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 Post subject: DSD and the BB DSD1793
PostPosted: Wed Apr 23, 2014 6:23 pm 
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Cow

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T,

on the DSD1793.

DSD is filtered first, with the choice of analog filter settings, then is sent to the DS modulator for conversion, followed by one final analog filter.

What happens to the DSD signal once in the modulator? It is already DS modulated, so it doesn't need to be re-modulated. I am assuming and guessing that what happens is it at least undergoing a conversion to multi-bit delta sigma. I am guessing once again, that rather than being passed through, it is re-modulated, but mathematically the signal should be the same, like a 1:1 conversion? And this is why the analog filtering is applied before the signal goes to the DS modulator, to minimize the effect of the existing noiseshaping during this process. Of course there is a final analog filter at 75khz applied to all signals at the end of the signal chain. But only DSD gets this double analog filtering.

Again, these are total guesses. If you could comment on what actually happens, that would be appreciated.


Thanks

Andrew


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PostPosted: Thu Apr 24, 2014 2:23 am 
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Muriel
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Hi,

ball3901 wrote:
on the DSD1793. DSD is filtered first, with the choice of analog filter settings, then is sent to the DS modulator for conversion, followed by one final analog filter.


No. Look up the DSD1700 Datasheet, or Miska's DSD DAC. It works in precisely the same way, Burr Brown invented that approach in the late 90's...

BTW, for DSD decoded directly there is no modulator. Just bit-switches. And low-passes.

Ciao T

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PostPosted: Thu Apr 24, 2014 2:28 am 
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Cow

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Ok thanks

I think where I get lost is in the cascading filters. I suppose it is just a necessity of a design to handle both PCM and DSD..


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PostPosted: Thu Apr 24, 2014 3:10 pm 
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Cow

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While I am here, let me run a thought by everyone.

Why DSD sounds like it does. I am inclined to believe this guy...

http://www.positive-feedback.com/Issue66/pcm_dsd.htm


Furthermore, all one has to do is look at graphs to see that DSD128 has a noise curve that is not all that increased over any typical DAC that uses Delta Sigma conversion.

So as far the effect described in the above post, DSD128 shouldn't really sound all that different from what we typically expect to hear from these modern time splicing DACS.

If one REALLY wants to get that trademark DSD sound, you need a significant increase in the noise. Voila, your answer is DSD64.

It seems to me that as you increase the oversampling, you lose more of the noise, therefore you lose more of that 'trademarked' sound.


Just some more random thoughts from an enthusiast who really cares too much...


Andrew


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PostPosted: Thu Apr 24, 2014 3:51 pm 
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Muriel
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Hi,

ball3901 wrote:
Furthermore, all one has to do is look at graphs to see that DSD128 has a noise curve that is not all that increased over any typical DAC that uses Delta Sigma conversion.


You want graphs? Here you can get graphs:

http://www.diyhifi.org/forums/viewtopic.php?f=15&t=2331&start=75#p49264

Ciao T

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PostPosted: Thu Apr 24, 2014 4:10 pm 
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Muriel
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Hi,

ball3901 wrote:
Why DSD sounds like it does. I am inclined to believe this guy...

http://www.positive-feedback.com/Issue66/pcm_dsd.htm


Lynn generally knows his onions. but I think he is off base for BUD.

Here is why.

Any analogue recording transferred from tape always had enough dither to linearise 16 Bit converters. Both A2D and D2A.

Any recording made with microphones has enough dither from the microphones noise to dither any decent 18 Bit PCM converter.

More ultrasonic dither does not really help.

We can use very fast IC's or discrete circuitry for bits after the DAC, or have passive filters before we hit slower stuff. That takes care of glitch energy etc.

All we need are a few good > 18 Bit real resolution multibit converters that run at least at 1Megasample/Second.

Then we can get decent PCM, no issue.

12 Bit Flash or Pipeline ADC's exist that are that fast, making a 6 Bit discrete Flash/Pipeline ADC for the upper bits is easy.

Why trying to keep flogging the dead single bit horse in a day and age where we can have 50 Megasamples/Second at 10 Bit?

This is like the bleedin Amish and their Horse-carts, of course you can do it, but why?

Ciao T

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PostPosted: Tue Apr 29, 2014 2:25 pm 
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Cow

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Kuei Yang Wang wrote:
Hi,

ball3901 wrote:
Why DSD sounds like it does. I am inclined to believe this guy...

http://www.positive-feedback.com/Issue66/pcm_dsd.htm


Lynn generally knows his onions. but I think he is off base for BUD.




Well, most of that is way above my pay grade. As far as that article is concerned, it is this statement that stands out to me...

"Well, I'm pretty sure (that's not 100% sure, but it's close), that most of the analog-like smoothness of DSD is the effect of the ultrasonic noise spectra on the first and second analog stage."


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PostPosted: Tue Apr 29, 2014 3:56 pm 
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Muriel
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Hi,

ball3901 wrote:
Well, most of that is way above my pay grade. As far as that article is concerned, it is this statement that stands out to me...

"Well, I'm pretty sure (that's not 100% sure, but it's close), that most of the analog-like smoothness of DSD is the effect of the ultrasonic noise spectra on the first and second analog stage."


Agreed.

It is interesting to look at the spectrum of a "non-oversampling" DAC playing music or pink noise (one might call pink noise an "idealised acoustic music spectrum") and to compare that to DSD...

Now I remember that in the beginning non-oversampling DAC's were claimed to cause amplifiers/tweeters/supertweeters (delete or add as appropriate) to blow up, on top of causing cancer or some such. The same kind of people now tend to promote DSD andClass D amplifiers...

Ciao T

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PostPosted: Tue Apr 29, 2014 6:37 pm 
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Goat

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Kuei Yang Wang wrote:
one might call pink noise an "idealised acoustic music spectrum"
I often leave my small system playing pink noise on gapless repeat. Good for concentration and also keeps the system warmed up and unclogged :finga:
Yeah, I find music can sound better after some pink noise (psychoacoustics?).
HereĀ“s some good sounding uncorrelated pink noise at -20dBFS 44.1KHz.
http://www.sendspace.com/file/r617cn


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