#46 Re: Digital.
Posted: Sat Sep 14, 2019 9:46 pm
Of course, though it's not a piece of kit but a design for DIY building. It has a valve-based delta-sigma (or sigma-delta) core. There's a thread about it on DIY Audio;
Semantics to some extent but the FPGA operates solely in the digital domain and you could choose to send the data from it to a decoder or do something else with it so I don't really see it as a core element of the actual decoder - it essentially just doing ASRC. In the design, the derivation of an analogue signal happens with the valve-based DS cores.
I too will be interested in how it sounds and look forward to reading how you get on, BUT the pedant in me still thinks that calling a sigma-delta decoder a DAC, while true in the sense that it converts a digital signal into an analogue one is rater misleading in the sense of the original question "Just out of interest Ray, is there a valve DAC without any DAC chips ?". You can decode SD with a resistor and a cap because all the hard work is done up stream converting a multibit signal into a possibly noise shaped single bit stream. To me in the context of the question you would expect a black box with i2s on one side and analogue on the other to be the DAC. Correct me if I am wrong, but that's not what you have here.Ray P wrote: ↑Sun Sep 15, 2019 11:27 amSemantics to some extent but the FPGA operates solely in the digital domain and you could choose to send the data from it to a decoder or do something else with it so I don't really see it as a core element of the actual decoder - it essentially just doing ASRC. In the design, the derivation of an analogue signal happens with the valve-based DS cores.
In fact, the project I'm embarking on dispenses with the FPGA module completely but of course it still uses silicon in the clock and data management elements.
Still, in my book it is truer to the term valve DAC than a conventional IC based DAC that just happens to have some sort of valve-based circuit attached to its outputs - in that scenario the valves only ever see an analogue signal and have no part in the 'conversion' from digital to analogue.
Anyway, it'll be interesting to see how it turns out and, depending on that, might make an interesting exhibit at next year's Owston event.
Yes and thanks, it'll be an interesting journey. I'm starting with an open mind rather than an assumption that valves will automatically be better but it'll be fun to do something other than the usual modern ESS/AKM or NOS legacy chip type projects that seem to be everywhere. I enjoy this hobby as much for the building as the listening.
Like I said we're talking semantics and ultimately the points aren't that important but this is a 'valve DAC without any DAC chips', you just have to feed it the correct digital data, which in this case is SDM/DSD as it won't decode i2s/PCM - AFAIK there's nothing that defines a DAC as having to be suitable for PCM data? Whether you feed it with 'native' SDM or you choose to derive it from some other format, whether an FPGA ASRC type function on the front -end or something upstream like HQ Player doing a similar function is, to me, a separate issue.Nick wrote: ↑Mon Sep 16, 2019 3:03 pm ...BUT the pedant in me still thinks that calling a sigma-delta decoder a DAC, while true in the sense that it converts a digital signal into an analogue one is rater misleading in the sense of the original question "Just out of interest Ray, is there a valve DAC without any DAC chips ?". You can decode SD with a resistor and a cap because all the hard work is done up stream converting a multibit signal into a possibly noise shaped single bit stream. To me in the context of the question you would expect a black box with i2s on one side and analogue on the other to be the DAC. Correct me if I am wrong, but that's not what you have here.
That's sort of my point, DSD and DS DAC's convert the PCM into a bit stream that allows simple conversion to analogue. In your case, you are doing all the PCM to bit stream conversion "elsewhere" so I regard the majority of the DAC in this case as being "elsewhere".While we're in the general vicinity of delta-sigma processing its maybe worth thinking about how a mainstream delta-sigma DAC chip functions with PCM data.
Whereas I consider that those DACs have a load of other stuff added to them so they can accomodate other data types - the 'DAC' is where the conversion takes place.Nick wrote: ↑Mon Sep 16, 2019 8:21 pm That's sort of my point, DSD and DS DAC's convert the PCM into a bit stream that allows simple conversion to analogue. In your case, you are doing all the PCM to bit stream conversion "elsewhere" so I regard the majority of the DAC in this case as being "elsewhere".