Quote from: Clemmaster on October 01, 2014, 10:18:23 PM

Quote from: purr1n on October 01, 2014, 09:49:46 PM

Well, would you use one of these DACs for audio?



Do you want to be up to 15 LSBs off? Which for 16 bits, means 4 bits off? So how would you like to 3 to 4 bits louder than you are supposed to be from 0.20V to 0.40V on a 2V output DAC?

How do you get 0.2 to 0.4V?

15 LSBs for a 16bits / 2V DAC is more like 0.00091V (0.046%)?

Look at region from slight past 32768 (0 volt) to 40960 (0.5 volt) - assuming +/-2V peak. Get it now? 10 to 15 LSBs off (higher) between that point. 2^3 = 8. 2^4 = 16.

Oh, I thought you meant 3-4 bits off was like 0.2 to 0.4V off a 2V scale. I was scared for a bit

Also, your sinewave won't be 3-4 bits louder. Again, this is a static measurement. Your sinewave is made of many word codes (each with their own error).
It will for sure result in a distorted sine wave and it would be interesting to do a simulation and get the classic THD and SNR out of it.

You are right. Sine wave don't get louder given the randomness of nature and how it evens out. But parts of the sine wave will be louder, and parts softer. Yup. Think of the curved lines of the sine wave being all crooked and shit. Lack of relative accuracy = distortion. Hmmm. Makes me wonder about a measurement of a specific DAC where there was a lot of high frequency hash on the distortion measurement.

May or may not be related (as you can tell, I'm pretty uneducated in this area), but one of these DACs with these supposed chips did have some interesting measurement results from an unorthodox test. With a 1-minute sample of some 16/44.1 music, measured and averaged in ARTA (exp mode) and zoomed in to show small differences, there were noticeable variations with the three test results. When upsampled to 24/176.4 via playback software, the results matched much more closely. Almost identical. Related or not, or what that would mean in the end exactly, I'm not sure. (Would have to run tests on other DACs to see how they handle this weird test - thought this was done, but can't find evidence of it here...faulty memory, perhaps.) Again, not an expert, so apologies if this is dumb.

So, going back to the LSB errors, it is interesting to speculate and test A) how that might affect other, more commonly used DAC measurements and B) how that might affect what we hear subjectively in the end.

It's Typical Chart, so proly one sample chip. Not sure if it would be a median though.

LOL, that's a 3 MSPS DAC.

http://www.ti.com/lit/ds/symlink/dac8581.pdf

BTW: One thing that maybe done is to set the delta sigma to fixed DC codes and get points out of it. But that will include not just the IC, but the entire solution and it could be a little time consuming (2^24 codes! ... and forget about 32 bits). One would have to wait for the DS to settle. Maybe one could do jump multiple steps? Not sure about automation.

Ha, say we take a DC value 1 second and a time... We will be done in 6.5 months. 70 years for a 32 bit DAC. Would have to skip or take samples quite a bit faster. But again, that would require some automation. Maybe play a stair case deal. Dunno how long to wait for the settling time. Will think.

EDIT: Forget it. Delta Sigma has memory and outputs will depend on previous inputs. That means that if we did the stair case deal, we would likely be off still. Thats because if we tried a different random stair case or indeed any other signal, we might get completely different results. LOL! Guess that explains why we didn't get those INL/DNL specs from the analog dudes, and worked of the ENOB and SINAD... I did also work on some digital delta sigma stuffs, but did not have to deal with this INL/DNL crap. We were more concerned with ppm jitter which I guess is kind of related. The part that made it easier is that we only had to be concerned with certain discrete codes.

Well, would you use one of these DACs for audio?



Do you want to be up to 15 LSBs off? Which for 16 bits, means 4 bits off? So how would you like to 3 to 4 bits louder than you are supposed to be from 0.20V to 0.40V on a 2V output DAC?

I have a completely different view than you have.
Here it goes:
1LSB = 1/65536 x 5.657V (for a 2Vrms out DAC) = 0.086mV
The DAC can be off +/- 15 bits
This is due to tolerances of the MSB, 2SB and 3SB which needs an extremely small tolerance because of the LSB.
So the DAc can be 'off' 15x the 'size' of 0.086mV = 1.29mV (which still is a LOT) in an absolute sense.
so a 2V_RMS sinewave may be 'off' 0.9mV_RMS around the '0V' line (-67dB).
It looks like 'crossover' distortion.