Motu 624 Audio Interface Review

[BDWoody]

That's a fair point...
But how many here are also playing music and recording home?

I don't say we should start reviewing true pro devices (as for any pro tools, there are other factors than raw sound quality involved. Reliability, pro-world acceptance and integration come to mind), but testing this kind of amateur or semi-pro interface, including mic input, make sense to me.
A subset of tests (SINAD vs gain?) is probably enough to assess mic input quality, on top of the standard.

And there is enough of a market for those to lead to serious impact on price/quality, also for lambda consumer.
See the number of decent performing interfaces for a low price. Aren't they better options than Audiophooley DACs ?

Thats what got me looking into them. Specifically, the ability to offer both digital and analog out would make it a lot easier for me to utilize more of the amps and speakers and DAC's around the place in a home theater situation. Relatively speaking, these aren't that expensive...

 

[Thomas savage]

No panther , how am I ment to know how good this thing is ...

 

[Rja4000]

I have 2 questions about measurements:

1. For ADC, what actually means the JTest ?
I guess I understand it for DAC, but what does it mean for an ADC ?

2. For THD+N vs Frequency, we often see bad performance due to high frequency noise, that we couldn't hear anyway
Isn't that more relevant to focus on THD (without N) only ?

 

[Blumlein 88]

@Rja4000 regarding microphone inputs. I use a 150 ohm metal film resistor to get a handle on EIN and basic noise floor. In terms of other factors I feed a -60 db signal from a good DAC (in my case March Audio DAC). With FFT gain you can at least see if distortion is reasonable or not. It wouldn't pass muster for a test lab showing full capability of the mic inputs. I could perhaps build a attentuator to do even better by attentuating the larger input from the DAC.

Now good pres will have an EIN spec near -130 db. But this is with 60 db of gain. Meaning you'd only actually have 70 db of dynamic range left (130 db EIN -60 db gain). Most good mic pre's claim around or a bit over 100 db SNR. Anytime you are using more than 30 db gain (which is almost always with a dynamic or ribbon mic) the mic pre isn't the limit on available dynamic range or SNR. Low level microphone preamps are actually pretty simple circuits anyway.

 

[audimus]

I think the proper context is missing here to evaluate the results.

First, the use of the word Pro. It could mean professional musicians or professional studios. Portable units like these are aimed at the lower end of both - garage bands or local bands using it for performances over a PA setup or a home studio to produce demo tapes or self-produced packages to sell or monetize over the Internet at a small scale. CD quality (or less in PA systems) is the typical target so the demands on fidelity in reality can be far less than the higher end of the audiophile market. So, expecting better theoretical performance for a “pro” product than a consumer audiophile quality is missing the context.

Second, the kind of inputs and its use. Primarily, mic inputs (which is important for most intended uses), line level inputs to plug instruments in, usb/thunderbolt/firewire interfaces (which are replacing midi interfaces of the past) to bring in a computing device for backup tracks, effects processing, recording, etc. The ADC measurements are most important for mic inputs and instrument line inputs which are typically low voltage sources if direct. The DAC for the digital inputs where the sampling rates, etc., are controlled at the source device and don’t vary a lot once set up.

While the measurements here give some useful information, they miss the mark somewhat in giving the full picture for its intended use and how it meets its targets. The performance of this unit far exceeds the requirements of this use and like amps playing up power numbers that don’t make a difference in practice, these companies play up the sampling rate numbers to say they are better.

There is a niche off-label use of these as pre-amp for headphones or amps for consumer audio, even multi-channel HT. Typically from tech savvy hobbyists as these things require more setup and configuration than most consumer gear. The sources are typically digital, may vary a lot in sampling rates. It doesn’t make sense to use these as a stereo headphone amp for phono or other analog sources as there are far cheaper great units for those. So, even for the justifiable off label use, the DAC performance (and the voltage and impedance characteristics) is the most important relative to what is typically connected at the input and output ends rather than the ADC. The unit seems to do very well relative to most consumer audio for that niche especially if more than stereo is needed. Seems like it far exceeds most of the miniDSP DACs.

I am interested in these units as a combined multi-channel HT set up as well as for garage band gigs and practice and asked a question earlier on the experiences for the former with the Motu 8A. Not much experience there at least in this crowd.

 

[audimus]

Another important characteristic of the target use of these things different from typical consumer audio reproduction is multiple parallel source inputs in use (analog and digital). Similar to cross-talk channels in consumer repro use, the handling of multiple source inputs without any interference or negative effects from each other (including latency in each path) is also critical to evaluate with or without mixing. Of course, the tests here aren’t designed to capture those metrics given its focus on consumer audio reproduction goals.

 

[DonH56]

Ask over on the EM (Electronic Musician) or similar sites. Again, this site targets mostly audio/video enthusiasts IMO, not the home-recording folk. While I'd love to see @amirm take reviews of these units to the next level, I do not feel this is really the appropriate venue, and would take a lot more of his time to satisfy a niche of the niche...

IMO! - Don

 

[audimus]

Sure. My earlier post was asking about the use of a device like this for consumer home audio multi-channel use not as band equipment.

Just setting the measurements in the context of its intended and off label use so that the measurements are interpreted in that context. No need to get defensive.

 

[Rja4000]

Ask over on the EM (Electronic Musician) or similar sites. Again, this site targets mostly audio/video enthusiasts IMO, not the home-recording folk. While I'd love to see @amirm take reviews of these units to the next level, I do not feel this is really the appropriate venue, and would take a lot more of his time to satisfy a niche of the niche...

IMO! - Don

I'm not sure if this market is actually much smaller than the one of audio enthusiast, especially amongst people potentially reading this site.
But I get your point and I agree.
Let Amir focus more on speaker amps, as an example, which is probably where the most is still to be uncovered.

 

[Rja4000]

I could perhaps build a attentuator to do even better by attentuating the larger input from the DAC.

Now good pres will have an EIN spec near -130 db. But this is with 60 db of gain. Meaning you'd only actually have 70 db of dynamic range left (130 db EIN -60 db gain).

Yes, that's basically what I do: use the DI as an attenuator (and impedance adapter).
And I end up with this kind of figure.

 

[amirm]

1. For ADC, what actually means the JTest ?
I guess I understand it for DAC, but what does it mean for an ADC ?

It doesn't have the same meaning as in DAC tests if that is what you are asking. It is just a convenient high-frequency tone that can be generated by my analyzer without the need for dither, etc.

 

[amirm]

2. For THD+N vs Frequency, we often see bad performance due to high frequency noise, that we couldn't hear anyway
Isn't that more relevant to focus on THD (without N) only ?

That wouldn't fix the issue you are mentioning as high-frequency "noise" is not the problem. That only derates the measurements by a few dB. What makes it much worse is correlated, tall spikes in ultrasonics which could be images due to lack of good reconstruction filter, outright harmonics or something spurious. These knock down measurements often by tens of dBs.

I also have to see if there is a way to plot what you are asking. The FFT measurements without noise are one-shot requiring manual plotting to get a graph. I will look....

 

[LTig]

1. For ADC, what actually means the JTest ?
I guess I understand it for DAC, but what does it mean for an ADC ?

It doesn't have the same meaning as in DAC tests if that is what you are asking. It is just a convenient high-frequency tone that can be generated by my analyzer without the need for dither, etc.

How I understand it one could use a sinus as input to the ADC and check the FFT for width of the peak and any spurious signals. Not sure if all spurious signals can be called jitter, but those which are sidebands of the main peak should qualify, as a broad foot of the peak would do.

 

[audimus]

I have a Motu 828ES (Used to have Lynx Hilo/Prism Orpheus/Antelope gear among others) and that's why I don't send in my Motu 828ES. I use it 8-12 hours a day. I will admit the drivers have been awesome for me without fail and the routing options are awesome.

You can use Voicemeeter Potato and use the Motu as a 5.1 or 7.1 surround out from your computer for blu-rays.

Thanks. This was the kind of hands-on information I was looking for. Voicemeeter is not required to use it as a multi-channel play device, no? Does Motu provide ASIO drivers or do you use ASIO4all?

The drivers should make it available as a multi-channel device for any source to play straight to it as 5.1 or 7.1 LPCM via USB. It can be used in exclusive mode by a source to bypass window processing.

Unless you have some other requirements to route sources to different end points. I use Voicemeeter Banana to route to different outputs from PC depending on whether it is music or HT.

Regarding Netflix, you cannot get multi-channel LPCM digital out extracted without using a HDCP compliant DAC/processor. You can use HDCP compliant sound cards (including onboard audio) that can output analog or compressed S/PDIF digital limited to 5.1 to send it to a non HDCP compliant unit like the Motu. You can output lossless digital via HDMI only if the unit it is connected to is also HDCP compliant. There are some HDCP cheating devices out there to do lossless digital extraction which are in the gray area if not illegal. Voicemeeter cannot be in that path except via some external loopback after extraction.

 

[amirm]

Does Motu provide ASIO drivers or do you use ASIO4all?

Every pro interface supports ASIO. ASIO was created for their industry. I noted that is what I used in my review.

I would not at all base any commercial work on ASIO4ALL operating. It simply is no reliable enough for that use.

 

[audimus]

There are a large number of moving part on a PC especially for using Pro equipment. I can see why Voicemeeter made it simpler because it handles both ASIO and Window device configurations well.

Problem is the software that comes with Pro equipment have target use for a DAW application to talk directly to the gear where conceptually there are N number of channels (not L, R, C, etc) and via ASIO. DAW applications ignore any of the Windows configurations and provide their own UI to configure them.

Consumer player software on the other hand typically rely on the Windows device configuration and just use the direct mode at best to those devices, not necessarily direct ASIO. Voicemeeter and software like JRiver can bridge the two. Or the driver software provided by the Pro gear manufacturer can provide both ASIO access as well as set up a playback device in Windows Audio that can be configured as Stereo, Surround, etc with speaker channels mapped to the audio channels available on the device. This is the frustrating part of off-label uses.

Don’t know if Motu software does this configuration. I can’t find anything in the Motu manuals that talks about this because that is not their target use.

If you go Control Panel->Hardware and Sound->Manage audio devices, you should see the Motu installed device under Playback. If you select it, and the configure button at bottom left remains greyed out, then it can only do Stereo because that is the way Motu drivers are set up under Windows Audio. If configure is enabled, and you click it, it will allow you to select speaker configuration. If it only lists Mono and Stereo, then again Motu driver is limited. But if it lists surround modes (like it does for the Voicemeeter installed devices) then you select the surround configuration you want and then the consumer player software will send surround out when that device is selected as default or in the player interface. What I don’t know is whether Motu does this for its Windows device driver or just forces stereo.

 

[amirm]

Ideally, you want to simulate a 1mV 50 ohm microphone, with enough gain to reach near 0dBFS, and see what happens, in terms of noise, distortion, bandwidth, frequency response, linearity, max level, max and min gain.

Here is the starter with 1mv/40 ohm input with Motu:

For kicks, I also ran the same test on Behringer UMC204HD:

As noted, this is with max gain. It is not able to reach 0 dBFS.

The same two spikes exist in there too so this must be noise in the APx555 analog generator.

1 millivolt seems awfully small signal here. Why not standardize on something higher?

 

[Rja4000]

. What I don’t know is whether Motu does this for its Windows device driver or just forces stereo.

I don't know exactly what you want to achieve, but if that's to have video sound, why not to use one dedicated video interface, like Motu HDX-SDI Thunderbold or similar?
Why to reinvent the wheel?
Or am I missing something?

 

[audimus]

Passive microphone outputs are in the 1-2mV range. Condenser microphones with active circuitry can do more with phantom power enabled.

The above values are at the lower end. The workhorse Shure SM58 generates around 1.85 mV at 150 ohms rated.

 

[audimus]

I don't know exactly what you want to achieve, but if that's to have video sound, why not to use one dedicated video interface, like Motu HDX-SDI Thunderbold or similar?
Why to reinvent the wheel?
Or am I missing something?

It is to use Motu as an external DAC for multi-channel sound out of the PC whether from a multi-channel SACD or a video player playing video with surround sound. Don’t need the Motu to do any video processing.