Understanding FPGAs

[raif71]

Yes Dustin told me each ESS Sabre chip run costs $250000. And they have no idea how they will even sound until they get it built, have it sent to them, and solder it onto a board. He said when they first got the 9038 pro back, and for the first time listened to the work that took them years to accomplish, they were all astonished how much better it was than the 9018S. They had no idea how much better sound could get. But it had to get redone a few times to work all the bugs out.

Does this mean that D10 (using 9018 based chip) sounds different than D10s (using 9038 based chip)? I think both DACs measured good and should not be audibly indistinguishable from each other, right ?

 

[Bamboszek]

Theoretically perfect DAC realized in FPGA would be always inferior to ASIC (so standard DAC chip).
FPGA is usually for general usage, fast prototyping or small production runs. ASIC chips can use special semiconductor process, optimized for mixed-signal processing instead of general purpose digital process in FPGA.
Development complexity and costs of integrated circuit is enormous. ASIC with same functionality as FPGA would be cheaper, but chips needs to be produced in large scale to be profitable. That's why there is relatively low number of DAC / ADC chip manufacturers.
FPGA is some kind of workaround for niche markets. But especially in mixed-signal FPGA is more expensive and slightly lower performance because of foundry process limitations.
Another thing, that I highly doubt that small manufacturer with low budget can design FPGA which can compete with state of the art DAC chips.
Digital DSP is slightly different situation, this is perfect application for FPGA chips.

 

[ZolaIII]

Hi,

Surprised, this thread hasn't more comments.

Especially since it is now 4 years old. Does it mean that no one is interested in those FGPA products ?

As far as I can see, it seems that FPGA can be used alongside a DAC chip like AKM or ESS or can be used as standalone solutions with no "DAC chips"..

Am I wrong assuming that the price or mastering the FPGA "concept" has lowered ?

Are there any drawbacks today in getting a FPGA based converter ? I mean : are the changes to get a poorly designed/engineered device higher than to get a porrly designed/engineered DAC ?

Please : do not reply saying "You can get a cheap DAC so grab one of those". I want something looking as I see fit... No too pricey, but not the cheapest. I am ready to go for that up-price but do not want to do anything wrong.

Regards.

FPGA is flexible programmable gate area.
Gate is a I/O aka transistor.
The more programmable gates larger the area to fit/test the design.
Anything that can fit the gate area can be programed to it.

FPGA's are mostly used & best suited for prototyping and squishing the final design bugs out. You can fit an actual DAC, CPU, GPU, ASIC, AI accelerator or anything else.
The biggest problem with FPGA's is a need for a very fast all direction interconnect between programmable cells (gates) in order to maintain interconnect coherence as much as possible. Of course this is very hard thing to do & so is programing them (choosing interconnect path).
All do there whose a lot of talk how their is a need for the flexible multi purpose reprogramable accelerators in order to put a stop to growing burden of black silicon (ASIC's switches special (single) purpose accelerators) which tends to pile up & eat growing part of final silicone. FPGA's as most flexible are most talked in that manner but they are to expensive for the user space. Development vent on & it's on going. So we got integrated self stand FPGA's with; general purpose CPU core's, memory sub systems, fast ASIC switches DSP's & cetera. For instance Altera (Intel) eFPGA's.
On the other hand DSP's also went trogh evolution process, gaining on function programmability and reprogram abilities (on math function lv), scalling, while remaining much cheaper & best suited for consumer space. For instance Tensilica Vision line.

In the end we will see what further brings & what ever it will be it will be designed on FPGA.

 

[audio2design]

For the less technical not sure it is obvious that the FPGA is just one part of the solution in a DAC doing typically high speed math beyond what is possible in a practical processor so that high sample rate high tap number filters can be implemented. FPGAs excel at this with potential for high levels of parallelism. Sure you could probably do it in a GPU at 25x the power draw and higher complexity.


You still need to bolt on analog to turn the FPGA into a DAC. That analog is integrated into an ESS DAC. There are mixed signal FPGAs but they are not suited to precision analog.


As die geometries shrink, mask costs go through the roof. Unless you build in very high volume and higher complexity, you can't justify an ASIC on an advanced process or even a few generations old in many cases. That is why FPGAs have moved into high volume applications 100K units and greater and why people will pay $1000+ for lower volumes. It's still way cheaper than an ASIC.

 

[PenguinMusic]

Hi,

Many many thanks for your answers.

Not sure I understood everything, but I think I got the whole picture

As far as I am concerned, I recently acquired the Aune x5s 6th (a small dedicated music player) and the Aune x7s (headphone amplifier).
The latter has been tested here and, htough not the best, it had more than decent results and so did other products from the same brand.

To get a complete system, I was considering the Aune x8.
They claim to have it running FGPA.
I must say that it is unclear if it also has a ASIC (from what I understood) or if the whole process relies on FPGA.
BUT from what I can see, there is no mention of any ESS or AKM chip no where to be seen on the product's description.

But when you say that a FGPA will not be as good as a ASIC DAC, will that difference be audible or be beyond hearing threshold ?

I know I can probably get another better device for the same price, but I like the size and looks and it will match in with the other 2 I mentioned.
So I am ready to pay a premium for that... but would not like to do anything wrong and have something that sound really really poor :-(
And it has been stated elsewhere that, as soon as a DAC is properly designed and engineered, differences can be measured but aren't audible.

As I am not skilled enough to understand their own measurements that are published on their webpage I was wondering if those can be considered as getting to the threshold where the difference is audible or not...

If someone would have infos/thoughts on that, I'd be grateful.

Regards.

 

[ZolaIII]

@PenguinMusic uffff I really don't know what to say. Word magic sounding simply appears to often regarding it. The DAC used for USB line is Sabre ES9038 (probably QM2 - dual channel striped down variant for mobile devices). I am sceptic about measurements presented on their page as SINAD of 106 dB is to close to DAC specification of 107 dB. If true that's perfectly enough even with great headphones. I do understand your sentiment and that you want a set to visually pair it but you know you can get better for the money. It seams good engineered having coaxial, optical and usb inputs, separate power line and cetera.
I probably wouldn't buy it ever for all the snake oil stories surrounding it but anyway that's me.

FPGA is more of a EPP than anything else. Sure it does have a small "self developed" one which does resampling and me by something else like on Mojo (basically DSP job) but that's about it.

You didn't actually understand the talk about FPGA's but never mind. Best regards.

 

[PenguinMusic]

Hi Zolalll,

Thanks a lot for your answer.

I should have mentioned that I don't care about the "Magic" word. Cambridge audio also had "Magic DAC's" and I found them magically horrible !

I am not looking for a FPGA DAC just for fun.
Quite the opposite !

From what I understood about FPGA :
- is flexible when developping ;
- is difficult to master ;
- is quite expensive for large quantities, but in small quantities, much cheaper than producing ASIC's ;
- can be used for the whole DAC chain or can be used in conjunction with ASIC (ESS or AKM).

Is that correct or am I really totally not getting it ? My ego has already suffered a lot in here, so you can tell me honestly

If that is correct, from what you wrote, it seems that the Aune X8 is not "pure FPGA" but relies on ESS 9038 for the DAC part.
I've seent the 9038 mentioned nowhere, but if that is sure, that is quite reassuring for me.

As I already said, I know I can probably get something that MEASURES better.
But if the difference is barely audible, if audible at all, I'm ready to spend that extra on the looks alone...

Yes, irrational I know and I apologize for that...

Regards.

 

[Katji]

It's not only your ego that is suffering here.

 

[audio2design]

From what I understood about FPGA :
- is flexible when developping ;
- is difficult to master ;
- is quite expensive for large quantities, but in small quantities, much cheaper than producing ASIC's ;
- can be used for the whole DAC chain or can be used in conjunction with ASIC (ESS or AKM).

Think about an FPGA as a fancy microprocessor, like the one in your computer. It is not a DAC. When used in conjunction with external analog circuitry, it can form a DAC function. Modern DACs are a combination of digital interface logic (to receive digital data), digital signal processing, digital logic in combination with analog circuitry for primary DAC functions (could be 1 bit or many bits), and then finally analog filtering.


The FPGA can perform all those digital functions of a modern DAC chip (ASIC), but almost as a rule, don't have the required analog functionality. There are some FPGA with analog functions, but they are not targeted at high resolution, low noise like high end audio.


Yes, you could use an FPGA with simple external analog functions, or you could use an FPGA to provide interface logic and advanced digital signal processing and then connect that to a DAC IC.

 

[ZolaIII]

@PenguinMusic of course it's not a FPGA only. They used 3$ DAC IC and a 1$ OP amp (one of two actually). Why they used an FPGA instead of DSP is something only they know. Probably they warent satisfied with something, who knows. The ES9038 is mentioned probably everywhere else expect on their own site, on some places as ES9038Q2M which while I can not confirm I think it's true. They perform the same while later is 2 channels instead of 8. OP Amp's are exchangeable (not that you will change them).

Easiest way to understand what FPGA is is to imagine it as empty sheet of paper, one of those with little squares that we all used for math. Every square represents a gate & it literally becomes what you draw on it. Then you can use eraser to change re draw part of it or all of it.

You won't hear a difference over 100 dB SINAD for sure but how ever there are some other advantages with let's say use of balanced out which you even could hear like better separation and the fact you won't ever have a problem with ground loops or using long cables among the things i can remember right now.

In the end its all about what you need & every need has an ego to feed.

 

[PenguinMusic]

It's not only your ego that is suffering here.

Don't know waht you mean, but OK...

Regards.

 

[PenguinMusic]

Think about an FPGA as a fancy microprocessor, like the one in your computer. It is not a DAC. When used in conjunction with external analog circuitry, it can form a DAC function. Modern DACs are a combination of digital interface logic (to receive digital data), digital signal processing, digital logic in combination with analog circuitry for primary DAC functions (could be 1 bit or many bits), and then finally analog filtering.


The FPGA can perform all those digital functions of a modern DAC chip (ASIC), but almost as a rule, don't have the required analog functionality. There are some FPGA with analog functions, but they are not targeted at high resolution, low noise like high end audio.


Yes, you could use an FPGA with simple external analog functions, or you could use an FPGA to provide interface logic and advanced digital signal processing and then connect that to a DAC IC.

Hi,

OK. That is somewhat more clear to me now.

Thanks a lot for taking time to explain

 

[PenguinMusic]

@PenguinMusic of course it's not a FPGA only. They used 3$ DAC IC and a 1$ OP amp (one of two actually). Why they used an FPGA instead of DSP is something only they know. Probably they warent satisfied with something, who knows. The ES9038 is mentioned probably everywhere else expect on their own site, on some places as ES9038Q2M which while I can not confirm I think it's true. They perform the same while later is 2 channels instead of 8. OP Amp's are exchangeable (not that you will change them).

Easiest way to understand what FPGA is is to imagine it as empty sheet of paper, one of those with little squares that we all used for math. Every square represents a gate & it literally becomes what you draw on it. Then you can use eraser to change re draw part of it or all of it.

You won't hear a difference over 100 dB SINAD for sure but how ever there are some other advantages with let's say use of balanced out which you even could hear like better separation and the fact you won't ever have a problem with ground loops or using long cables among the things i can remember right now.

In the end its all about what you need & every need has an ego to feed.

Hi,

Thanks a lot for taking time to reply to me.

I think I begin to get to understand a little more about FPGA's.
Quick question : if it is like those little squares, can it be that a "serious" manufacturer can update it's product (an make that update available to you & me) with a "firmware" update ?

Now, back to the subject : as I hear you, the x8 may not be bad, but you would serioulsy consider something else for the price.
Something that would measure (much) better but will only marginally sound better, if it sounds different at all. And with features like, maybe, balanced.
Personnally, I do have no plans on using long runs of cable so I probably do not need balanced and, the common saying on another thread is that the extra power in balanced would not be need given the used headphones (Oppo PM-1 : 32 Ohm and 102dB).

But of course, if you can advise something that looks good, has about the same price (up to 250/300 dollars) and that has stellar measurements, I may consider your advice (provided the device is available easily in Europe/France).

Thanks again for taking time to reply

 

[audio2design]

Most FPGAs can be updated just like you would update the software on your computer. The limitation will always be the external analog circuity.

 

[RayDunzl]

What about Chord?

TL;DW

 

[PenguinMusic]

What about Chord?

TL;DW

Hum,

From what I hear, Chord sometimes produces really good devices, with stellar measures. And sometimes devices that measure really poorly.

In every case, they charge a HUGE premium to get to their devices.

And those are simply out of my league... And on another thread (in which you participated I think) the common rule was : "Beyond a specific threshold, difference is measurable but not audible, so choose according to budget, aesthetics and features but not on sound "signature" (does that ring a bell about the thread I'm referring to ?)

Besides their price, I find the Chord devices to be too far from my own tastes...

 

[PenguinMusic]

Most FPGAs can be updated just like you would update the software on your computer. The limitation will always be the external analog circuity.

Of course, if the manufacturer is kind enough to privde updated files

I think we should not depend on that as they probably won't support that :-(

 

[RayDunzl]

Hum

Yeah, just mentioning Chord as an example of someone using FPGA and no "DAC" chip (from what little I can gather)

 

[PenguinMusic]

Yeah, just mentioning Chord as an example of someone using FPGA and no "DAC" chip (from what little I can gather)

Hi,

Oh... OK. Sorry.

Not sure, but I think Amir said they do not use an "off the shelve DAC". Which may mean that they do not use ASIC at all... or that they have made their own. But the latter seems difficult to think of if I consider what has been written above about the price for such development !

Regards.

 

[audio2design]

At 3:02 in the Chord presentation, you will find a lie where they claim that there technology is necessary for timing accuracy which is not true. All they can claim is oversampling to push the frequency up and reduce changes in phase due to analog filtering. Their claims to improved accuracy only hold water if you ignore analog post filtering. They claim huge numbers of taps, which is good, but ignore the real "processing" that occurs post DAC in the analog domain.