Serious talk: No DAC chip, but a FPGA? - Page 3 - diyAudio
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Old 27th October 2016, 09:20 PM   #21
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Default Thanks!

Thank you DPA,

This is helpful and provides some reassurance that I was on the right tracks.....As I am looking at a commercial application which performs multiple functions within the FPGA....Crossovers, Eq, limiters, room / speaker measure and correction, delay plus others, and I need up to 16 channels, so its well worth the serious investment in R&D....In the long run way cheaper than buying 16 channels of all these different functions and attempting to assemble them into an active studio system....

Thanks again and all the best
Derek.




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Originally Posted by DPH View Post
I want to be forthright--we're talking something seriously non-trivial. So to tackle your question thoroughly is beyond my scope here.

Just to get us off on the right foot:
FPGA = field programmable gate array. The breadth of options here are dizzying. But, in short, you'll be looking at something with a large amount of programmable logic with a moderate amount of fixed logical blocks.

It allows one to bake into logic/pipelines algorithms that would otherwise require interpretation by a more general-purpose processor and it's baked-in data pipelines.

ASIC = application specific integrated circuit. This is really a catch-all term for fixed logic circuits. So that's everything from a DAC chip, to a human interface chips in your cell phone, to fixed pipeline audio DSP chips, to gigantic stream processors used in modern workstations/supercomputers.

So in more easily couched terms, with an appropriate FPGA, one could flesh out a DSP pipeline (resampling/noise shaping/etc) and perhaps even a lot of the control logic for a downstream DAC. It's still in the digital domain, however, within the constructs of the FPGA, although that distinction get really blurry really quickly when you're talking about mixed-mode signals.

So if you're really, really, really gung ho about a new DAC topology/implementation, you're going to have to go to a bespoke solution (where you'll need that FPGA), which you'd better *really* know what you're getting into (I don't pretend I do).

If you look hard at the top-end DAC chips available from the likes of AKM/TI/ESS/Cirrus/etc, it makes it hard to say, "I can do a better DAC than them". But implementing one of these chips and squeezing every last drop out of its performance is no child's play either, given the PPB error rates being specified. The analog circuitry, PSU, and layout need to be all there to realize the full benefit of those DACs.
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Old 27th October 2016, 09:26 PM   #22
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Conceptually I like the idea however I don't think this is the sort of thing that happens over night. That's not to discourage one from doing such a thing.

The ideal DIY scenario would be someone who has some knowledge of programming a chip like a Spartan6, sell boards with a flashed chip designed to perform filter and waveshaping functions. Allowing the end builder incorporate additional components - power, output state, etc, however they like.

The main goal here is to replace a conventional DAC chip with an FPGA.

Last edited by milezone; 27th October 2016 at 09:35 PM.
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Old 27th October 2016, 09:31 PM   #23
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Looks like i stand corrected.

dave
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Old 27th October 2016, 09:37 PM   #24
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If you really want to get the absolute most out of the implementation (and if you're going to go through the trouble of a bespoke solution, I'd hope that's the ultimate goal!), then you really need to have absolute control over the entire design. Leaving parts of it up to the builder seems counter that goal.

Overkill--I don't think your stated aims really necessitate a custom DAC. The advantage in the latter is the control of the implementation of the DAC itself, rather than large-scale integration. I'd be wont to spend my money on a modest, albeit quiet desktop computer with a pro-level soundcard and pay someone to configure it appropriately for your workflow.
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Old 27th October 2016, 10:00 PM   #25
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Thanks again DPA,

I'm happy the bespoke FPGA route is the best choice.

The end product will not be for my own private use or DIY, pure commercial ROI at the end of the day and when combined with my active loudspeakers it makes for a very compelling high performance package.

Looks like its a good 12 month R&D....Even working with a top flight designer who has track record here....He has completed a very ambitious 64 channel DAW incorporating FPGA's and whole bunch of other goodies!

Anyway time will tell and thanks again.
Derek.
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Old 27th October 2016, 10:07 PM   #26
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Good luck to your project, Derek!
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Old 27th October 2016, 10:28 PM   #27
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Might I ask which DAW you're referring to? Is it Merging Technologies by any chance? Their work is very interesting to me.
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Old 27th October 2016, 11:12 PM   #28
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Sorry milezone I cant say as I am under an NDA.

All the best
Derek.
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Old 27th October 2016, 11:39 PM   #29
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Derek,

A lot of the functions you have listed there are better served with DSP. You can brute force them with loads of logic gates, but you start needing big chips and big R&D budget for no real gain when grunt is cheap. Of course to confuse things you can put DSP cores in a lot of FPGAs these days so the line between hardware and software gets blurred very quickly. But I would seperate processing and conversion into two problems and pick the right tech for each.

And if you are making less than 10,000 of them a year license as much as possible otherwise you burn 100k in R&D for something that's available for pennies or open source.
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Old 27th October 2016, 11:46 PM   #30
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Hi Derek - I find myself in agreement with Bill here - take a look at Analog Devices' DSP offerings (SHARC) - these get used by other commercial entities doing what you look to want to do.
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