Why is only one USB audio path allowed?

[The Elf]

I can only speak for myself and Cubase, but switching ASIO drivers is a load of hassle.

[Drew Stephenson]

It's pretty straightforward on Reaper; plug in your two interfaces, go to the options list and select the one you want and confirm the number of inputs and outputs.
Never had any glitches off the back of it.

[ef37a]

You can use multiple audio sources in Windows (W7 anyway) I did it some years ago but you have to use mme drivers and the tracks are not sync'ed. They don't even start recording together, quite. I was using Samplitude SE8 and that makes it very easy to slide tracks to sample accuracy. They don't of course STAY together but over a 3 minute song, close enough.

Hmm? Switching USB interfaces is easy enough in Sam I think? Won't be a one button hack though. I shall rig my M4 and the KA6 later and have a do! Mind you, both those interfaces have very solid, well behaved drivers.

Dave.

[Johnsy]

To get some idea of what's involved in syncing interfaces in the absence of a common clock, take a look at this:

https://www.youtube.com/watch?v=8jHLusUVa2Y

[The Elf]

It's pretty straightforward on Reaper; plug in your two interfaces, go to the options list and select the one you want and confirm the number of inputs and outputs.

I don't even have to do that in Cubase - it sorts all that out itself, but... Cubase loses all of my External Instrument/FX assignments, and I have to re-allocate all of the Control Room I/O. It's not an experience I want to repeat.

I once did it to record a TR-8S's separate outputs over USB - never, ever again. I could have recorded separate passes in far less time.

[Drew Stephenson]

It's pretty straightforward on Reaper; plug in your two interfaces, go to the options list and select the one you want and confirm the number of inputs and outputs.

I don't even have to do that in Cubase - it sorts all that out itself, but... Cubase loses all of my External Instrument/FX assignments, and I have to re-allocate all of the Control Room I/O. It's not an experience I want to repeat.

I once did it to record a TR-8S's separate outputs over USB - never, ever again. I could have recorded separate passes in far less time.

I think, given the options, I'd prefer Reaper's manual switching!

[The Elf]

With Reaper I don't create external links to hardware, so it's a non-issue, but then I don't have the same level of flexibility and speed (e.g. 'Render In Place' for hardware synths).

(Hint: 96 inputs and outputs!)

[merlyn]

The OP could try Voicemeeter Potato :

https://vb-audio.com/Voicemeeter/potato.htm

Potato is working along the lines of the video Johnsy posted above. (Good video BTW).

... I believe Apple handles multiple AI because devices are USB class compliant and dont need drivers.

Windows can handle multiple drivers if they are different but it cant handle multiple asio driver instances.

All devices need a driver. Mice, keyboards, graphics, even if the driver doesn't have to be installed. There's still a driver, it just came with the OS.

Class compliant devices have a driver -- all devices of that class e.g. USB audio use the same driver.

A key concept with Windows is 'third party'. To be of any use Windows needs third party software, third party drivers ... ASIO is a third party sound stack. Back in the day Steinberg decided that what was built into Windows wasn't up to snuff, and re-wrote it from scratch.

[Guest]

Aggregate devices on a Mac work will all audio interfaces, they do not have to be class compliant.

The best solution is to actually use a hardware clock connection between the devices and then you don't need to turn drift (resample) on at all. This all works perfectly.

I use drift (resample) occasionally for testing and as long as the clocks are not too far out of kilter it seems to handle it well, I'm not sure I would rely on it in a professional setting though. Lots of I/O and a few patchbays seems a better choice.

[MarkOne]

I understand that those clever boys and girls in Redmond did solve this for windows in the form of Direct X

But by the time they did ASIO ruled the world, and it’s much easier to develop your own driver for your own device and only test that combination, rather than the hassle of having to dig into a system level feature you don’t control.