One of the attractions of buying at the bottom end of the electronics market by mail order from China is that you never quite know what will come your way. Sometimes it’s a diamond in the rough, while with others it’s a mess. Occasionally along comes something which should work but doesn’t, and that’s the moment when you wonder if you could fix it. [Nyanpasu64] had just such a device, an HDMI to VGA converter with audio that didn’t work. What could be wrong?
The HDMI to VGA chip has an onboard audio digital-to-analog converter (DAC), and it’s a delta-sigma design. This type of DAC is frequently used in audio applications because it works by shifting its switching frequency many times higher than the input sample rate, thus reducing considerably the distortion. This one wasn’t performing as advertised though, and the problem turned out to be that switching frequency being all over the output. Clearly the filter wasn’t working, which led to the design of a new filter. The write-up is therefore an extensive dive into filter design, and in part also a discovery of the effect of impedance on them.
For a super-cheap module to cause so much work, one might ask why not simply spend a few more dollars and get a better one. But had they done that we wouldn’t have seen this write-up, so we’re sticking with team cheap.
We’ve looked at audio DACs, in the past.
Chinese are masters at cost cutting. Shave 0.07 cent of here, shave 0.05 cent off there. The cost cutting takes R&D, which costs money in itself, but it’s worth it if you sell millions of devices. And then they market aggressively, which means that the guy who is able to offer the lowest price for a product, is the guy who gets most or all of the sales.
The net result of that is that there’s an almost lineair relationship between what you pay and what you get.
I still find it amazing.
There are also adverse effects of course. The biggest one maybe that the aggressive competition means that you simply cannot rely on that the company that you bought your thing from still exists next week.
There are also lots of scams and scammers. But I consider that a separate problem that’s not really related to the above.
Cost cutting is the art of producing a product that still does what is advertised but with less production cost. Quality may be lower. Lifespan, RFI, etc… all may be questionable. But it should still arguably accomplish the task it was advertised for.
Selling something that does not do what is advertised… sounds more like fraud to me.
I bet a lot of people buy those things and don’t even use the audio. Simply dropping the jack and any audio-only components and then marketing it as video-only would have been greater cost cutting yet.
anecdotally, in my experience, the scams hamper the relationship between cost and quality. the only reason i like temu is that i’ve experienced so many cases where i paid ‘full price’ from a ‘reputable vendor’ and gotten basically the same low quality
See also, amazon.
It’s just scummy behavior. It’s theft of other people’s work and the only research they do is seeing how much they can rip people off before people turn their back on them or learn of their schemes. They should 100 percent be banned from international trade and be forced to eat the rotten fruits of their labor.
An unrelated thing. I can’t find where to report this… But since today Safari is asking me if I want to allow downloads from Hackaday every time that I open a page on hackaday.com. I do not allow downloads if I didn’t choose for one, so I don’t know what the site wants me to download. But it strikes me as very odd, and makes me think that maybe something has been hacked?
Sounds like your browser is infected with the feenglerhoppler worm. You need to download a good deburbller tool and run a full scan. That should make it all better.
Literally opening the site means you’re downloading data. Text and picture at the very least….
Sounds like you may have a virus or something. Does it do that anywhere else?
Open the browser console (Ctrl+Shift+I) and eg look at network traffic/requests to see what “is trying to download”
Compare with another browser / on another computer to see if you’re infected or something (some plugin/userscript/etc is injecting something).
This is a beautiful piece of equipment.
“One of the attractions of buying […] electronics […] is that you never quite know what will come your way.”
This quote makes more sense with the ellipsis. Nowadays, you generally get surprises – no documentation, no schematics… Unless it is Open Source Hardware (OSHW) you buy.
Vote with your money.
I was having similar issues, since I had a Video Projector that only had a VGA input. After searching long for a HDMI to VGA converter that also has analog audio, I gave up. As I tried to watch some streaming services and they all have DRM active it was additionally difficult.
I settled on the Bluetooth of the Streaming stick and got myself a cheapo Bluetooth speaker, paired it and accepted the result. The one HDMI to VGA converter (without audio) that I had worked “good enough” for the Projector.
Does the Switch also have Bluetooth, for audio?
That’s not how delta sigma DACs work. But more importantly, that’s not why they used one. It’s because it’s cheap to implement: all digital and standard push-pull output pads, and only a simple passive filter needed for each channel.