dac noob is confused - Page 1
Forum section: electronics / projects

author: sahko123
author_rank: Frequent Contributor
timestamp: March 02, 2019, 10:34:27 pm
content: 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

author: Wimberleytech
author_rank: Super Contributor
timestamp: March 02, 2019, 10:38:01 pm
content: There are usb-i2c modules, there are usb-serial chips and modules...beyond that you need to tell us more.

author: sahko123
author_rank: Frequent Contributor
timestamp: March 02, 2019, 10:45:23 pm
content: 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)

author: Wimberleytech
author_rank: Super Contributor
timestamp: March 02, 2019, 10:56:47 pm
content: 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?"

author: Wimberleytech
author_rank: Super Contributor
timestamp: March 02, 2019, 10:58:03 pm
content: ...and what, pray tell, is a 32bit DAC? It does not exist...pretty sure.

author: sahko123
author_rank: Frequent Contributor
timestamp: March 02, 2019, 11:02:36 pm
content: https://www.digikey.ie/product-detail/en/akm-semiconductor-inc/AK4493EQ/974-1162-ND/8124021AK4493EQ 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 useand 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

author: Wimberleytech
author_rank: Super Contributor
timestamp: March 02, 2019, 11:27:56 pm
content: 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.

author: sahko123
author_rank: Frequent Contributor
timestamp: March 02, 2019, 11:35:07 pm
content: if it calls itself 32bit but is actually 20 odd bit why does it accept(supposedly) a 32bit input

author: sahko123
author_rank: Frequent Contributor
timestamp: March 02, 2019, 11:54:32 pm
content: 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

author: radiolistener
author_rank: Super Contributor
timestamp: March 03, 2019, 12:19:18 am
content: Quote from: Wimberleytech on March 02, 2019, 10:58:03 pmit 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 quadroyes, 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

author: Wimberleytech
author_rank: Super Contributor
timestamp: March 03, 2019, 12:35:46 am
content: Quote from: radiolistener on March 03, 2019, 12:19:18 amHell, 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."

author: radiolistener
author_rank: Super Contributor
timestamp: March 03, 2019, 12:49:35 am
content: Quote from: Wimberleytech on March 03, 2019, 12:35:46 amno, 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.

author: Wimberleytech
author_rank: Super Contributor
timestamp: March 03, 2019, 01:01:05 am
content: Quote from: radiolistener on March 03, 2019, 12:49:35 amCome 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.

author: radiolistener
author_rank: Super Contributor
timestamp: March 03, 2019, 01:13:50 am
content: Quote from: Wimberleytech on March 03, 2019, 01:01:05 amAK4499 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?Quote from: Wimberleytech on March 03, 2019, 01:01:05 ambut 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.

author: SiliconWizard
author_rank: Super Contributor
timestamp: March 03, 2019, 01:15:18 am
content: 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.

author: Wimberleytech
author_rank: Super Contributor
timestamp: March 03, 2019, 01:40:06 am
content: Quote from: SiliconWizard on March 03, 2019, 01:15:18 amOK, 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?

author: radiolistener
author_rank: Super Contributor
timestamp: March 03, 2019, 01:46:57 am
content: yes, delta-sigma technology allows to improve linearity, it allows to get much better SNR performance than with classic DAC.

author: Wimberleytech
author_rank: Super Contributor
timestamp: March 03, 2019, 01:59:06 am
content: Quote from: radiolistener on March 03, 2019, 01:46:57 amCertainly!...but that is not where this discussion started.

author: radiolistener
author_rank: Super Contributor
timestamp: March 03, 2019, 02:05:14 am
content: Quote from: Wimberleytech on March 03, 2019, 01:40:06 amThere 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 worldReal 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

author: Wimberleytech
author_rank: Super Contributor
timestamp: March 03, 2019, 02:26:37 am
content: Quote from: radiolistener on March 03, 2019, 02:05:14 amYes, 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.

author: radiolistener
author_rank: Super Contributor
timestamp: March 03, 2019, 02:54:40 am
content: Quote from: Wimberleytech on March 03, 2019, 02:26:37 amthere 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 realHere is spectrum of AK4499 output from their presentation:

author: SiliconWizard
author_rank: Super Contributor
timestamp: March 03, 2019, 02:57:10 am
content: 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

author: Wimberleytech
author_rank: Super Contributor
timestamp: March 03, 2019, 03:09:56 am
content: Quote from: radiolistener on March 03, 2019, 02:54:40 amThis is not 32bits. I give up.

author: jmelson
author_rank: Super Contributor
timestamp: March 03, 2019, 03:15:04 am
content: Quote from: sahko123 on March 02, 2019, 10:34:27 pmSorry 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

author: jmelson
author_rank: Super Contributor
timestamp: March 03, 2019, 03:16:44 am
content: Quote from: Wimberleytech on March 02, 2019, 10:58:03 pmYup, I think the 32-bits refers to a "frame" which contains two 16-bit samples, one left-channel, ore right.Jon

author: radiolistener
author_rank: Super Contributor
timestamp: March 03, 2019, 04:03:16 am
content: Quote from: jmelson on March 03, 2019, 03:15:04 am1 V is too small, it's better to use higher voltage, because it's hard to deal with nanovolt level noise.For example 9 V, as used in AK4499 DAC.Human ear dynamic range is about 140 dB.Unfortunately existing 24 bit DAC cannot provide so high dynamic range with no distortions and noises.This is the reason for 32 bit DAC...Quote from: jmelson on March 03, 2019, 03:16:44 amNo, it refers to 32 bit word for single channel (mono) and all 32 bits are meaning.AK4499 can works with up to 4 channels (mono, stereo and quadro) with each channel 32 bit resolution.But the best 32 bit sound with SNR=140 dB is avaliable for single channel mode (mono) only.In stereo mode it also uses 32 bit resolution, but SNR=137 dB.

author: sahko123
author_rank: Frequent Contributor
timestamp: March 03, 2019, 10:28:33 am
content: along with the dynamic range of 140db which for audio is about all nobody will ever need(except for those who are interested in getting the best most realistic audio perfomance(realism means dynamics reality isnet compressed)) and "32" bit performance means that high frequencies can be along with the high samping rate of 768khz can be represented more closer to an analog signal with lower top end distortion which is the biggest problem in lower quality(resolution) dacsalso im not looking for ideal 32bit performance(unless it was possible, but probably overkill) i doesnt bother me that its not actually 32bit it still has tangible performance benefits over other dacs over lower bit width.also thanks SiliconWizard for the xmos board ill be sure to check it out further