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

Marvey · « **on:** September 30, 2014, 08:13:00 PM »

Just a had thought. Again, could be talking out of my ass. All conjecture. Could differences among the types of DACs, resistor ladder, 1-bit, multi-bit/hybrid, SABRE (who knows since no public documentation) be a result of the types of linearity errors.

For resistor ladder DACs, the linearity errors would be of a certain sort. Resistors trimmed slightly off. Like bit 4 output is 16.3 (instead of perfect 2^4=16) to 32768 from bit 15 output(assumming bit 15 output is perfect). No matter what, the bit 4 output is always going to be in slight error, and consistently of that slight error.

For sigma-delta, noise shaping would be used. This of course would introduce a entirely different type of linearity errors, but given how sigma-delta works, the overall error would be less. It would seem much more difficult to get the ladder DACs to be just as linear given the difficultly of precision trimming of the resistors.

Now how does this correlate to what we hear? Those of you who have heard enough DACs, quality DACs that is of both kinds, know that resistor ladder and sigma-delta sound different and have different strengths. The best sigma-delta implementations sound highly detailed with sharp attacks. The best resistor ladder DACs sound smooth with natural timbre.

Would in interesting to see some linearity plots (output vs. bitcode), DNL, and INL plots of both kinds. Maybe there is something. Maybe not.

Maybe greater linearity = more resolving (it's true mathematically, but is it true subjectively?) Maybe linearity error plots with certain more predictable patterns = smoother more natural sound?
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Added by Anaxilus for other considerations. All comments welcome.

ultrabike · « **Reply #1 on:** September 30, 2014, 09:05:16 PM »

Quote from: purr1n on September 30, 2014, 08:13:00 PM

Just a had thought. Again, could be talking out of my ass. All conjecture. Could differences among the types of DACs, resistor ladder, 1-bit, multi-bit/hybrid, SABRE (who knows since no public documentation) be a result of the types of linearity errors.

For resistor ladder DACs, the linearity errors would be of a certain sort. Resistors trimmed slightly off. Like bit 4 output is 16.3 (instead of perfect 2^4=16) to 32768 from bit 15 output(assumming bit 15 output is perfect). No matter what, the bit 4 output is always going to be in slight error, and consistently of that slight error.

For sigma-delta, noise shaping would be used. This of course would introduce a entirely different type of linearity errors, but given how sigma-delta works, the overall error would be less. It would seem much more difficult to get the ladder DACs to be just as linear given the difficultly of precision trimming of the resistors.

Now how does this correlate to what we hear? Those of you who have heard enough DACs, quality DACs that is of both kinds, know that resistor ladder and sigma-delta sound different and have different strengths. The best sigma-delta implementations sound highly detailed with sharp attacks. The best resistor ladder DACs sound smooth with natural timbre.

Would in interesting to see some linearity plots (output vs. bitcode), DNL, and INL plots of both kinds. Maybe there is something. Maybe not.

Maybe greater linearity = more resolving (it's true mathematically, but is it true subjectively?) Maybe linearity error plots with certain more predictable patterns = smoother more natural sound?

TBH, I dunno either.

What I can say though is that if a ladder DAC uses sample and hold, that automatically will introduce a little bit of roll off at the top and some amount of ultrasonic stuff.

Delta Sigma will not be nearly as rolled off at the top, but it will produce quite a bit of ultrasonic stuff.

There might be some interactions with the board, other components regarding the ultrasonics, but I dunno.

For sure the frequency response will be slightly different unless some sort of compensation is introduced for the ladder DAC.

Like you said, there will be different sources of non-linear issues due to precision. With 1-bit delta sigmas, if the signal does not follow a certain assumed uniform distribution model, things can get weird and spurs can appear at the output. There will also be some residual precision error form what I remember. Multi-bit, multi-stage, high-order delta sigmas with different levels of feedback (not just unity) can yield more interesting noise shaping characteristics, lower precision errors and maybe less prone to non-linear data dependent issues... also from what I remember.

Marvey · « **Reply #2 on:** October 01, 2014, 12:41:06 AM »

TI DAC8581. Industrial DAC chip which could be the one used in a well known NOS DAC.

It's a "16-bit" DAC. Well sort of. Look at the LSB error in the INL plot. I believe that INL error pattern is typical of ladder DACs.

Clemmaster · « **Reply #3 on:** October 01, 2014, 12:55:29 AM »

The DLE graph is pretty good, though.

Marvey · « **Reply #4 on:** October 01, 2014, 12:56:39 AM »

Quote from: Clemmaster on October 01, 2014, 12:55:29 AM

The DLE graph is pretty good, though.

Of course, it's a differential.

Anyways. This DAC is scary. Scary good. It's a 20-bit ladder (with tweaks I don't understand or are unclear) DAC with better than 1 LSB accuracy.
AD5791. $55 a pop at Mouser. And not because crazee audiophiles want it so Kingwa needs to buy 100s of them.

This DAC chip is definitely for missiles or MRIs.

schiit · « **Reply #5 on:** October 01, 2014, 01:02:52 AM »

Quote from: purr1n on October 01, 2014, 12:41:06 AM

TI DAC8581. Industrial DAC chip which could be the one used in a well known NOS DAC.

It's a "16-bit" DAC. Well sort of. Look at the LSB error in the INL plot. I believe that INL error pattern is typical of ladder DACs.

Um. Wow.

Clemmaster · « **Reply #6 on:** October 01, 2014, 01:04:02 AM »

It's a voltage output DAC, Kingwa won't like that

Marvey · « **Reply #7 on:** October 01, 2014, 01:08:34 AM »

Quote from: schiit on October 01, 2014, 01:02:52 AM

Um. Wow.

I think Chrysler used for those DACs for manufacturing. :-)

schiit · « **Reply #8 on:** October 01, 2014, 01:11:22 AM »

Quote from: purr1n on October 01, 2014, 12:56:39 AM

Quote from: Clemmaster on October 01, 2014, 12:55:29 AM
The DLE graph is pretty good, though.

Of course, it's a differential.

Anyways. This DAC is scary. Scary good. It's a 20-bit ladder (with tweaks I don't understand or are unclear) DAC with better than 1 LSB accuracy.
AD5791. $55 a pop at Mouser. And not because crazee audiophiles want it so Kingwa needs to buy 100s of them.

This DAC chip is definitely for missiles or MRIs.

Its also interesting to note that Analog Devices billed it as "THE INDUSTRY'S FIRST TRUE 20-BIT DAC" when it was introduced...in 2010.

It's unlikely that this would ever be used in audio, since it does not accept standard audio data formats (and, in fact, if you look at the datasheet for what you have to write into the DAC for every sample, it's even scarier.) Plus there's no EZ-Bake Oven "How 2 Uze 4 32/768 Arrdio" application note for it with Konvenient Plug-N-Go™ reference design. And, only 20 bits! Where's your buzzword compliance?

Another random note, taken from a quick scan: AD has a bunch of very linear DACs, including ones we'd kill for in the early days of audio, like quad 16-bit parts with less than 0.5 LSB nonlinearity across the band.

Final random note: The $55 AD5791s look to be the cheap "A" grade. "B" grade is actually better in AD-speak. $65 in 1000 pc quantities. That's about 10 top-shelf delta-sigma DACs there, or 40 AKM4396s, which are still very good.

Marvey · « **Reply #9 on:** October 01, 2014, 01:12:11 AM »

OK trying to find INL plots for audio DACs... Can't seem to find them. Now I wonder about those 20-bit, 24-bit and 32-bit claims. I can find graphs for a lot of high accuracy ladder DAC type chips on the Analog Devices site though. All the audio chips seem to omit this measurement.

For the heck of it, I'm going to write a computer simulation for an INL plot a typical ladder DAC. I can probably assume the resistor values / errors will follow a bell curve and we already know how a ladder DAC is laid out...

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

Marvey

DAC guts stuff, etc.

ultrabike

Re: Purely speculative - Rag, Yggy, Theta - how tech development affects sound, etc.

Marvey

Re: DAC guts stuff, etc.

Clemmaster

Re: DAC guts stuff, etc.

Marvey

Re: DAC guts stuff, etc.

schiit

Re: DAC guts stuff, etc.

Clemmaster

Re: DAC guts stuff, etc.

Marvey

Re: DAC guts stuff, etc.

schiit

Re: DAC guts stuff, etc.

Marvey

Re: DAC guts stuff, etc.

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