Frequency oscillation with some PSUs

[RetroLoom]

On at least one of my computer builds noise is generated when using the ThrottleBlaster and PWM2STPCLK devices. I have mentioned this on other issue threads but I decided to have a dedicated one since finding a solution. When using a more customizable PWM generator I learned that the noise directly correlates to the PWM frequency. This makes sense because you can actually use PWM as a tone generator this way. I found setting the frequency to 60-100hz was able to create a frequency that was naturally filtered or too low for my PSU. With non extensive testing I found that this does not affect the behavior of the PWM or throttling so could possibly be used as a default.

Here are some videos demonstrating the affect of changing the frequency the pitch shifting along with the changes.

https://github.com/user-attachments/assets/7e597425-c28a-471a-9160-4fe78ae61327
This first video starts at around 9.5khz and cycles down. There are certain cycles that can be heard more clearly than others.

signal-2025-04-13-154610_003.mp4

[scrapcomputing]

Thanks for looking into this! Lowering the PWM frequency to < 100 Hz seems to be a good way of getting rid of the noise. Not sure what the threshold is before we start running into issues though. Have you tried very low frequencies, like 10Hz ?