STM Mixer Stereo vs Mono

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Music Manic
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STM Mixer Stereo vs Mono

Post by Music Manic »

OK I'm a little confused. I think I may have asked this before but how does the Stereo channel behave relative to audio?

I sent a sine wave to both the Left and Right of the stereo channel and I phased one side expecting it to cancel out and it didn't? I the did it with 2 Mono channels and it cancelled out as expected.

Could someone explain the architecture of the stereo and mono channels, with regards to incoming audio and their phase options.

Thanks
fra77x2
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Re: STM Mixer Stereo vs Mono

Post by fra77x2 »

have you tried manual assignent?
Music Manic
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Re: STM Mixer Stereo vs Mono

Post by Music Manic »

fra77x2 wrote: Tue Nov 01, 2022 2:12 pm have you tried manual assignent?
I didn’t think DSP assignment would affect a single channel’s phase fra77x2. I will try it though

Do you know how to lock devices using the SDK so that they will be locked when I use them? I’d appreciate it.
fra77x2
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Re: STM Mixer Stereo vs Mono

Post by fra77x2 »

if you assign a dsp id on the module attributes and save the device it should work.

if a device is protected from editing in the sdk though the module attributes shouldn't be accessible. If I remember well
in this case perhaps you can fold a device and assign the dsp for the container module.

I suppose you use the PCI boards I thought scope 7 allows custom dsp assignment for both Xite and the pci boards with the normal scope software but i m not sure.
Music Manic
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Re: STM Mixer Stereo vs Mono

Post by Music Manic »

fra77x2 wrote: Tue Nov 01, 2022 5:00 pm if you assign a dsp id on the module attributes and save the device it should work.

if a device is protected from editing in the sdk though the module attributes shouldn't be accessible. If I remember well
in this case perhaps you can fold a device and assign the dsp for the container module.

I suppose you use the PCI boards I thought scope 7 allows custom dsp assignment for both Xite and the pci boards with the normal scope software but i m not sure.
Yes I’m running on PCI but I don’t think it’s a phase problem, maybe I’m not getting the architecture of the stereo channel

If you feed a stereo channel with a sine wave, the signs should cancel if one side is phase inverted. It doesn’t seem to happen in the STM mixer

Thanks for your help.
fra77x2
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Re: STM Mixer Stereo vs Mono

Post by fra77x2 »

In the sdk it is also possible to assign the dsp for the outer project window so anything that is dropped inside inherits this dsp. of course you can override other devices or packs of devices by assigning a different dsp to these. in the xite i use dsp 10 for asio and the mixer. This allows to route and mix as many asio channels without consuming sat communication. All effects loaded on dsp 10 are sample accurate. dsp 10 as the rest of the new dsps allow around 6500 cycles. These are plenty for a lot of effects. i get 4 samples latency from asio out to asio in that i compensate in the record preferences at reaper. this way the recorded file is sample accurate with the file in the daw.

I use other dsps for packs of monophonic synths or different polyphonic synths with 10-16 voices calculated each to be able to to fit in a dsp

It is a fantastic system for the modular lover and the experementalist. kinda difficult to use but this is my thing
fra77x2
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Re: STM Mixer Stereo vs Mono

Post by fra77x2 »

if the sines do not cancel but get lower in volume the perhaps it is the pan law or something.
if you load saw waves and you check a fft and you observe comb filtering then it is the phase
Music Manic
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Re: STM Mixer Stereo vs Mono

Post by Music Manic »

Ok I’ll try with assigning some devices to DSP in the SDK.
Do you just assign the DSP and save the device or is there anything else I need to do?

Thanks again
fra77x2
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Re: STM Mixer Stereo vs Mono

Post by fra77x2 »

i think it is just this.
fra77x2
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Re: STM Mixer Stereo vs Mono

Post by fra77x2 »

the best way to check for phase problem is to record the file and observe in an editor. is it still sample accurate?
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valis
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Re: STM Mixer Stereo vs Mono

Post by valis »

Are you trying to cancel two stereo channels against each other? Or both sides of a single stereo channel?

The 'phase' locking on each mixer is different. On micromixers they often can stay on one mixer if you use smaller channel counts, and as you expand up the channels will be phase accurate in groups of 8 (or 4 stereo) if memory serves. So to cancel two separate stereo channels, using two channels next to each other, enabling the phase lock button, ensuring you have no inserts, and then it still comes down to how you're flipping the phase. I would do it in the DAW, simply inverting one half of the file (say R chan) and then sending that directly into the mixer. HOWEVER, for that to 'cancel' you would have to SUM that somewhere to mono as well!

To phase invert a mono channel is easier, as the mixer should have that. But again you can eliminate any DSP issues and work up from there by first taking a mono SINE wave file, duplicating that file and inverting that (phase, not time) and sending both out bordering ASIO channels (say 1/2) as mono tracks in the DAW, and into mono channels in the mixer. Once again enable the phase lock on the mixer, and reduce the number of channels to the minimum, and then work up from there. In this case, a stereo output bus won't matter, as the MONO signals should cancel if all else is handled properly.
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Re: STM Mixer Stereo vs Mono

Post by djmicron »

Hi, I tested it on Xite and on Scope PCI with STM 2448, it's not a DSP allocation issue (anyway on PCI it's not possible to allocate on specific DSP, but only on same DSP), it's a normal behavior of the stereo sum when pan is left and right. Try to do the same with two mono tracks, if the pan is centered on both tracks, then the phase cancelation will be full, but if you spread the pan left and right, the phase cancelation will not work. You can obtain the phase cancelation on a stereo channel by inserting the StereoPan effect and centering the two pan potentiometers in the middle, or in the same exact position.
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valis
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Re: STM Mixer Stereo vs Mono

Post by valis »

If you're panning mono tracks left & right, how are you reversing the pan so that you can phase cancel? By sending the outputs from direct outs?

I think this is a process issue, rather than a mixer issue.
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Re: STM Mixer Stereo vs Mono

Post by djmicron »

You can't phase cancel using direct outs, because the signal must be on same path to be subtracted, this is why it doesn't work when you are setting pan left and right, one signal is going to the left signal path and the other to the right one. Do the test as i explained in my previous post to exclude the DSP sync issue and in the case of DSP not in sync, it would fail even with mono.
For stereo tracks independent panning there is an insert effect called stereo pan, use it for the test.
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valis
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Re: STM Mixer Stereo vs Mono

Post by valis »

I think my point is that 'panning' implies a stereo bus, even if the source is a mono channel/signal.

I've followed this thread and it's still unclear how/where the sum is being done as a mono (master bus) chain.
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Re: STM Mixer Stereo vs Mono

Post by djmicron »

valis wrote: Sat Nov 05, 2022 2:03 am I think my point is that 'panning' implies a stereo bus, even if the source is a mono channel/signal.

I've followed this thread and it's still unclear how/where the sum is being done as a mono (master bus) chain.
when the source is mono and the signal is sent to a stereo bus, if the pan is centered then it's sent half on left channel and half on right channel, this is why when sending two separate mono sources to the master stereo bus and one of them is phase inverted and each of the mono source is pan centered, they will null, but if we change the pan setting on one of the two mono sources the null test will fail, because the signal on the stereo bus will not match.
On the other side, when using a stereo channel on the STM mixer, we have two mono sources linked to the same volume fader and hard panned left/right and the pan control on a stereo mixer channel on the STM is a crossfader like in a Dj mixer, it excludes the left channel when moved to the right side and the right channel when moved to the left side and to have individual pan control on a STM stereo channel, we have to use an insert effect such as the Stereo Pan located under the mastering folder and it allows to individually set the pan for each of the two mono signals.
It's a different story if we want to phase cancel against two stereo mixer channels, in that case if we invert the phase on both left and right channel on one of the two, the NULL test will work.
This is not specific to Scope mixers, this is what happens even when you have a stereo source on your DAW of choice.
Also it has to be noted that when in Scope there is a sync issue between different DSPs, it's a matter of a couple of samples and a NULL test will produce anyway a big amount of cancellation.
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valis
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Re: STM Mixer Stereo vs Mono

Post by valis »

I understand all of that, I'm trying to understand the process in this thread to see where there's an issue with phase coherence that is NOT a byproduct of the process used, if that even is the case.
Music Manic
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Re: STM Mixer Stereo vs Mono

Post by Music Manic »

Hi guys

I've just tested a few things and it's not a phase problem. It's the architecture of how mixers are built. the Ableton mixer shows the same problem.
If you phase one side of a stereo channel. Scope mixers or DAW ones it shows that there is just a 180 degree correlation between Left and Right nut funnily no phase cancellation when sent to the master out unless you mono it.

I find this structure weird but am getting my head around out. Please look at my pics if I'm not making myself clear.

Thanks
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fra77x2
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Re: STM Mixer Stereo vs Mono

Post by fra77x2 »

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valis
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Re: STM Mixer Stereo vs Mono

Post by valis »

This is what I was saying, expecting a null to occur when the busses are not architected that way is a bad process, not a bad result.
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