MOTU M6: USB audio interface with 4 microphone inputs

The MOTU M6 builds on the success of the American company's most affordable M-series USB interfaces. The smaller M2 and M4 remain bestsellers, but their channel counts cannot be expanded. Users needing to record more than two channels previously had to consider expensive advanced models. The six-channel M6 fills this gap with four independent microphone inputs and two line inputs.

M6 electronics and features largely match the smaller models. It uses the same excellent preamps, ADCs and DACs proven in the M2 and M4. Specified round-trip latency remains 2.5 ms with a 32-sample buffer at 96 kHz. USB bus power is still possible, but only from a modern port supplying enough current. Otherwise, use the included small 15 W power adapter.

The MOTU M6 is more than an M2/M4 with extra inputs. First, RCA sockets are gone, suggesting a strictly professional focus. Second, a new A/B button switches between two monitor pairs. Third, two independent headphone outputs can carry different backing tracks: one from channels 1/2 and the other from 3/4.

These apparently small details can make daily work easier and justify choosing the MOTU M6. The manufacturer also offers more professional compact interfaces, the MOTU Ultralite MK5 and MOTU 624, with a hardware mixer and effects processor. The M series prioritizes affordability and high sound quality over maximum onboard functions. Still, MOTU has given the M6 a few more features.

The M6 case is larger than the M2/M4 and even the higher-end Ultralite and 624. MOTU could have made it more compact but left several extra centimetres at the sides. This preference for larger dimensions helps everyday use. Rear connections are easier to reach, and there is more finger space around the knobs, reducing accidental changes to adjacent channels. As before, all knobs are digital, with 1 dB steps, keeping left and right channels matched. They turn with light, pleasant resistance and have no looseness.

MOTU build quality remains excellent: a strong all-metal powder-coated case and high-quality Amphenol sockets. Recent revisions no longer carry Made in USA or Assembled in USA labels, but component and sound quality are unaffected, as our separate investigation showed. Read our articles Comparing the original and current versions of the MOTU M2 USB audio interface, and Comparing the original and current versions of the MOTU M4 USB audio interface.

MOTU M6 specifications

Full specifications are currently available only in the updated manual covering the M2/M4/M6 range. They are identical across the models, so choose according to the functions you actually need.

The manufacturer summarizes I/O specifications and signal levels in a separate table.

As expected, internal electronics match the smaller models.

Inside is a 32-bit Cortex-M7 ATSAMS70N20 ARM processor, as in the other M-series models.

One 8-channel ES9026PRO DAC serves all 4 analogue output channels. Its specifications are 124 dBA dynamic range and -110 dB THD+N.

Two ADC chips cover the 6 recording channels: a 2-channel ESS ES9820Q and a 4-channel ESS ES9840Q. Both specify 116 dBA dynamic range and -108 dB THD+N.

As in the other models, the low-noise integrated preamp is a digitally controlled THAT 6263.

Each headphone output has its own OPA1688A integrated amplifier, delivering 3.3 V RMS with low distortion.

We tested the M6 with firmware 2.01 from November 2022. The panel now shows an M6 image alongside the M2 and M4. The driver is universal across the family. There is no panel with software controls: all adjustments use the M6 hardware knobs and buttons.

In foobar 2000 using ASIO, the small sample-rate switching issue remains. A file must be restarted before the rate changes. This affects every model in the range and may be a driver characteristic.

With the lowest latency option, round-trip latency is just 6 ms at a 64-sample buffer and 44.1 kHz.

MOTU advertises 2.5 ms latency with a 64-sample buffer at 96 kHz.

Our measurements confirm the claim. However, a very small 32-sample buffer greatly increases the risk of crackling from buffer underruns. For USB devices, realistic latency settings of 4–8 ms give audio applications better stability.

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

ASIO diagnostics

Despite the 6 in the M6 name, it has only 4 output channels, like the MOTU M4. Inputs include 6 physical and 4 virtual channels. Loopback and Loopback Mix channels broadcast signals from all inputs and outputs together over the internet.

RMAA PRO measurements

We measured with TRS outputs connected to interface inputs.

MOTU M6 measurements at 24-bit/44 kHz are on a separate page.

The 3 dB difference between input and output levels prevented record dynamic range in the loopback test. More importantly, the noise spectrum is very even and free of interference, despite USB bus power.

Distortion is an excellent 0.00016%, matching top-level products. The harmonic spectrum is also favourable.

The M6 can run entirely from a modern USB-C port, or from any USB port, even an old one, when using the included 15 W adapter. We found no sound-quality difference between power methods.

Meters show input and output levels independently of the level knobs. They display digital signal levels and indicate data reaching the inputs or outputs. M-series interfaces have no processing, low-cut filters or EQ. All later processing is intended to take place in a DAW. Light versions of MOTU Performer and Ableton Live are included, together with sounds and effects.

We recorded voice through a Neumann TLM103 into the MOTU M6 and compared it with a separate, more expensive preamp and ADC. As expected, the M6 delivered excellent results: natural tone, high detail and no audible coloration. Recording quality is a very good example of what a compact USB-powered device can achieve.

Line output quality is also high. We connected ADAM active monitors and a separate balanced amplifier with passive speakers. Performance meets a high professional standard, suitable for demanding work or simply enjoyable music listening. The headphone output is not the M series' strongest feature, but it is better than many in this class. There is certainly enough volume for common headphone models.

Conclusions

The MOTU M6 fits naturally into the M series, offering 4 microphone and 2 true line inputs with the quality familiar from the M2 and M4. Using the same electronics made testing less exciting, but MOTU has preserved the strengths and added useful functions. These include an extra headphone output assignable to channels 3/4 and monitor-controller functions for quick switching between monitor pairs.

Users who do not need these additions can choose the smaller MOTU M2 or M4. For professional studio work requiring extremely low latency, DSP effects or expandable channel counts, consider the more expensive MOTU Ultralite and MOTU 624.

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-m6.shtml.