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Integral nonlinearity (INL), THD, etc., in multi-bit DACs
Integral nonlinearity (INL), THD, etc., in multi-bit DACs
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Old 8th April 2018, 04:26 PM   #1
hollowman is offline hollowman  United States
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Default Integral nonlinearity (INL), THD, etc., in multi-bit DACs

I think there are some original Philips engineers that hang out here at DIYA, so perhaps they should comment first

Anyway, back in Oct. 2015, on head-fi.org, Jason Stoddard (of Schiit Audio), made the following comments about one of the Schiit D/A products:

Quote:
Some fun facts about the AD5547CRUZ DAC used in Bifrost Multibit (for super techies only):

1. It features an integral nonlinearity (INL) plot that's better than +/-0.5LSB. This is a spec they never provide for audio DACs, because (a) it would be terrifying in the case of audio multibit DACs and (b) it is not possible to measure delta-sigma DACs in this way, since the output depends on the preceding and following samples.

2. The THD performance is actually scary good--far better than 16 bits. 16 bit level THD, from a theoretically perfect 16-bit DAC, is -96dB. Most 16 bit DACs from the Jurassic Age of Digital didn't hit this number. The AD5547 is -104dB, much better than 16 bit--and its noise level is down at the 22 bit level. And this is without the deglitching tricks applied to Gungnir Multibit and Yggdrasil.

3. It is a parallel input DAC. As in, the entire 16-bit word has to be written in at once, on 16 separate pins. This is very bizarre, since most DACs are serial in. Just one way that these are NOT easy to use for audio.
So, how much of the above is hype and how much is legit? (Again, our Dutch friends may respond first!)

Note that Schiit uses $$$ monolithic Analog Devices multi-bit DACs (not specifically designed for audio).

The AD5547 is $13 - $20 per chip!
The AD5791 (used in the Schiit top-of-the-line DAC) is $38 - $166 per chip!
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Old 9th April 2018, 03:38 PM   #2
hollowman is offline hollowman  United States
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About those modern AD multi-bit DACs (AD5547, AD5791) ...

It's a bit surprising that here on DIYA of all place (where multi-bits have survived and thrived while most of the high-end audio industry went sigma-delta), these DACs have been totally ignored.

In fact, I think only Braxy and some a-hole called "hollowman" has posted on these chips:
Schitt's flagship DAC uses a not-for-audio DAC chip. - diyAudio
Schiit Audio using AD5791 (modern R2R/multibit) - diyAudio

Come on guys .... Schiit's made a killing off their multi-bit dacs .. and no one in the DIY circle has experimented with the AD chip?
Don't tell me it's the up-front cost? Especially when compared to eBay listing of TDA1541a (double crowns), PCM63's, etc.
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Old 9th April 2018, 04:30 PM   #3
DPH is offline DPH  United States
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Simply put, proof is in the pudding, and there's a bunch of modern dac chips that supersede these from Analog Devices, especially for audio applications.

Given the multibit obsession on diyaudio has not been one pushed by the folks with the technical wherewithal, its no surprise that no one has worked with these chips.
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Old 9th April 2018, 04:34 PM   #4
scott wurcer is offline scott wurcer  United States
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They require a lot of extra engineering like de-glitching to use them for audio. This was tried way back in 1986 or so and failed. The TDA/BurrBrown/AD1862/5 style multi-bit converters won out until S-D appeared.

abraxalito's post is a good read, I personally don't like the tone of some of the Schiit posts and as he points out they do contain some errors.
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Old 9th April 2018, 05:01 PM   #5
DPH is offline DPH  United States
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I should be more careful in what I meant, as these multibit dacs are good for what they're designed for, but it's a case of square peg round hole. That versus using modern sigma delta designed for audio.
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Old 9th April 2018, 10:31 PM   #6
scott wurcer is offline scott wurcer  United States
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I forgot to mention I have some data on those DAC's using the dreaded sample and hold de-glitcher, but I can't share the results. Quite impressive though there is extra circuitry needing careful layout, nothing's for free.

@hollowman - I did better than being banned, I got a personal dressing down that my daughter found and asked "Why do these people hate you"?
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Old 9th April 2018, 11:47 PM   #7
hollowman is offline hollowman  United States
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Another type of DAC that has not appeared in the DIY community is the FPGA-based DAC. These things are found in Chord DACs, etc.
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Old 9th April 2018, 11:53 PM   #8
DPH is offline DPH  United States
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There's a couple of them around DIYAudio as well! Soekris's for one.
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Old 10th April 2018, 12:41 AM   #9
hollowman is offline hollowman  United States
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Quote:
Originally Posted by DPH View Post
There's a couple of them around DIYAudio as well! Soekris's for one.
TTBOMK, Soekris is a discrete DAC: That is, the D/A part of the Soekris device, not the whole thing (which may use FPGA for filters, etc.).
The Chord uses FPGA for the actual D/A conversion.
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Old 10th April 2018, 02:20 AM   #10
abraxalito is online now abraxalito  United Kingdom
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Amir made some measurements (on ASR : Measurement and Review of Schiit BiFrost Multibit DAC | Audio Science Review (ASR) Forum) of one of Schitt's DACs that uses the AD5547. The result of interest to me was the linearity, which looks quite appalling. Mike Moffat said that the result shows a broken DAC but another guy on a different forum found pretty much the same issue with his measurements.
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