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Author Topic: DAC guts stuff, etc.  (Read 11920 times)

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Clemmaster

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Re: DAC guts stuff, etc.
« Reply #20 on: October 01, 2014, 10:05:29 PM »

At least the differential error is low, which means that my sinewave would keep a nice shape and not distort like crazy. That's another way to look into it.
Isn't a 4bit error below the variation between 2 headphones anyway?

You could well design a DAC that has very low linearity error, which would be good for static measurement (voltmeters and all) but would it be able to keep these good measurement with a 10kHz sinewave?

I briefly looked at the datasheet of the super accurate DAC you posted yesterday and could never find any mention of actual sample rate.
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Marvey

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Re: DAC guts stuff, etc.
« Reply #21 on: October 01, 2014, 10:09:04 PM »

Honestly, I don't think it would be that bad. Maybe the guys at Schiit would differ. :-)

One way to test is to take that graph and make an error function. And then apply to the raw WAVE file. For every word (16bit), fuck up the value a little bit according to the function. And then see how it sounds.

In terms of SD, you are probably right it doesn't apply since error will be different. But what happens (subjectively) to the WAVE file when we feed it into a DAC and add random noise per X sample after conversion of PCM to single or multi-bit?

Again, all conjecture.
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Marvey

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Re: DAC guts stuff, etc.
« Reply #22 on: October 01, 2014, 10:12:02 PM »

I could tell the measurement wasn't good based on your comments, haha, just wasn't sure what I was looking at. OK, so 15 LSBs would be 4 bits off for 16 bit. Stuff like that is what I was asking if you had recommended reading for. Looking around myself as well to get myself educated, just wondered if you stumbled on anything easy to understand or digest. (Admittedly, this bit-level stuff, especially dealing with LSBs or MSBs went mostly over my head in that class, but maybe something is still stuck in my brain.)

x x x x x x x x x x x x x x x x (16 bits)

MSB                                     LSB
 
2^15  2^14   .........  2^2  2^1  1


using signed short 16-bit:

-32768 or 8000 (hex) = -2 volts
0 (dec) or 0000 (hex) = 0 volts
32768 or 7FFF (hex) = 2 volts

shift everything over (add 32768) and the graph should make sense.
or something like that. you get the idea.
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Clemmaster

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Re: DAC guts stuff, etc.
« Reply #23 on: October 01, 2014, 10:15:07 PM »

Honestly, I don't think it would be that bad. Maybe the guys at Schiit would differ. :-)

One way to test is to take that graph and make an error function. And then apply to the raw WAVE file. For every word (16bit), fuck up the value a little bit according to the function. And then see how it sounds.

In terms of SD, you are probably right it doesn't apply since error will be different. But what happens (subjectively) to the WAVE file when we feed it into a DAC and add random noise per X sample after conversion of PCM to single or multi-bit?

Again, all conjecture.

I could do that from the LE graph with Matlab. Alas, I only have Scilab at work and it is VERY poor with image processing (to build the mapping function) :/

You reminded me what I wanted to try today :D
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Clemmaster

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Re: DAC guts stuff, etc.
« Reply #24 on: October 01, 2014, 10:18:23 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%)?
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Hands

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Re: DAC guts stuff, etc.
« Reply #25 on: October 01, 2014, 10:19:41 PM »


[size=78%]x x x x x x x x x x x x x x x x (16 bits)[/size]


MSB                                     LSB
 
2^15  2^14   .........  2^2  2^1  1


Ah, yep. Got it!  :)p5
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ultrabike

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Re: DAC guts stuff, etc.
« Reply #26 on: October 01, 2014, 10:20:59 PM »

Marv, if you have the Wav files sent them to me.

One thing though. Use the highest sampling rate you can from your ADC. If its 96 kHz, use that. Also use the highest resolution supported, and if you can use ASIO drivers. Make sure you are using full resolution or somehow have some reference (i.e. try to fully load the DAC).
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Marvey

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Re: DAC guts stuff, etc.
« Reply #27 on: October 01, 2014, 10:23:05 PM »

LOL, can you just convert one of your songs to WAV?
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ultrabike

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Re: DAC guts stuff, etc.
« Reply #28 on: October 01, 2014, 10:23:53 PM »

Yup. But don't have R-2R goodness.

Can try with whatever I have.
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Marvey

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Re: DAC guts stuff, etc.
« Reply #29 on: October 01, 2014, 10:25:16 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.
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