.

Read our MOTU M2 write-up if two inputs and two outputs are enough for you.

Why a monitor blend knob matters

When you track vocals or guitar with direct monitoring, you need to hear yourself and the backing track at a comfortable ratio. Without a blend control, you adjust the playback level in software and hope the balance works. The M4’s knob lets the performer change that ratio instantly from the front panel, which helps when you are recording yourself and cannot easily reach the mouse.

Using four outputs

Four line outputs open up several setups that a two-output interface cannot handle as neatly:

• Two pairs of studio monitors, such as main speakers and a small reference speaker, to check mixes on different systems.
• Sending a separate cue mix to an external headphone amplifier.
• Routing to outboard effects and back through the line inputs, using the extra outputs as hardware sends.
• Feeding a DJ mixer or PA via the RCA outputs.

Measured performance claims

MOTU’s published numbers put the line outputs at 120 dB dynamic range with -110 dB THD+N, the line inputs at 115 dB with -106 dB THD+N, and the mic preamps at -129 dBu EIN. MOTU attributes the output figures to ESS Sabre32 Ultra DAC technology, which also drives the headphone amp. Spec sheets cannot tell you how an interface sounds to your ears, but these figures put the M4 among the quieter small interfaces on paper. Our guide to mic preamps explains what EIN measures.

MOTU also quotes 2.5 ms round-trip latency at 96 kHz with a 32-sample buffer. Your own results will depend on your computer and session.

Loopback, drivers and platforms

As with the M2, the M4 driver includes loopback channels for mixing computer audio with live inputs, a common need for streaming. The interface is class compliant on Mac and iOS (iOS requires an adapter and, per MOTU, a powered USB hub), and uses a MOTU driver on Windows. See our guide on how to use an audio interface for setup basics.

Bundled software

MOTU includes Performer Lite, Ableton Live Lite and a library of loops and one-shots. Bundles can change, so confirm on MOTU’s site.

Who should buy the MOTU M4

• Producers with a keyboard or synth who also record vocals or guitar.
• Home studios with two sets of monitors.
• Performers who want a hardware blend between input and playback.
• Streamers who need loopback plus extra line inputs for other sources.

Who might choose something else

• Recording more than two mics at once needs an interface with more preamps.
• Two separate headphone outputs for two performers are not on the M4.
• No ADAT or S/PDIF, so there is no digital route for expansion.

For a rack-sized alternative with more preamps, compare our PreSonus Studio 68c write-up. Our guide on how to choose an audio interface helps weigh inputs, outputs and monitoring.

How to set up the MOTU M4 step by step

Getting clean, low-latency audio from the MOTU M4 takes about ten minutes. The order matters, because driver and buffer choices affect everything after them. Follow these steps before you record your first take.

1. Install the right driver. On Windows, install MOTU’s driver before you plug in the interface. On a Mac, the M4 works without a driver, but MOTU offers an optional one. Download both from MOTU’s support pages.
2. Connect with the supplied cable. Plug the M4 into a USB-C or USB Type A port. It is bus powered, so no wall adapter is needed. Avoid unpowered hubs, since they can starve the unit of power.
3. Select the M4 in your DAW. Open your audio preferences and choose the M4 for both input and output. On Windows, pick the MOTU ASIO driver rather than a generic one.
4. Set the sample rate. 44.1 or 48 kHz suits most music and video work. Higher rates up to 192 kHz are supported, but they use more processing power and disk space.
5. Choose a buffer size. Start at 64 or 128 samples while tracking. Raise it to 512 or 1024 when mixing with many plug-ins.
6. Turn the monitor knobs down. Lower the monitor and phones levels before you power your speakers. Then raise them slowly.

Once these basics are set, test each input with the LCD meters before you press record.

Setting gain with the color LCD

The full-color screen is one of the M4’s most useful tools. It shows levels for every input and output at once. That means you can set gain without staring at your DAW.

First, ask the performer to play or sing at their loudest. Next, turn the gain knob until the meter peaks well below the top. A safe target is roughly -12 to -6 dBFS on the loudest parts. That leaves headroom for surprise peaks. If a meter reaches the top, the signal is clipping, so back the gain off.

Line inputs 3-4 have no gain knob. Instead, set the level at the source, such as the volume on your keyboard. Our guide to using an audio interface covers gain staging in more detail.

Monitoring: hardware vs software

The M4 gives you two ways to hear yourself. Each has a clear use, so pick one per session.

Hardware (direct) monitoring sends the input straight to your headphones. Press the MON switch on the input you want to hear. Then use the input monitor mix knob to balance it against playback. Because the signal never passes through the computer, there is no latency to notice. However, you will not hear plug-ins such as reverb or amp sims on the input.

Software monitoring routes the input through your DAW. As a result, you can hear effects while you record. MOTU quotes 2.5 ms round-trip latency at 96 kHz with a 32-sample buffer. Real results depend on your computer and session size, though.

Never use both at once. If MON is on and your DAW track is also armed for monitoring, you will hear a doubled, phasey signal.

A sample session: synth plus vocal

Here is a practical setup that shows why the M4’s extra inputs matter. Picture a producer recording a stereo synth and a vocal in one pass.

• Plug the condenser mic into input 1 and switch on 48V phantom power.
• Connect the synth’s left and right outputs to rear line inputs 3 and 4.
• Leave input 2 free for a guitar or a second mic later.
• Create a mono track for input 1 and a stereo track for inputs 3-4 in your DAW.
• Turn on MON for input 1, then set the blend knob so the vocal sits just above the track.

With this layout, nothing needs re-patching between takes. That speed is the main reason to choose the M4 over a two-input box.

Using loopback for streaming and podcasts

Loopback sends your computer’s own audio back in as a recordable input. For instance, a streamer can mix game audio, a browser call and a live mic in one program. To use it, select the M4’s loopback channels as inputs in your streaming or recording software. Then mute any track that would feed loopback back into itself. Otherwise, you can create a feedback loop.

MOTU M4 vs similar interfaces

The M4 sits in a crowded class. This table compares it with close alternatives, using each maker’s published specs.

Feature	MOTU M4	MOTU M2	Focusrite Scarlett 4i4	PreSonus Studio 68c
Mic preamps	2	2	2	4
Extra line inputs	2 rear TRS	None	2 rear line	None (combo inputs)
Line outputs	4 TRS + 4 RCA mirrored	2 TRS + 2 RCA mirrored	4 balanced	Main + outputs 3/4
Headphone outputs	1	1	1	1 (Cue A/B)
Digital I/O	None	None	None	S/PDIF in/out
MIDI	In/out	In/out	In/out	In/out (breakout)
Power	USB bus	USB bus	USB bus	12V adapter
Metering	Color LCD	Color LCD	Gain halos	Front-panel meters

In short, the M4 is the pick for line inputs plus clear metering. The 68c suits anyone who needs four mic preamps and S/PDIF instead.

MOTU M4 pros and cons

Pros

• Four simultaneous inputs, with two kept for line sources.
• 120 dB dynamic range on the main outputs, per MOTU.
• Color LCD shows every input and output level at a glance.
• Hardware monitor blend knob for latency-free tracking.
• Bus powered and housed in a metal case, so it travels well.
• Loopback built into the driver for streaming.

Cons

• Only two mic preamps, so drum or band recording is limited.
• One headphone output, which makes two-person sessions awkward.
• No ADAT or S/PDIF for adding preamps later.
• No built-in DSP effects for monitoring.

Routing outputs 3-4 in your DAW

Outputs 3-4 do nothing until you send audio to them. Most DAWs let you assign any track, bus or the master to a chosen output pair. Here are three common setups.

• Second speaker pair. Duplicate the master to outputs 3-4. Then mute one pair at a time to compare speakers. Some DAWs and monitor controllers make this easier with a speaker switch.
• Headphone cue mix. Create a send bus routed to outputs 3-4 and connect a headphone amp. Now a second performer gets their own balance.
• Hardware insert. Route a track out of 3-4 into a pedal or compressor. Next, return it to line inputs 3-4 and record the result.

Label the outputs in your DAW’s I/O setup. Clear names save time and stop you sending a mix to the wrong place.

Buffer size cheat sheet

Buffer size trades latency for stability. Smaller buffers feel tighter but strain the computer. Larger ones are stable but add delay. Use this table as a starting point, then adjust for your machine.

Task	Suggested buffer	Why
Tracking vocals with software effects	32-128 samples	Keeps delay low enough to sing in time
Playing virtual instruments	64-128 samples	Notes respond quickly to your keyboard
Tracking with MON direct monitoring	256 samples	You hear the input directly, so delay matters less
Mixing large sessions	512-1024 samples	Frees processing power for plug-ins

If you hear clicks or dropouts, raise the buffer one step. Also close other apps that use audio, such as browsers or video calls.

For more context on connections, see MOTU’s official M4 page, which lists the full I/O and system requirements.

Common mistakes

• Plugging a keyboard into the front preamps by default. On the M4 the rear line inputs keep the preamps free for mics.
• Leaving the monitor mix knob fully toward input. You will not hear the backing track and may think playback is broken.
• Assuming outputs 3-4 carry the main mix automatically. Check routing in your DAW and MOTU’s documentation.
• Running iOS without enough power. MOTU recommends a powered USB hub for iOS.
• Using a generic Windows driver. Install MOTU’s ASIO driver, or latency will be much higher.
• Tracking at a huge buffer. A buffer of 1024 samples makes software monitoring feel laggy. Drop it while recording.
• Doubling the monitoring. Use MON or DAW input monitoring, not both.

FAQ

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