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I am using Ubuntu Studio 18.04 on a desktop PC. I am getting a high pitched continuous static noise from Roland DS-30A active studio monitors connected via s/pdif to a Focusrite Scarlett 6i6 2nd generation USB audio interface.

The noise starts just after the ASUS bios logo appears and the sound disappears completely after I login to US. After login, the sound is perfect but the static occasionally happens even more loudly if I turn the monitors off and on again while the PC is running [Edit: further investigation reveals that this happens randomly when Jack decides to stop rather than just when the monitors are switched off and on again].

The quieter short period of static at boot up happens regardless of whether the Jack Sink (pulseaudio) bridge is activated.

ASUS PRIME A320M-K. Ryzen 7 1700X. Nvidia Geforce GTX 1050.

I can supply more hardware info if required.

Any ideas what might be causing this?

UPDATE

The problem is that Focusrite doesn't support Linux so there is no official driver. However, the Focusrite 6i6 2nd generation device is class compliant and thus should "just work" with Linux, which it does for the most part. The static sound is fairly quiet during boot up but it is much louder when the monitors are switched off and on again while the PC is running. Too loud to be just normal system background noise--it is uncomfortable to listen to for more than a few seconds,

On further investigation, what seems to be happening is that the very much louder static noise is caused when the Jack Sink (Pulse Audio) bridge fails because Jack stops for some reason. When the loud static is sounding, the Jack Sink (Pulse Audio) bridge is replaced by "Monitor of Dummy Output" and this is what I see in sound settings:

Sound settings when static noise is sounding.

And when the sound is normal, this is what I see in sound settings:

Sound settings when normal

If I restart Jack from Ubuntu Studio Controls when the loud static is sounding, it disappears after a momentary "pop" and normal audio resumes.

So, there appears to be some instability in the Jack-Pulse audio bridge?

2 Answers 2

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The Focusrite Scarlett series of products is known to have some issues with the Linux kernel included with 18.04 LTS. There are two things you need to do which have shown success for people with the Focusrite Scarlett products:

The popping when starting/stopping Jack and the PulseAudio bridge is, unfortunately, just the nature of changing sound servers from PulseAudio to Jack.

Basically, what is happening is Jack is taking-over as the primary audio server, and has to kill PulseAudio in the process. Once that's done, as long as the PulseAudio bridge is selected in Ubuntu Studio Controls, it has to start PulseAudio and add it as a "device" inside of Jack, and PulseAudio sees Jack as its output device (what you see in the system audio menu). Basically, PulseAudio becomes a Jack-aware application that acts as if it were an audio device. It's not clean, but it works. I experience this on my Behringer UPhoria UMC404HD all the time. It's just the nature of Linux audio.

If you have installed and opened Carla and selected the patchbay tab, you'll be able to see exactly how Pulse is connected to your system outputs and inputs via Jack. I personally find this a very simple, easy-to-use and visualize interface.

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  • Thanks. I eventually discovered that the default Focusrite spdif output volume slider was on full and I am guessing the signal was too powerful. Even in Windows, with the official driver, the default spdif out volume was deafening. Almost blew my studio monitors out of the water. The internal routing of Focusrite Control is a luttle complex initially. I eventually discovered how to lower the spdif output volume in Focusrite Control (in Windows but the settings are remembered when booting into Linux). Eventually, I switched to the Focusrite analogue outs and have had no problems since.
    – Chris
    May 9, 2019 at 18:43
  • Glad to hear it! I just addressed the popping you hear when the sound server switches from PulseAudio to Jack. If you could mark this as answered, that would be spectacular. :) May 9, 2019 at 19:30
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This problem is very likely linked to your sound card.

The start-up static is nothing but the start-up sound of Ubuntu. The static you are listening while turning on/off the monitor is nothing but system sounds.

One way to fix this is to find a suitable and working driver for your sound card. This should really fix your issue.

If the problem still persists, chances are your sound/speaker hardware might have been damaged.

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  • In Ubuntu Studio system sounds are usually disabled by default.
    – mook765
    May 8, 2019 at 16:50

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