MOTU M6 Audio Interface Review

[welwynnick]

The original M4 design used an ESS ES9016S but subsequent revisions use an ESS ES9026pro (same as UL Mk5). I haven't seen a teardown of the M6, but I assume it also uses an ES9026pro as the manual has the same specs for the M4 and M6. I believe the M4 design only used 6 of 8 DAC channels (4 for line outputs, 2 in parallel for headphone out), so adding another headphone out wouldn't require a new DAC chip.
EDIT: Confirmed ES9026pro -> https://prosound.ixbt.com/interfaces/motu-m6.shtml.

Confirmed here as well:

I think the new version of the 16A uses the ESS ES9026pro as well, that's now caught up with the UL Mk5 on performance.
It's not state of the art, but I think that now qualifies it as "good enough" for a DAC.
It's interesting that professional audio interfaces, with no real need to be flavour of the month, seem to match the DAC chip manufacturers' claimed performance.

 

[Rja4000]

the input starts to saturate at around -10 dBFS

I have an old Motu 828 mk 3 Firewire that has the exact same behavior.

 

[SuicideSquid]

Any chance you can find a way to test those microphone preamps?

With an interface like this I expect most users will be going straight from a mic into the interface and not running through external preamps or other outboard gear that would use the TRS line ins.

 

[Steve Dallas]

Any chance you can find a way to test those microphone preamps?

With an interface like this I expect most users will be going straight from a mic into the interface and not running through external preamps or other outboard gear that would use the TRS line ins.

A sizable percentage of the guitar and bass community use modelers and other processors plugged into TRS line-ins. Probably a lot of piano / synth players do as well. Then there are Roland V Drums, etc.

 

[Cbdb2]

Ah! I missed this distinction. Will see if I can remeasure tonight.

Looks like the combo trs inputs are instrument inputs (1 or 2 Mohm and more gain) that can be used as line ins. That high input impedance and extra gain will drive up the noise.

 

[amirm]

Any chance you can find a way to test those microphone preamps

That's the same inputs I tested. Mic input just adds 6 dB more gain making saturation worse.

 

[SuicideSquid]

A sizable percentage of the guitar and bass community use modelers and other processors plugged into TRS line-ins. Probably a lot of piano / synth players do as well. Then there are Roland V Drums, etc.

I'm one of them. I do most of my guitar and bass recording that way. Can't record vocals or flute or acoustic guitar through TRS inputs though unless you have outboard preamps, and you're not usually buying a budget interface with built in preamps if you're planning to use outboards. Some people will use the TRS inputs - almost everyone will use the mic inputs.

That's the same inputs I tested. Mic input just adds 6 dB more gain making saturation worse.

Thank you for clarifying! I thought it was one of the two line-level inputs, didn't realize it was into the preamp inputs. That's very helpful.

 

[Jimster480]

Looks decent overall, I mean the performance of the DAC is nearly SOTA and I would argue the ADC is "good enough" for most situations?

 

[Postlan]

There’s a reason why the full potential of the ESS chip isn’t being realized, and ultimately, it means that something has gone wrong or been compromised in the design or in the manufacturing process.

 

[Pariah Zero]

Looks decent overall, I mean the performance of the DAC is nearly SOTA and I would argue the ADC is "good enough" for most situations?

ADC looks more or less on par with the Focusrite 2i2v3, and its siblings in MOTU's "M" series. The ADC also doesn't look as rough as the Focusrite 2i2v4. There's certainly more noise, but hovering around the limits of 16-bit is perfectly adequate.

Food for thought: When a Neumann U87ai has a self-noise of 12-14 dB, the Telefunken C12 has 16 db, it's not necessarily the audio interface that's the proverbial weakest link. And that's if you're going to spend a few grand on a mic. (There are more consumer-grade mics like the Rode NT1 whose self-noise is a "mere" 4.5 dB)

I'm not sure I caught/understood how the M6'd ADC SINAD graph shows ~93 dB: And yet the comparison graph shows ~100 dB? I figure @amirm may have posted the wrong graphic, or I need to read & watch the videos on how to interpret them again.

 

[amirm]

I'm not sure I caught/understood how the M6'd ADC SINAD graph shows ~93 dB: And yet the comparison graph shows ~100 dB? I figure @amirm may have posted the wrong graphic, or I need to read & watch the videos on how to interpret them again.

It gets to 100 dB if you drive it at -10 dBFS. I chose -3.5 dB for the dashboard that gave the 93 dB number. Other ADCs were tested at almost 0 dBFS so I tried to stay as close to that as possible to make comparisons fair.

 

[amirm]

Looks decent overall, I mean the performance of the DAC is nearly SOTA and I would argue the ADC is "good enough" for most situations?

The sharp increase in distortion at as you get to closer and closer to 0 dBFS is bothersome. For my youtube videos for example, I attempt to get as close to 0 dBFS without of course going over. Recording 10 dB lower to avoid distortion would mean softer playback for viewers/lower dynamic range.

The only limitation here needs to be 0 dBFS. Anything lower -- just like DAC testing -- should be optimal approaching 0 dBFS.

 

[Cbdb2]

The sharp increase in distortion at as you get to closer and closer to 0 dBFS is bothersome. For my youtube videos for example, I attempt to get as close to 0 dBFS without of course going over. Recording 10 dB lower to avoid distortion would mean softer playback for viewers/lower dynamic range.

The only limitation here needs to be 0 dBFS. Anything lower -- just like DAC testing -- should be optimal approaching 0 dBFS.

I wonder if the TRS ins (5,6) take a higher level than the combo inputs? The combo ins look like instrument inputs not line ins. Not really an excuse they call them line ins so they should be able to take line level. Ive owned an M4 for a couple of years now but have only used the combo inputs for mics. Thank you Amir for this info.

 

[Rja4000]

The sharp increase in distortion at as you get to closer and closer to 0 dBFS is bothersome. For my youtube videos for example, I attempt to get as close to 0 dBFS without of course going over. Recording 10 dB lower to avoid distortion would mean softer playback for viewers/lower dynamic range.

The only limitation here needs to be 0 dBFS. Anything lower -- just like DAC testing -- should be optimal approaching 0 dBFS.

For professional broadcasting (and, therefore, for professional equipment), there are standards specifying the target levels.

Most used were EBU R68 and SMPTE RP155.
They specify the target Alignment level (average level, somehow) for recording and broadcasting digital audio.
EBU R68 standardizes alignment level at -18dBFS and 0dBu (0dBFS is then 18dBu), while SMPTE gives -20dBFS and +4dBu as a target (0dBFS is at 24dBu).
Again, alignment level is somehow an average level, so peaks may be much higher, which is why it's specified with such a margin.

Note that EBU explains this level partly because they want to keep any "True peak" (so including any intersample over) below the digital 0dBFS.

A basic description of those standards may be found here: https://www.soundonsound.com/sound-advice/q-what-are-reference-levels-digital-audio-systems
You'll see that, in professional world, the analog section is supposed to start saturating way beyond the level where the ADC reaches digital saturation.

Non professional interfaces are often using an alignment level at -10dBV (0.3V), so 3V (around 12dBu) seems a reasonable 0dBFS target for those.

Nowadays, standards are more targetting to keep apparent loudness of a program at the same level, and are therefore using LUFS as reference.
See as an example EBU R128.
(https://tech.ebu.ch/docs/r/r128.pdf)

Of course, all this is meant to standardize the apparent level while always keeping the signal peaks free of distortion, so when testing equipment you'll want to use a continuous signal with level at or close to the maximum level (0dBFS).

 

[Steve Dallas]

Ah! I missed this distinction. Will see if I can remeasure tonight.

I think this needs to happen for the review to be complete.

 

[designfx]

I think the new version of the 16A uses the ESS ES9026pro as well, that's now caught up with the UL Mk5 on performance.

Makes sense, you're probably right, and MOTU also used the ESS ES9026pro in the latest version of the 828 (2024). So that would be consistent across product designs.

BTW, the MOTU 828 (2024) uses the AKM AK5572EN and AKM 5578EN for the ADC chips.

Would love to see ASR's take on the new 828, can't find a lot on it yet, but it seems like MOTU is really building on the UL Mk5 platform in a big way now. I suspect the 828 numbers will be close to the UL mk5 and new 16A.

FYI here's a review for the new 828 that mentions the chips:

Motu 828 5th Gen, Quality Above All - Review

www.audiofader.com

 

[dasdoing]

I fed the M6 a 4 volt signal and adjusted its gain to near 0 dBFS

you used the preamp to make it hotter in the analog domain? you wouldn't do that in a real world application since you would gain nothing. and doesn't that mean it was hotter than 14dBu when it hit the ADC? was the 18dBu sweep done with zero (pre-amp) gain?

 

[amirm]

Review cleaned up and new tests added for Line In 5&6. Much better performance as far as saturation is concerned.

 

[amirm]

you used the preamp to make it hotter in the analog domain? you wouldn't do that in a real world application since you would gain nothing. and doesn't that mean it was hotter than 14dBu when it hit the ADC? was the 18dBu sweep done with zero (pre-amp) gain?

The Trim control was barely above its minimum. Same issue exists with setting the trim to minimum and increasing input level to what the spec calls for.

 

[Steve Dallas]

Review cleaned up and new tests added for Line In 5&6. Much better performance as far as saturation is concerned.

Thank you, Sir. You are a gentleman and a scholar!