Comparing original and current MOTU M2 USB audio interfaces

We previously reviewed the two-channel MOTU M2 USB interface. This distinctive product from American engineers quickly became a bestseller. Excellent electronics and attractive meters on a small colour display set the MOTU M2 apart. Global component shortages, especially XMOS microcontrollers and AKM converters, forced a change of suppliers. Current M2 units therefore use an ARM processor and ESS converters. Buyers worried that these changes might reduce quality. We can now compare original and updated versions directly, which is the purpose of this review.

First, appearance. Careful inspection of the case, knobs and sockets found no differences. Both have the same strong aluminium case, Amphenol connectors and digital encoders for gain, master volume and headphones. The colour LCD has a slightly different tint: bluish on the original and whiter on the new unit. This may be specific to our samples. Knobs turn identically with light, pleasant resistance. Paint and lettering quality are equally high. The box and included accessories are unchanged. We found no external differences that should concern users.

MOTU M2/M4 specifications

Despite updated electronics, MOTU M2/M4 specifications are unchanged. This is good news.

The important differences are inside.

A 32-bit processor replaces the XMOS microcontroller: Cortex-M7 ATSAMS70N20 ARM processor, which we previously saw in the MOTU UltraLite MK5. Communication still uses USB 2.0.

The excellent 8-channel ES9016S DAC, with 124 dBA dynamic range and -110 dB THD+N, has been replaced by an 8-channel ES9026PRO with the same 124 dBA and -110 dB figures. The reason is simply that ES9016S production has ended. Both chips have equivalent specifications. Both MOTU M2 generations specify 120 dBA output dynamic range.

The former 2-channel AK5552 ADC (115 dBA dynamic range, -106 dB THD+N) has been replaced by a 2-channel ESS ES9820Q (116 dBA, -108 dB). Performance has certainly not become worse. Both versions measured exactly 115 dBA input dynamic range. TRS input distortion is identical and depends on the unchanged preamp rather than the ADC. Frequency response differs slightly. At 20 Hz, the original M2 drops -0.1 dB, while the new one drops -0.6 dB. This comes from the necessary filter that blocks DC at the ADC input.

Both MOTU M2 generations use the proven American THAT 6263 digitally controlled integrated chip. It combines a microphone preamp, controller and ADC buffer. Gain covers -8 to +34 dB.

The headphone output retains the OPA1688 op-amp, specified at 50 mW into 32 ohms with low distortion. That may seem modest, but some budget interfaces provide 10 times less power. Here there is enough volume even for high-impedance headphones. The 3.3 V RMS signal gives fairly good sound with Beyerdynamic 990 PRO headphones, without audible problems.

Drivers are unchanged. Both units work well simultaneously in one system with the same driver and identical control panels. Firmware differs, of course, but users see no functional differences. Software I/O counts are unchanged. Operation is stable, as expected from MOTU, with no unusual issues.

The useful Use lowest latency checkbox enables or disables an extra buffer, choosing faster signal transfer or greater stability.

With this option, round-trip latency is a good 6.2 ms at a 64-sample buffer.

Small buffers and fast signal transfer matter for real-time processing, such as playing a MIDI keyboard or processing guitar.

ASIO diagnostics

The ASIO driver's most interesting features are Loopback and Loopback Mix. These virtual channels broadcast sound from all inputs and outputs over the internet.

RMAA PRO measurements

Both interfaces were measured under identical conditions. They were connected simultaneously to the same laptop and USB port, with the laptop on battery power. We show only RCA line-output measurements, but balanced TRS results are very similar.

Updated MOTU M2 measurements at 24-bit/44 kHz are on a separate page.

Differences between measured figures are extremely small. Every test result is excellent.

For easier comparison, the graphs overlay original and updated MOTU M2 results:

Frequency-response graphs are identical.

Noise graphs are identical.

Dynamic-range graphs are identical.

The updated version has slightly lower harmonic distortion.

The updated version has slightly lower SMPTE intermodulation distortion.

The updated version has slightly lower CCIF intermodulation distortion.

We found no operational changes. All M2 knobs remain digital, with fixed 1 dB steps. This suits human loudness perception and is convenient. Digital encoders should last longer than potentiometers, whose channels can be mismatched and which can become noisy over time. These encoders have end stops and position marks. They allow exact matching of input and output levels.

As before, peak meters show digital signal levels before the controls, independently of line-output knob positions. Decibel markings beside the knobs, as on inexpensive mixers, would be useful.

The interfaces have no processing, low-cut filters or EQ. All further software processing takes place in a DAW. Light versions of MOTU Performer and Ableton Live are supplied, along with sounds and effects.

We recorded voice through a Neumann TLM103 into both interfaces. Both gave excellent results. The original M2 with AKM ADC has a slightly warmer voice tone; the updated M2 with ESS ADC reveals slightly more detail. The difference is tiny because the microphone preamp is identical. Differences between either M2 version and competing interfaces are much larger.

Quick switching between line outputs revealed no audible difference. After longer listening, we slightly preferred the updated M2. Both are very successful products with suitable studio sound from TRS and RCA outputs: high detail, wide stereo and no audible tonal or other distortion. There are no DSP effects or mixer, the panel is basic and headphone volume is moderate. The focus is input/output sound, clearly better than a typical product at the same price.

Conclusions

The updated MOTU M2 did not disappoint. The American company handled the component shortage very well, finding an equally good alternative at the same price. Original-version owners have no reason to replace their interface: in practice, differences are negligible. New-version buyers can be confident that their product is at least as good, perhaps slightly better.

For extra dedicated line inputs, consider the MOTU M4. Its outputs and microphone inputs are identical, and even the PCB looks almost the same. Only the M4 adds an input/playback balance knob for direct monitoring, needed when recording voice or instruments with a backing track. If outputs are your main concern, the less expensive M2 is a safe choice.

For professional work needing exceptionally low latency, DSP effects or expandable channel counts, consider more expensive MOTU interfaces.

Note. This is an adapted machine translation into English. It follows the “In simple terms” approach. Read the original article at https://prosound.ixbt.com/interfaces/motu-m2-v2.shtml.