WavetablePi: Better PWM audio 

Getting different results on breadboards is not all too uncommon. Breadboards have really bad stray capacitance problems as frequencies increase. Generally on more premium breadboards they'll send a metal plate you can adhere via the sticky back which definitely helps the problem, but generally you're going to see the effects of capacitance even when no capacitors are there.

I never looked into how audio filters worked before and now I know! Thanks.

This big breadboard is trouble. Every breadboard is trouble, but tiny little breadboard maybe less trouble. I can hear strong mains hum. You can use a filter with corner frequency well in the audio band; and then pre-emphasize the audio in software to compensate. Indeed due to LTAS having a 100Hz corner frequency, a 150Hz 6db/oct filter might not be that far off base!

I love that your voice sounds like a muppet. It makes your video even more entertaining 😂❤

Very cool! Great explanation of PWM! I am now curious how other DACs work.

I wonder if they could add some noise shaping to the output code, to shift the noise up in frequency and improve the benefit of filtering.

Hmmm. I'd wonder how the signals would cope with a Clamp cap of some kind. 10pf or 22pf cap to ground from each of the signals, I don't know how well it would work but I'd be curious to find out. Normally I wouldn't add a clamp cap to audio lines but these signals are a little more "simple" compared to newer audio gear, so maybe it would help. There's also ferrite beads for high frequency stuff but I don't see them making a difference other than acting as a low resistance resistor. Another potential improvement would be to have an LC filter to try to clean up the power going into the pi zero itself, it shouldn't make a difference with a decent PSU but noisy power always goes directly into the audio quality. There is always more nitty gritty stuff like moving to a 4 layer design to give yourself more ground plane between the pi zero and the rest of the machine. Slap a video card beside a sound card and you'll hear the pixels. Now that I'm thinking about it there's a few things I'd like to see done given that these are PWM signals. Nothing I think would actually work but it would be fun to see what they would do, maybe even a tinkerboard, those have actually good audio.

Thanks

Hey, thanks for sharing. I build 2 devices myself ( 2 because i thought i made a mistake on the first), but when i connect it to my CT2940 nothing is happening. The DAC gets troubling hot and the pi is not booting. If i connect the pi to a normal powersupply i can see it booting up (of course it is not connected to the Soundblaster at that time. Any one build one themself and can share some troubleshooting ideas? I only have 3 CT2940 with Wavetable header…are they not compatible? Thx & Cheers

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