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Comment by jdfellow | Hacker News Reader

Isn't Delta-Sigma and PDM exactly how DSD works? In fact, I think Sony originally came up with DSD as an intermediate representation of PCM in one of their DACs and then Sony & Phillips got the harebrained idea to use it in SACD. That is to say, a simple DAC for DSD is just a capacitor functioning as a low-pass filter, without any other components.

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Hardware is getting more and more esoteric, so the delight and surprise should be expected, and encouraged. :)

I would claim that 70% of software engineers would love taking an electronics course. It's like programing, with electrons.

I suspect the next link in the cycle will be how you can make music on an old AM radio, if you attach a length of unterminated wire instead of a cap!

> I would claim that 70% of software engineers would love taking an electronics course. It's like programing, with electrons.

I very much think all software engineers should take an electronics course. At least an introductory one. Knowing how things work will improve your code, and will give you an alternate way of thinking about programming problems.

But I'll admit my bias: I came to programming by way of a digital electronics course as a child. Since I was a child of a poor family, I couldn't afford to actually do electronics projects at home, though (this was well before everything got so inexpensive), and shifted to programming because you could do that for free if you had access to a computer.

I’m curious : how would knowing more about electronics improve code ? To me, the basic properties of electricity are hidden behind the higher level hardware components code can interact with

Probably the same way exposure to different paradigms of writing software helps one become a better programmer - more abstract tools in your toolkit, more ways to think about how to solve a problem.

If you're ever dipping down into firmware level stuffs, it makes reasoning about things much easier. I can intuit whole systems, where my software only friends really struggle. Some firmware bugs are immediately debugged with a o-scope.

I spent an entire summer circa 2010 trying to rip the decrypted DSD signal off an SACD player via an FPGA. I figured the simple on/off levels would be easy to grab but I had not much success beyond being able to visualize it on a scope. Was trying to get at the high resolution, multichannel tracks for a Lord of the Rings soundtrack.

I spent somewhat inordinate amount of time around 2010 by designing a Class D PA amplifier that used DSD-like bitstream internally. The idea was to convert analog input signal into this bitstream by what amounted to somewhat convoluted sigma-delta ADC, process that with FIR filter in digital hardware and drive MOSFET H-bridge with that. The thing ended up ridiculously complicated (with somewhat impressive amount of SRAMs) and totally non-practical (through hole 74HCT and GALs, which worked out to something like 15 3U eurocards). I never got to complete the board layouts, much less building it, which is probably a good thing.

As I understand it, the really nice modern class D amplifiers use feedback internally, which more or less eliminates using a pre-computed DSD-like bitstream as a good option.

On the other hand, FPGAs and really fast microcontrollers are a thing now, so you could probably get a chip with a nice internal ADC, digitize the output voltage, and use an actual computer program to drive the H bridges, thus making an extremely non-cost-effective class D amplifier :)

The “high-end” PA Class D amplifiers (the kind of thing that is used in clubs on Ibiza and such things) have feedback loop and the feedback loop is closed in purely analog domain around the whole Class D amplifier, alternatively one can look at that as an giant SMPS with large slew rate, which is what that is (there is a bunch of anecdotal evidence around the losses in the output reconstruction/low-pass filters that apparently can reach temperatures that the solder melts, which is kind of problematic when in the chassis the board is mounted components down).

Issue with doing what I tried to do and FPGAs is that the overall architecture of this kind of DSP is perfect example of a thing that does not match the FPGA architecture. It boils down to ridiculously long shift register, few bits per tap of parameter data and reducing tree for the result, ie. most of that is ridiculous amount of 1bit SRAM cells.

And well, in the end I realized that idea, in not-even-that-fast-for-the-time ARM11TDMI and software and 24b samples at 96kSps (both of which is realistically a total overkill for this application), but without the DSD input (in theory the code that produced the output can be inverted and used to convert DSD to some sane representation, but well, I did not really care)

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