Weird knobs behaviour in a slim phatty

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pandauer
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Joined: Tue Oct 20, 2020 3:35 pm

Weird knobs behaviour in a slim phatty

Post by pandauer » Tue Oct 20, 2020 4:05 pm

Hi!
I just bought my first slim phatty, well, my first synth :D , and I am having some strange problems with the knobs when the SP is connected through usb to my macbook air.

This is my setting, at the moment

- slim phatty
- behringer UMC404HD sound card
- arturia keystep

SP is connected through DIN cables to the sound card (SP midi out to UMC midi in, and UMC midi out to SP midi in).
I have a jack cable going from SP audio out to "line in" in the UMC sound card
The arturia keyboard is connected to my macbook via direct usb, as well as the soundcard.

after few seconds I turn on the SP, knobs start working in a weird way: red leds do not follow well the movements, sometimes overshooting or going backwards, very noisy movmeents. The sound produced by the SP is also strange.
If I unplug the usb cable of my soundcard from my mac, then knobs work well. If I restart the SP with all cables plugged in, it works well for few seconds, then the problem comes back again.

I do not have any issue if I plug the keystep to the SP through midi DIN cable and plug my headphones, so without other connections to soundcards or to the macbook air.
I have tried also using a Behringer Xenix USB mixer instead of the soundcard, but have had the same issue.

Everything (SP and UMC) is connected through a power strip to the wall plug. I am not sure if this can be due to a ground problem with the wall plug, as sometimes I feel little electric shock if I touch my mac and I don't wear shoes :shock:
However, the knobs issue appears also when my mac is on battery and not connected to the plug - well, still with the SP and UMC plugged to the same power strip.

Has anybody experienced a similar problem? Do I need any additional gear (DI box maybe?) to prevent this issue?
Any suggestion?

Thanks a lot in advance!

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stiiiiiiive
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Joined: Tue Aug 30, 2011 2:58 pm
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Re: Weird knobs behaviour in a slim phatty

Post by stiiiiiiive » Thu Oct 22, 2020 5:21 pm

Hi Pandauer.

At first, as it happens with USB but not with DIN cable, I thought about MIDI feedback.
When you move the Slim knobs, it sends MIDI messages to your DAW. Your DAW redirects them through MIDI to the Slim. Kaboom, MIDI feedback. You may have to check that your DAW isn't "thru-ing" the incoming MIDI messages.

But you also talk about wall vs battery operated computer. So you may want to get inspration from this thread.

Hope this helps.

pandauer
Posts: 2
Joined: Tue Oct 20, 2020 3:35 pm

Re: Weird knobs behaviour in a slim phatty

Post by pandauer » Mon Nov 02, 2020 12:47 pm

Hi Steve,
it was MIDI feedback, as you suggested!
I fixed it in ableton and now I don't have that issue anymore, thanks a lot!!!

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