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I'm having a rather peculiar issue with the playback on my io device. Basically, every minute or so the sound becomes laced with a harsh digital distortion for a few seconds (between 3 and 10). It's easier heard than explained, so I've posted a sample of the sound here.

I'm using a Mackie Onyx 1620i with a 003 serial number. My computer is a Lenovo X230 Thinkpad with Ubuntu Studio 18.04 LTE. The two are connected via firewire. It's important to note that my laptop doesn't have a dedicated firewire port - I'm using a removable 2 port fire wire card on my express port (a 2 Port ExpressCard 1394a from StarTech.com). Though I'm usually only using the Mackie with Ardour 5, it also occurs in other applications.

The issue only occurs when outputting audio from the Thinkpad to the Mackie. There's absolutely no issues with recording audio to the laptop. Though I've had some issues with the Mackie with other Ubuntu Studio kernels, it's currently working without any drivers in virtually every application, and automagically connects to JACK when I plug it in. There have been a few rare occasions when the issue doesn't occur at all.

Finally, so far this problem occurs with this system only. I frequently use the Mackie with a Macbook Pro and a Mac Mini (through a Firewire to Thunderbolt adaptor, no less) and there's never been any problem with the playback.

Troubleshooting things I've tried: - Both firewire ports on the ExpressPort card - Both ports on the Mackie - Different firewire cables - Both Ubuntu studio kernels (low latency and regular) - Both ALSA and JACK drivers at various sample rates

If anyone has encountered an issue like this or has any leads, I'd love to hear them.

Pang
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Zurn
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1 Answers1

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The great user OvenWerks on IRC has solved this for me:

The sound is likely two sampling frequencies mashing in and out. Using Pulse, I've turned the profile for all internal audio devices to "off",and, so far at least, there's been no occurrence of the issue after a few hours of playback through ALSA.

For anyone using JACK with the pulse->jack bridge, then the same fix will effect jack as well. If using ubuntustudio-controls to start jack, it will already fix pulse to work with jack.

Explanation: The problem is that pulse takes it's sync from the first alsa device it finds (normally the internal audio) and uses it for sync. The pulse -> jack bridge binds jack to pulse in a closer way than it should (because the bridge was never properly finished) and so removing phyical devices from pulse allows pulse to use jack for it's sync. If pulse has two sources of sync they will clash even if they work at the same rate

Zurn
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