FPGAwars: Exploring the Open Side of the FPGAs

> Every official website in the country is in the four languages

This is plain wrong. I could give you (just making a quick Google search) hundreds of examples where you can see it's not true. Co-official languages are just second-class citizens here. Not only dozens of official web sites are Spanish language only, but also those who offer language selection mostly just change the menu option titles, but the actual content is only in Spanish.

Even Spain's anti-covid mobile application (Radar Covid) -whose UI is just a couple of messages, nothing very hard to translate- got translated to all the official languages only recently.

https://portal.mineco.gob.es/gl-es/comunicacion/Paxinas/defa... (I chose "GL", but the news are still in "ES")

https://www.casareal.es/GL/Paginas/home.aspx (the same)

https://industria.gob.es/renove/paginas/index.aspx (where's my language menu?)

https://www.rtve.es/ (no languages for our public televison website?)

This last one is a good example, because everybody, regardless of his language, funds RTVE through taxes, yet its live contents are mostly Spanish language only.

And we can find similar examples for the other topics. But no, I don't care what they do or speak in Murcia, I just want to have the same rights that someone from Murcia has in my region.

For beginners coming from software side, I highly recommend the official lattice boards like ice40 hx8k (by axelsys).

They are cheap and are supported by the FOSS toolchain. So you won't waste money or wrestle with crappy and/or expensive commercial tools, and can concentrate on learning FPGA.

The real issue seems to be that audiophiles want something that is unrelated to actual perceptible sound quality. Instead people want to think that the sound is good, and they have some expectations as to what might make sound a little better. This is why there is garbage like silver-plated cable, expensive power cords, etc. People expect amplifiers to be heavy, so amplifiers use big transformers and such and end up heavy.

Unfortunately, this phenomenon seems to make it quite hard to find genuinely well designed equipment. I would love to get a small A/V receiver with high efficiency, the ability to drive a load of varying impedance from 1-16 ohms (possibly frequency dependent), and better linearity and noise characteristics than I can perceive. Actually buying such a thing is not so easy due to all the snake oil and the fact that almost no one reviews equipment on any objective axis.

There is one genuine complication that I’m aware of: analog audio connections tend to be old, bad designs. RCA is single-ended. XLR is a decent design, but it’s rare in home audio. Speaker wires, in all their silver-plated glory, aren’t twisted. So inductively coupled noise is everywhere, especially at 50-60 Hz. Ground loops are hard to avoid. Unlike RF, audio should have a flat response down to 20 Hz, so cheap, small tranformers are out of the question. Nice isolation hardware isn’t that expensive, but it would still add up if you wanted to build an A/V receiver with a bunch of isolated inputs and outputs. With professional systems, you are much more likely to encounter differential signaling, but you are also likely to have very, very long wires and rather low signal voltages from microphones and such. This can result in unpleasantness like AM radio becoming audible if you have non-linearities that might accidentally rectify the radio signal.

I would like to see the audio world move to digital signaling for everything, but good luck getting everything to interoperate.

Audio DACs are actually a lot more complicated than you might think. Human hearing is very sensitive to non-linearity and noise, especially certain kinds of noise. In terms of raw performance, the linearity and noise requirements were definitely the most demanding as far as state of the art when I was doing research. They're certainly still tougher than anything in the RF space (specifically cellular, bluetooth, and wlan). Also, because most of them use delta-sigma modulators, the jitter requirement was also very stringent, though high-performance digital and RF may at this point need lower jitter than audio.

Unfortunately a lot of the advancement, especially in the high end space, is proprietary. I read a somewhat vague article about some of the more recent innovations, and one that stood out was the need to set the Initial Condition of the Delta Sigma Modulator in a specific way. Delta Sigma quantization noise is notoriously poorly behaved, and because of its periodicity, it was actually perceptible even at its lower levels.

I would agree that audio DACs are indeed a "solved" problem, but at this point so is pretty much everything in integrated circuit design. Most advances in design are very incremental. The need for innovation comes from the continued push to reduce power and cost. Eventually you have to change process node - smaller transistors means a smaller die and lower cost, and also lower power for many circuits. That tends to be very challenging for a lot of mixed-signal circuits because the smaller transistors are worse in analog domains. You end up having to play a lot of tricks to make things work, but its pretty well understood and nothing revolutionary.

(obligatory reference to employer's parts catalog: https://www.cirrus.com/our-technology/audio/hifi/ - I'm prepared to say that 24/192/114db should be good enough for anybody!)

So you're right that within the industry we already have the analog side as re-usable IP. However, someone starting from scratch - and especially starting with a FPGA - would need a lot of analog design experience. Analog silicon design is an even more rare skill (we are, I think, hiring if you have this).

What we are generally doing is support features; headphone detect, power management, power amplification (built-in boost converters etc), as well as post-processing and EQ. You can use EQ to compensate for the nonlinear response of tiny speakers in mobile phones.

(An odd side effect of the hardware pipeline and my role in software support is that anything you can actually see on the public website is very out of date compared to what's in development and heavily NDAd)

I'm still not clear why the OP wanted an open source DAC.

Here, on HN and similar places, people have strong bias toward scientism, making fun of audiophile cables and such, but the actual truth is, audio business is ultimately an entertainment business, and if, for some unknown (and potentially very subtle) reason something sounds better, no one really is willing to research the matter deeper, because, the research may become prohibitively expensive, with weak or no results all. Of course, there are general trends, like more linear DAC usually sounds better than less linear, but it is not always true. I mean, sometimes, two seemingly equivalent designs may sounds noticeably different, yet their physical measurement would suggest otherwise (which means, we are measuring the wrong thing).

I would love to know the answer to this for all the same reasons. Is there some actual special sauce or is the world of 'audiophile DACs' just the new 'Monster Cable' FUD?

I wondered if there might be, but did you post the right link? I can't see anything about open source USB device implementations there.