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Old 16th February 2015, 11:03 PM   #71
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Any one as any idea what kind of filter is dCS using in their famous R-2R DAC?

See this link http://audiofast.pl/main.asp?idm=1&i...u=635&wersja=1

There is twonice White Papers
-''A Suggested Explanation For (Some Of The) Audible Differences Between High Sample Rate and Conventional Sample Rate Audio Material''
-''Effects in High Sample Rate Audio Material''

where they discuss filter types and their perceive sound. May be useful as well...

Last edited by Algar_emi; 16th February 2015 at 11:12 PM.
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Old 16th February 2015, 11:35 PM   #72
leehan is offline leehan  United Kingdom
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Originally Posted by Algar_emi View Post
Any one as any idea what kind of filter is dCS using in their famous R-2R DAC?
Page 19: http://www.dcsltd.co.uk/wp-content/u...nual-v1_0x.pdf

They recommend filter types per sample rate in a quite unexpected way (for me). If correct, it may invalidate our assumption of developing a decent 44.1kHz filter and porting it to higher sample rates.

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Originally Posted by Algar_emi View Post
See this link dCS - best audiophile hi-end digital to analog converters

There is twonice White Papers
-''A Suggested Explanation For (Some Of The) Audible Differences Between High Sample Rate and Conventional Sample Rate Audio Material''
-''Effects in High Sample Rate Audio Material''

where they discuss filter types and their perceive sound. May be useful as well...
"Effects" paper (http://audiofast.pl/pdfs/effects.pdf) may be related to this...
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Old 16th February 2015, 11:55 PM   #73
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Originally Posted by leehan View Post
Page 19: http://www.dcsltd.co.uk/wp-content/u...nual-v1_0x.pdf

They recommend filter types per sample rate in a quite unexpected way (for me). If correct, it may invalidate our assumption of developing a decent 44.1kHz filter and porting it to higher sample rates.



"Effects" paper (http://audiofast.pl/pdfs/effects.pdf) may be related to this...
I stepped back from doing greater than 44.1kHz versions of the filters because the requirements are significantly different. With 44.1kHz and 48kHz the narrow band between 20kHz and fs/2 or Nyquist (22050Hz and 24000Hz respectively) make filter design a matter of balancing trade-offs and compromises. Once you move to 96kHz, Nyquist is at 48000Hz so you have up to 28kHz of bandwidth in which to attenuate. This makes filter pre and post ringing much less of an issue.

I'd be a bit cautious about reading too much into the effects paper. The article looks at the complete chain of ADC and DAC using analogue tape as a source, and the authors were manipulating filters on both the ADC and DAC in the tests.

I'd also note the dcs paper is from 1997. Much of the move towards slow roll-off filters for 44.1kHz has occurred since the mid-2000's, so keep in mind that Mike Story's work predates these later developments.

Last edited by spzzzzkt; 17th February 2015 at 12:17 AM.
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Old 17th February 2015, 01:28 AM   #74
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Good comments. Latest Debussy Dac has only two filters. Thanks SB

Last edited by Algar_emi; 17th February 2015 at 01:45 AM.
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Old 17th February 2015, 03:29 AM   #75
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I haven't had a serious listen but I'll give the NOS another run in the day or so.
The filters seem to be piling up, so it's hard to know where to go next.
OK, I have the NOS "filtering bypass" installed. Too be honest it's not anywhere as bad as the spectrum would suggest.

The sound is thicker, and possibly little more ponderous than the other filters. There is no sense of the shoutiness on the Lydon vocals on Album. There are perhaps hints of a slightly metallic haze on the voice in the sections that were previously shouty.

On Miles' "So What", it actually sounds impressively natural. There is a nice level of detail - you can really get a sense of the drummer using brushes for example.

Despite what I've said previously I wouldn't dismiss this NOS bypass without a decent listen. If nothing else it's a salutary lesson in what the DAM1021 can do without any filtering

cheers
Paul
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Old 17th February 2015, 08:56 AM   #76
jaffar is offline jaffar  Russian Federation
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Originally Posted by spzzzzkt View Post
"Nasty" is such an emotive term.

It's worth having a read of Doug Rife's paper on Oversampling Theory (link in the first post). There is an interesting section "Upsampling ameriolates differential non-linearity".

Quote:
Upsampling provides another method for averaging away differential non-linearity but without requiring multiple DACs. The ultrasonic image energy that a slow roll-off anti-imaging filter presents to the DAC can be thought of as a form of dither. As mentioned above, the image spectrum is folded which has the effect of de-correlating it from the baseband audio signal thus making it random for all practical purposes.
These statements are highly objectionable.

Mirror image = uncorrelated spectrum? Far from the truth...
Dither is random and has completely uncorrelated spectrum. The folded image is not.
Doug Rife makes wrong assumptions that foded images have de-correlating effects (like dithering which decorrelates quantization errors).

Upsampling has many benefits. The folded images of slow roll-off filters are none of them... The "nasty" artifacts indeed.
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Old 17th February 2015, 10:27 AM   #77
TNT is offline TNT  Sweden
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Good points jaffar!

//
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Old 17th February 2015, 12:41 PM   #78
Eldam is offline Eldam  France
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Originally Posted by spzzzzkt View Post
OK, I have the NOS "filtering bypass" installed. Too be honest it's not anywhere as bad as the spectrum would suggest.

The sound is thicker, and possibly little more ponderous than the other filters. There is no sense of the shoutiness on the Lydon vocals on Album. There are perhaps hints of a slightly metallic haze on the voice in the sections that were previously shouty.

On Miles' "So What", it actually sounds impressively natural. There is a nice level of detail - you can really get a sense of the drummer using brushes for example.
Good ! I believe because the room and time delays with walls interactions : NOS is not the same when listen to with headphones vs Floorstanders. The room have to help a little in the highs with NOS acting like a pad of interface.

Certainly a mixed way to find between NOS and FIR filter like TotalDac made ? This is not to said than upsampling can be bad but it seems to involve a huge work to find something which sounds pleasant !

Paul, did you find a better dynamic with NOS ? Especially in the low end and medium ? Cant it rock now ? (bass string, percussions, drums ?)
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Old 17th February 2015, 01:50 PM   #79
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Hi
Is it possible to post the .txt file for the NOS filter? Is it the same filter as posted earlier in this thread?

Best regards
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Old 17th February 2015, 02:21 PM   #80
TNT is offline TNT  Sweden
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Good ! I believe because the room and time delays with walls interactions
The "brickwall" filter I posted has excellent phase coherence. The signal spend more time in the filter but low and high frequencies come out with the same time relation that they got in to it. You have to wait a few extra milliseconds before you can hear the song after you hit play - thats the drawback in the time department

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