Author Topic: dac noob is confused  (Read 4751 times)

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Offline sahko123Topic starter

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dac noob is confused
« on: March 02, 2019, 10:34:27 pm »
im interested in adding a 32bit 768khz dac into an integrated amp design but have no clue how to turn the usb input into an I2C or I2S is this generally done with a microprocessor or dsp or what? NOt looking for recomendations (though they will be helpful) just some search terms to get me going
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Offline Wimberleytech

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Re: dac noob is confused
« Reply #1 on: March 02, 2019, 10:38:01 pm »
There are usb-i2c modules, there are usb-serial chips and modules...beyond that you need to tell us more.
 

Offline sahko123Topic starter

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Re: dac noob is confused
« Reply #2 on: March 02, 2019, 10:45:23 pm »
is it really that simple?(with a usb to serial converter) because i thought there would have to be  some processing before hand and when it comes to driving the usb signal you would need drivers. i wasnt sure if regular usb to serial processors could handle the 32bit 768khz the way i need them to(with low signal jitter output and precise data timing)
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Offline Wimberleytech

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Re: dac noob is confused
« Reply #3 on: March 02, 2019, 10:56:47 pm »
No it is not that simple.  Are you controlling your amp using a PC?  You need drivers, etc.  But like I said we need more information...your question is like "which way do I turn when I get to the intersection?"
 

Offline Wimberleytech

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Re: dac noob is confused
« Reply #4 on: March 02, 2019, 10:58:03 pm »
...and what, pray tell, is a 32bit DAC?  It does not exist...pretty sure.
 

Offline sahko123Topic starter

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Re: dac noob is confused
« Reply #5 on: March 02, 2019, 11:02:36 pm »
https://www.digikey.ie/product-detail/en/akm-semiconductor-inc/AK4493EQ/974-1162-ND/8124021 


AK4493EQ is my dac of choice. my dilemma is i have no clue how to get from a pc usb output into the I2C input of the DAC or if theres antoher input format that is better to use

and when it comes to ''controlling your amp with a pc'' all im doing is converting usb in to audio out and the rest is analog circuitry

« Last Edit: March 02, 2019, 11:10:23 pm by sahko123 »
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Offline Wimberleytech

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Re: dac noob is confused
« Reply #6 on: March 02, 2019, 11:27:56 pm »
OK, AKM calls it a 32bit DAC...but it has 120dB SNR which is 20bit performance.  I see it touts 32bit digital filters...that is where the 32 comes from.
 

Offline sahko123Topic starter

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Re: dac noob is confused
« Reply #7 on: March 02, 2019, 11:35:07 pm »
if it calls itself 32bit but is actually 20 odd bit why does it accept(supposedly) a 32bit input
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Offline sahko123Topic starter

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Re: dac noob is confused
« Reply #8 on: March 02, 2019, 11:54:32 pm »
so essentially a "32"bit DAC is used to prevent data fuckery when being connected to a 32bit data source(audio file) and DSP. so i assume the same data problems can be prevented if 24bit data source went into a 24bit dsp and a "24"bit dac, with liitle to no quality difference if the effective bit width is 20 or so bits
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Offline radiolistener

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Re: dac noob is confused
« Reply #9 on: March 03, 2019, 12:19:18 am »
...and what, pray tell, is a 32bit DAC?  It does not exist...pretty sure.

it exists, for example AK4499. According to the datasheet it has 32 bit and has:
- SNR 140 dB for mono
- SNR 137 dB for stereo
- SNR 134 dB for quadro

yes, I know that SNR=140 dB is corresponds to 23-bit ideal DAC, but we're talking about real DAC, it's a bit worse than ideal :)
« Last Edit: March 03, 2019, 12:26:11 am by radiolistener »
 

Offline Wimberleytech

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Re: dac noob is confused
« Reply #10 on: March 03, 2019, 12:35:46 am »
...and what, pray tell, is a 32bit DAC?  It does not exist...pretty sure.

it exists, for example AK4499. According to the datasheet it has 32 bit and has:
- SNR 140 dB for mono
- SNR 137 dB for stereo
- SNR 134 dB for quadro

yes, I know that SNR=140 dB is corresponds to 23-bit ideal DAC, but we're talking about real DAC, it's a bit worse than ideal :)

Hell, you can call it 64bit if you want but nothing can resolve 64bits or 32bits for that matter (dunno, maybe at 0K you can, but that is damn cold).  These are "marketing bits."
 

Offline radiolistener

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Re: dac noob is confused
« Reply #11 on: March 03, 2019, 12:49:35 am »
Hell, you can call it 64bit if you want but nothing can resolve 64bits or 32bits for that matter (dunno, maybe at 0K you can, but that is damn cold).  These are "marketing bits."

no, I don't think this is marketing. Any ADC or DAC has ENOB lower than it's bit width.
This is because ENOB and SNR depends on jitter, linearity, noise and many other things.
Which for real ADC/DAC will never be the same as for theoretical ideal ADC/DAC.
Real DAC/ADC always will be a little worse than theoretical ideal DAC/ADC.
For real DAC/ADC there always will be some jitter, non-linearity, noise and other stuff, which will leads to SNR degradation.
But these bits are fair.

Just check, you will not be able to get SNR=140 dB on any of existing 24 bit DAC.
But this 32 bit DAC provides SNR=140 dB.
« Last Edit: March 03, 2019, 12:57:16 am by radiolistener »
 

Offline Wimberleytech

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Re: dac noob is confused
« Reply #12 on: March 03, 2019, 01:01:05 am »
Hell, you can call it 64bit if you want but nothing can resolve 64bits or 32bits for that matter (dunno, maybe at 0K you can, but that is damn cold).  These are "marketing bits."

no, I don't think this is marketing. Any ADC or DAC has ENOB lower than it's bit width.
This is because ENOB and SNR depends on jitter, linearity, noise and many other things.
Which for real ADC/DAC will never be the same as for theoretical ideal ADC/DAC.
Real DAC/ADC always will be a little worse than theoretical ideal DAC/ADC.
For real DAC/ADC there always will be some jitter, non-linearity, noise and other stuff, which will leads to SNR degradation.
But these bits are fair.

Come on...32bits is meaningless.  At least 8 bits are noise (and that is being kind to the DAC).

Lets say you have a 5V reference.  The LSB is about a nanovolt. 

I can design you a DAC that has 32bit input but you will never get 32bit performance.  The fact that there are 32 digital bit at the input means nothing.


 

Offline radiolistener

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Re: dac noob is confused
« Reply #13 on: March 03, 2019, 01:13:50 am »
Lets say you have a 5V reference.  The LSB is about a nanovolt. 

AK4499 uses 9V reference and it's noise is about 1 uV.
It means SNR = 1/9000000 = 139 dB.
Which is close to the datasheet value SNR=140 dB.
So, it looks fair. What is wrong here?

I can design you a DAC that has 32bit input but you will never get 32bit performance.

but this DAC is designed as 32 bit and has 32 bit performance.
Yes, it is not good enough like theoretical model of ideal 32-bit DAC (which doesn't exists in reality), but it works good and gives performance much better than 24 bit DAC.
« Last Edit: March 03, 2019, 01:20:40 am by radiolistener »
 

Online SiliconWizard

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Re: dac noob is confused
« Reply #14 on: March 03, 2019, 01:15:18 am »
Note that a sigma-delta DAC can be implemented with pretty much any bit width - it's a very scalable and 100% digital (except the analog front-end obviously) topology. You can make a 64-bit DAC for that matter, it's just pretty much a matter of silicon area and max clock frequency.

You will always get a lower ENOB than the DAC bit width, but increasing the bit width is a pretty simple way of increasing the ENOB without having to resort to overly complex digital filtering, which is not only tricky but can also take a lot more area (more transistors) than barely increasing the bit width and using much simpler digital filtering. Thus it may be a way of actually getting a given performance level with reduced power consumption for instance.

Marketing a 32-bit sigma-delta DAC as 32-bit is indeed kind of misleading as it's mainly a technical choice and certainly doesn't have 8 more ENOBs than good 24-bit sigma-delta DACs, but it's not a lie per se.
 

Offline Wimberleytech

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Re: dac noob is confused
« Reply #15 on: March 03, 2019, 01:40:06 am »

Marketing a 32-bit sigma-delta DAC as 32-bit is indeed kind of misleading as it's mainly a technical choice and certainly doesn't have 8 more ENOBs than good 24-bit sigma-delta DACs, but it's not a lie per se.

OK, we agree (kinda).  Marketing is not lying...it is, well, marketing!

BTW, I understand how delta-sigma DAC (and ADCs) work.

You say "analog front-end" when I think you mean back-end smoothing filter (for a DAC), no?
 

Offline radiolistener

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Re: dac noob is confused
« Reply #16 on: March 03, 2019, 01:46:57 am »
yes, delta-sigma technology allows to improve linearity, it allows to get much better SNR performance than with classic DAC.

 

Offline Wimberleytech

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Re: dac noob is confused
« Reply #17 on: March 03, 2019, 01:59:06 am »
yes, delta-sigma technology allows to improve linearity, it allows to get much better SNR performance than with classic DAC.

Certainly!...but that is not where this discussion started.
 

Offline radiolistener

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Re: dac noob is confused
« Reply #18 on: March 03, 2019, 02:05:14 am »
Marketing is not lying...it is, well, marketing!

There is no marketing. You're trying to compare parameters of real DAC with parameters of ideal DAC.
Ideal DAC is just a theoretical model, it will never be created, because this is DAC which bypass all known physical limitations and impossible to implement in the real world :)

Real DAC parameters always will be worse.
It has non ideal linearity, non-zero jitter, some real world noises.
And this is why it's SNR is worse. Not because marketing or fake bit resolution  :)
 

Offline Wimberleytech

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Re: dac noob is confused
« Reply #19 on: March 03, 2019, 02:26:37 am »
Marketing is not lying...it is, well, marketing!

There is no marketing. You're trying to compare parameters of real DAC with parameters of ideal DAC.
Ideal DAC is just a theoretical model, it will never be created, because this is DAC which bypass all known physical limitations and impossible to implement in the real world :)

Real DAC parameters always will be worse.
It has non ideal linearity, non-zero jitter, some real world noises.
And this is why it's SNR is worse. Not because marketing or fake bit resolution  :)

Yes, and I do real magic.  Forget the fact that it is illusion...that is just a manifestation of the real world in which we live.  Trust me, I made that helicopter disappear before your eyes.
 

Offline radiolistener

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Re: dac noob is confused
« Reply #20 on: March 03, 2019, 02:54:40 am »
Yes, and I do real magic.  Forget the fact that it is illusion...that is just a manifestation of the real world in which we live.  Trust me, I made that helicopter disappear before your eyes.

there is no magic, all resolution bits of this DAC are meaning, nothing cut, nothing disappears. SNR and ENOB of ideal DAC is used just for indication of theoretical limit for the specified resolution. Such limit will be never reached in the real world, because it's impossible.

So, if you see that SNR of your DAC is worse than SNR of ideal DAC with the same resolution, this is normal. There is nothing wrong, and it's resolution is not fake, it's real :)

Here is spectrum of AK4499 output from their presentation:




 

Online SiliconWizard

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Re: dac noob is confused
« Reply #21 on: March 03, 2019, 02:57:10 am »
To answer the OP's question, there are controller boards you can use that will have USB connectivity and I2S output(s), and will be seen as an audio device on most OSs.

You can take a look at the XMOS-based boards for instance, such as this: https://www.diyinhk.com/shop/audio-kits/107-xmos-dsd-dxd-768khz-high-quality-usb-to-i2sdsd-pcb.html
 
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Offline Wimberleytech

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Re: dac noob is confused
« Reply #22 on: March 03, 2019, 03:09:56 am »
Yes, and I do real magic.  Forget the fact that it is illusion...that is just a manifestation of the real world in which we live.  Trust me, I made that helicopter disappear before your eyes.

there is no magic, all resolution bits of this DAC are meaning, nothing cut, nothing disappears. SNR and ENOB of ideal DAC is used just for indication of theoretical limit for the specified resolution. Such limit will be never reached in the real world, because it's impossible.

So, if you see that SNR of your DAC is worse than SNR of ideal DAC with the same resolution, this is normal. There is nothing wrong, and it's resolution is not fake, it's real :)


This is not 32bits.  I give up.
 

Online jmelson

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Re: dac noob is confused
« Reply #23 on: March 03, 2019, 03:15:04 am »
im interested in adding a 32bit 768khz dac into an integrated amp design but have no clue how to turn the usb input into an I2C or I2S is this generally done with a microprocessor or dsp or what? NOt looking for recomendations (though they will be helpful) just some search terms to get me going
Sorry to be crude, but only an idiot would buy a 32-bit DAC.  If the full-scale voltage is 1 V, then the value of a single bit is 1/4294967296 of that, or 2.33 x 10 ^ -10.  That's 23 NANO-volts!  What could you possibly build that could detect such small signals?
Can you build a reference voltage supply that has noise within 1000 times that?  And, then you are going to pipe that through an audio amp and speakers?

Jon
 
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Online jmelson

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Re: dac noob is confused
« Reply #24 on: March 03, 2019, 03:16:44 am »
...and what, pray tell, is a 32bit DAC?  It does not exist...pretty sure.
Yup, I think the 32-bits refers to a "frame" which contains two 16-bit samples, one left-channel, ore right.

Jon
 
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