For best results the following is true:
The Yamaha Steinberg USB Driver is required to connect MODX to your computer.

When using MODX even if the USB Audio Driver is not installed, a class compliant driver (OS standard driver) is automatically applied when the product is connected to the computer with a USB cable via the “TO HOST” port.

In some cases, depending on conditions or the specification of the host (computer/tablet), a drop-out noise in a recorded audio file can be produced as a result of an interruption in the signal flow. Usually setting the buffer size to a higher value can eliminate the problem however, if you encounter this issue when using the class compliant driver, and setting the buffer size to a higher value does not resolve the problem, please switch to the Yamaha Steinberg USB (YSUSB) Driver, if possible.

It is recommended that you to use the YSUSB driver when you want to try buffer size setting lower than a class compliant driver.

Clearly one would not want the audio coming into the MODX USB via Class Compliant operation to go right back out the USB.

There is a difference between the MainL/R Out (analog) and the USB MainL/R (digital).

Audio returning from the Class Compliant host device to MODX is typically sent to the analog MainL/R, so you can hear it.
If you return audio from a host device to the DigitalL/R it arrives in the MODX internal mixer on its own audio channel. You can then route it to any of the MODX available outputs using the “Digital In” parameter set within each Performance.

if the thumb drive connector has Class Compliant Audio let me know

If you are referring to the MODX’s TO DEVICE port, it is capable of writing stereo .wav (24-bit/44.1kHz) file to a connected USB stick.

In general, you should use the Yamaha Steinberg USB Driver whenever possible. Your questions are strangely written, what are you trying to do? If you are running a device that cannot run the preferred driver and you must use the class compliant (available) driver (as with an iPad or iPhone) then which of the MODX return ports are available will depend on the application you are running in the host, afaik.

OK, thanks for your help.
I am interested is working in Ubuntu Studio and with other Linux based devices, like this one here:

Daisy

It would be a lot more useful to access the USB MainL/R (digital) but I was asking because I am afraid this is only possible with the YSUSB driver, which is not Linux compatible.

With the Daisy it would be theoretically possible to externally process audio and return it to within the MODX over USB.
The Daisy can be controlled by MIDI also, so this would be like implanting an additional VAR within the MODX architecture.
The main benefit is that you could program the Daisy to be any type of processor, including types that have never been done before.
It can be done, but it involves cooking up a USB driver for Daisy that would enable access to all the audio channels (difficulty = unknown).
Daisy has analog audio in and out too, but since the MODX has no individual analog audio outputs this has limited usefulness.

What would be really cool is if the MODX to HOST would also power Daisy, but it will not.

Yes it's all Beanycopter stuff.

Yes it's all Beanycopter stuff.

Yes, it is... 🙂

Make sure you run through the traps of the class compliant driver. I thought there were more than 2 channels available to this driver. I'm not so sure that the class compliant driver doesn't give you access to the digital USB L&R channels. Using Montage (that's what I have) - I thought I was able to force Windows to use more than just 2 channels when no Yamaha/Steinberg driver was loaded.

That sounds promising. The Daisy has been covid delayed anyway. What are "the traps" you speak of?

Is anyone on this forum using their MODX USB audio connection with Ubuntu Studio or the Harrison Mixbus DAW?

I just mean make sure the class compliant driver isn't as limited as having 2 channels (Main L&R only). Running through the traps isn't trying to imply there's a menacing trap waiting to be discovered - but just to apply due diligence to ensure class compliant isn't as limited as stated.

I'm trying to find my old notes but can't find them - but seem to recall noticing more channels first when using Voicemeeter, noticing the number of channels supported - and initially thinking I was running with the Yamaha Steinburg drivers - but later finding out I had not yet installed the drivers on a new machine and was observing new features I had previously thought were not available to Windows class-compliant. I think I did track down a windows setting that "opens up" more channels. Somewhere I had a screenshot of this -

Found it: I think the discussion is around here:

https://yamahasynth.com/ask-a-question/use-montage-cubase-to-record-from-internet?start=20#reply-31034

Screenshots shown how to change the windows settings to show more audio channels using the class compliant driver. I'm just going by memory - but I'm pretty sure all of this work I had shown here was using class compliant (which I didn't initially think was the case when I authored the messages).

You may not want to use Windows - but if Windows class compliant has more than just Main L&R - my thought is that Linux or other operating systems would have the same provisions.

Not exactly the same system you're playing with but I have connected the MODX to a Raspberry PI, which is running a form of Ubuntu. Using Linux versions of Reaper or Audacity DAW programs I get two channels of USB audio into the Pi and can route audio out through USB back to the MODX or through ALSA, the Pi's default audio mixer, to other supported audio outputs. I only tried a quick test to see if the MODX would work at all with the Raspberry Pi so can' t tell you much more. Good luck with your project.

Thanks Kevin - this is great information for me.

Which Raspberry Pi do you use?
I have one 3B+ and two 0W for various projects.
I might try the 0W just on a lark. I will need to get a bluetooth keyboard as the only
USB port is taken up with the wireless dongle for a Logitech 200 keyboard.

Are you using the Raspbian latest OS version (Buster they call it) or something else?

I also have a pair of Odroid U3+ running "Lubuntu 14.04" as it's called.
These are more powerful and flexible but basically quite similar.
I'll have to give them a try and see how they run, I hadn't thought of that until I read your post.

thanks again -

I'm using the Pi 3B+ running the Buster version of Pi OS. I'm using an old Logitech keyboard as well so the dongle takes up one of the USB ports. MODX audio over USB seems to work well but I haven't tried MIDI yet. I'm not thinking of using the Pi for serious audio work but it's fun to see how far I can push it!

Yes, that is my approach as well. I want to push this and see what happens.

I tried downloading the Mixbus for Linux but alas it is for x86 processor only.

So then I found a load of Ubuntu Studio for my Odroid U3+ which is more
powerful than the RPi 3B+. It also has a microphone input built-in on the
headset jack (the RPi has audio out and video out on the same jack, no
audio in is built-in on any of the RPi - you have to add some hardware).
I have this little iMM-6 calibrated microphone which I can plug in there.

The Odroid has an SD card but also has an eMMC memory module which
is faster than a SD card. I tried to put the OS into that but ran into a problem.
There are several different eMMC standards so the OS you load has to have
the correct eMMC driver and this Ubuntu Studio has the wrong one. So I can
put it in a SD card and then will try to connect MODX to the DAW in Ubuntu
Studio and see what happens. I never seem to have enough SD cards no
matter how many I buy! I have some 128 Gb but that is too large for the U3+
Odroid that I have (a discontinued device I was using for something else up
until recently). So I am off to Fry's again...

I got Ubuntu Studio working on the Odroid U3+ using a SD card. I got the built-in headset jack working but
I can't control the mic level. In Audacity the 'mic gain slider' won't move and the bubble says "unavailable".
I tried all the mixers (alsamixer both GUI and command line, jack, pulse, etc.) but the iMM-6 mic is too loud.
The output is good coming out both the headset jack and to the monitor through the HDMI. I tried using
the MODX USB and it was the opposite of Kevin's Raspberry - I couldn't get the audio working so far but
in Ardour ALSA/JACK does see all 3 MIDI bus working and that's impressive with the compliant driver.

more to come!

Updated my MODX and in looking in the readme:
*********************************************************
Fixes and Enhancements

New features;
- New Performances have been added.
- The Smart Morph function has been added.
- New functions have been added to the Pattern Sequencer.
- The DAW Remote function has been added.
- Controllability and playability have been improved.

New features;
- New effect types have been added.
- New Performances have been added.
- The Pattern Sequencer function has been added.
- You can now play songs, patterns and audio files from the Live Set display. < - - this is news to me!
- Super Knob Link has been added to the data that is recorded in the Scene function.
- Keyboard Control has been added to the data that is recorded in the Scene function.
- Increased the range of the LFO Speed parameter.
- You can now connect MIDI equipment via the USB TO DEVICE terminal. < - - I was asking about this earlier in this thread

About my little Daisy, which came in the mail yesterday. If the MIDI is available on the USB TO DEVICE (that's where you put the USB flash drive)
then it would be possible to plug in the Daisy to both power the little guy AND to send MIDI from Daisy to the MODX. That might be really cool.

The next question would be can you send MIDI from MODX to USB TO DEVICE? Nothing about that in the Quick Setup display.

And finally would there be any AUDIO USB path to/from the USB TO DEVICE? (...seems unlikely)

You cannot send anything TO the USB TO DEVICE connected audio device.

Only MIDI can be used (not audio).

Direction flow goes FROM the device (MIDI) TO the keyboard.

From there, MIDI channel and MIDI mode rules apply.

Yes, I expected as much, but hope reigns eternal.

Now that other question I had, about how you are able to play audio files from the Live Set display.
- You can now play songs, patterns and audio files from the Live Set display. < - - this is news to me!

I don't see a way to do it. Any tips?

I found the MIC level in the Ubuntu initialization routine so maybe hope I can get that working.
And the two guys who cooked up the Ubuntu Studio 14.04 for my Odroid have now gotten some
success with cooking up an 18.04 image. It sounds much improved so I am looking forward to
getting the MODX USB audio working with this new OS. Now that the MODX 2.5 is out I expect
the DAW control on MIDI bus 2 to be working since ALSA does see all three USB MIDI from MODX.

Good times!