MiSTer FPGA Forum

I didn't use to have this problem. I tried switching audio cables too. For some reason, When I power on my Mister, or reset it in some way (which includes loading any new core), I get a momentary but pronounced pop in my speakers. No other device plugged in to the speakers exhibits this behavior. This is audio through the 3.5mm 'headphone' type jack. Settings? Ideas? Thank you.

Not sure why this wasn't happening before, but yeah when loading a core or resetting your MiSTer, this is normal (at least, it has been for me during the brief time I used aux audio. I've switched to TOSLINK).
Maybe you turned off noise cancellation on your speaker.

It's normal with the analog output on the MiSTer. I get a pop or click upon startup and initializing a core.

Have you tried measuring the output for DC offset? If there's a large offset this can cause pops and clicks like when it's initialized, which would be my guess.

A DC offset when it's triggered or removed will cause a pop or click when the output is instantly changed to the opposite state. It can theoretically be filtered out by a deep high pass filter.

EDIT: I found this explanation - very similar to a DC offset - although this wouldn't explain why pops aren't also present via the digital output.

The reason is that when a core's running, the audio "zero" point is half way between minimum and maximum, so that it can swing both up and down to produce the audio waveform. The core is constantly outputting alternating high and low pulses which are averaged out by a simple filter on the IO board. The ratio of high-to-low pulses determines the output voltage, but when there's no sound the ratio will be 1:1 and the output level will be 50% of maximum.

As soon as you reconfigure the FPGA by changing core that process stops, and the output voltage swings immediately to minimum (or maybe it's maximum!) for the duration of the configuration process, after which the newly-loaded core brings it back to the half-way point. Both transients cause an audible pop.

lagerfeldt wrote: ↑Mon Mar 18, 2024 8:53 pm

EDIT: I found this explanation - very similar to a DC offset - although this wouldn't explain why pops aren't also present via the digital output.

Thanks for finding and posting that explanation, so the output does D/A conversion via PWM. Oh well. I also changed to a TOSlink D/A device because of these annoying clicks.

The reason why it's not present in the digital output is probably that the optical output is not PWM: it carries numeric values and "knows" what zero is.

This might be fixed by having a newly loaded core gradually go from this min or max value to the center value, say during the first few frames, so it becomes inaudible.

The other way around, when exiting a core, would be tricky or maybe not even possible, depending on how the reset button works.