Shifted audio channels when the routing is set to Chain

[evgazloy]

Not sure if this is a bug or not. When the routing of a device, for example, Stereo Panner is set to the master mode everything is ok and sounds as it's supposed to.

And on E4L Master Bus I get these levels on the meter:

All 16 channels are used. Pay attention on the "pattern" of the levels.

But when the routing is set to the chain mode, only 14 channels are used and it sounds not as expected.

As you can see it looks like it starts from the 3rd channel and the first two channels are lost.

For fixing that I added +1 block in e4l.bus.send.maxpat:

Laptop: Apple M1 Pro OS: Mac OS Sonoma 14.0 (23A344) Live: 11.3.13 Max: 8.5.5

[mcslee]

Hrm, this is strange, I am not able to reproduce this on my system at the moment. How have you installed E4L? Did you checkout the GitHub repo directly or download a release ZIP file? Have you made any local modifications?

Can you share screenshots of the full Ableton mixer? Or share the whole live set project file in which this is occuring?

[mcslee]

Are there other devices on the chain in the track with the E4L Stereo Panner? I'm wondering if there are some other devices that may also have auxiliary inputs, e.g. assuming your track is called "Source Panner" can you show me what's in the dropdown if you try to route audio to this track from another?

[evgazloy]

I've found what is causing this issue - any 3rd party plugin with a sidechain input, such as a compressor, placed before Panner.

[evgazloy]

You are right:

[mcslee]

Okay - glad we've nailed down the source. The Live APIs for routing audio across tracks/devices are not based upon device objects, but rather they basically mimic what those routing UIs looks like. A routing target is specified via two parameters, each a list of options. (1) the "Track/Bus" options, (2) and then for each "Track/Bus" we get a secondary list of device inputs. The API provides the text labels of these destinations, but those are unreliable because the user may rename devices in Live - the text labels are the user-editable labels, not the canonical device name.

There is not a public API that I have found for "tell me which are the inputs of this particular device" - so I implemented that myself by iterating over the devices on the track, keeping a count of them and how many inputs they expose, and using this to determine where the routing inputs are for the next device in the chain.

This logic is all inside that e4l.bus.chain_index patch that you put the + 1 after. I just dug into that again, and into the further helper e4l.live.count_aux_inputs and lo and behold, it looks like I had left a comment about this very issue. This unfortunately suggests I have already gone to battle with it and could not find a general solution. If the Max 4 Live API doesn't tell us about VST sidechains, this may be very difficult to fix.

This is admittedly one of the uglier parts of the E4L implementation, all hacking around the fact that Ableton is really fundamentally dealing with stereo audio pairs.

An ugly workaround is to break your track chain in two. You can put your VST chain on one Ableton track, then route the output of that track to a second track which Monitors its input with the E4L devices there. This way the VST sidechain inputs won't interfere with E4L's routing code. It's not ideal, but it works.

It seems like you're comfortable enough with Max to have dug into the patch and figured out what's roughly going on... totally open to suggestions or ideas if you're able to figure out how to get any info out of the Live API that would make it clear when there are extra VST sidechain inputs present. I'll also try to take a look to see if anything has changed in what the Live API reports since I originally wrote this.

[mcslee]

Just documenting a bit of what I've found as I refresh myself on this. Looking at the LOM documentation: https://docs.cycling74.com/max8/vignettes/live_object_model

What I'm seeing here is that the PluginDevice object type (what you get when you query a VST) does not have the audio_inputs field that can be seen on the MaxDevice object type immediately below. Don't think we can get at that programatically. Would probably require looking at all the available inputs for the track and matching by VST name.

[evgazloy]

Yeah, I've seen that too. The basic workaround that came in my head was counting available routing channels. At first glance, it works even with multiple plugins with sidechain inputs.

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[evgazloy]

Needs further improvements, it's not working if a vst is placed after Panner.

[evgazloy]

Okay, I ended up matching device names as you suggested. Since we are dealing with names, we don't need to count the audio inputs of max devices anymore.

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[evgazloy]

Committed to the fork https://github.com/evgazloy/EnvelopForLive

[mcslee]

Hrm, I've grabbed your code here, but it doesn't seem to be working for me. I'm seeing a channel offset problem just routing one panner into a meter. Note that there's no signal in the first channel (the W level).

I think there are other pitfalls that this approach amy run into, since there is also no enforcement that device names are unique. For instance, two E4L Meter instances can be placed into the same chain (that's contrived, but you could imagine putting a Reverb between them, or some other device).

It might be possible to implement some kind of hybrid counting-approach, knowing that E4L devices have pairs from 3/4 up to 17/18. But this starts to feel very hacky/brittle to me. I really wish the Live API exposed inputs on PluginDevice objects, or offered some kind of real connection between routing_channels and devices beyond "the string in this dictionary is the same as the device name." Not holding my breath for this though.

There are also potentially weird cases when you start putting devices in racks... which can have multiple chains both with devices of the same name.