Crackling sounds when playing ptb sine wave sound

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OS: Win10
PsychoPy version: 2023.2.3
What are you trying to achieve?: Play sound over headphones connected to Fireface UC soundcard

Hi everyone,

I have a weird audio problem: I try playing a sine wave sound using PTB and in-ear headphones by E-A-RTONE which are connected to an external Fireface UC soundcard. When I play the sound over the computer display speakers, the sine wave sounds normal (smooth, uniform sound so to say), but when I switch to the external soundcard, it sounds crackling. Any idea what might be happening there?
I’m currently using a sampling rate of 44100, I’m playing the “A” sound for 0.1 sec, and I’m using ASIO as a driver (at least I think I do this, the whole sound implementation is a bit confusing for me).

Thanks in advance for your help / ideas!