[pottering]

"Yes this is what's happening in Ableton"

Are you sure? Because since your theory is based on grouping tracks, it is easy to test, by simply grouping all tracks in a Set with 20 or so tracks that use a decent chunk of CPU. Then all their CPU should shift from several cores into one single core/thread (according to your theory). Of course, being easy I already tested this with a Set that used Live's native devices (no CPU usage change), but I can't test with VSTs right now (none installed). Maybe VST hosting has that problem, but processing of audio summing, Live's own devices and M4L doesn't have any major problem with multi-core.

[varispeed]

Yes I did such tests and then compared the same scenario with jBridge.

[pottering]

I think you may be misreading that FAQ page, it mentions sidechain as the reason for using one thread for "dependant" tracks.

Sidechain is not mere grouping/routing like the chain PaulDavis described with ASCII art (different from Sends too), with sidechain the plugin needs the audio from the other track for actual DSP processing, that's why sidechained tracks become a single thread "dependant" signal flow.

That page also mentions Live can use one thread per Chain if needed (for non Live-users, Chains are internal routings inside one single track), so it clearly states Live can use more than one core for one single Track.

Also, plugins like u-HE's use multicore just fine for a single instance, if you disable their own multicore handling (which conflicts with Live's multicore handling).

For Live's own devices, I'm pretty sure multicore works just fine, just tested again with Groups and Sends.

Don't know what problem you have, but it is not simply Live's multicore handling, it is some specific scenario you hit upon.

[varispeed]

It doesn't do that. Whatever seems dependant gets lumped into one thread and limited to a single core. Fortunately Ableton cannot limit what plugins do in their own runtime so as you say U-HE multicore functionality works just fine and jBridge can run plugins off of separate processes. Not sure why people are being defensive about it or attack for pointing this flaw out. It's great that you think Ableton works as intended for you, but once you go beyond Live devices and use more professional tools, you'll hit the wall. People who I know hit this as well just moved to Reaper, but I cannot get on with its workflow.