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Topic: CD artifacts (Read 4782 times) previous topic - next topic
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CD artifacts


I was watching a youtube video about the PS Audio Directstream DAC and how it improves the sound quality of CD
by converting to DSD.  I think the idea is that when a CD is created its sampled at 44.1khz (highest frequency
captured is 22khz) and this causes problems because presumably any higher frequencies leave unresolved 'traces' at 44khz
(distortion). By interpolating the signal we can upsample to 176khz (DSD) and resolve out what would otherwise be noise at these higher frequencies. Does anyone know if this is about right or completely wrong?

Re: CD artifacts

Reply #1 –
Wrong, all modern DACs on playback internally up-sampling to remove the aliasing issue. Most are delta sigma which are 1 bit dacs, so nothing the world has not been doing for the last 30 years...

Re: CD artifacts

Reply #3 –
If you're looking for such content, this Youtube channel is much better.
Loudspeaker manufacturer

Re: CD artifacts

Reply #4 –
I was under the impression that the Directstream DAC was 'high end' (some $5000) and converting the PCM to DSD was unique.
So you saying that most DAC's ($500) will be converting PCM to a form of DSD (1 bit delta sigma) and then to analogue.
 
Re: It is nonsense:
I thought it was common knowledge that PCM 44.1khz cut off causes problems - the analogy is echoing off a wall. Presumably
there would'nt be any point upsampling unless it allows you to undo the echoing.

Re: CD artifacts

Reply #5 –
Just checked the youtube channel - its not available to the UK.

Re: CD artifacts

Reply #6 –
Quote from: Paul77 on
I thought it was common knowledge that PCM 44.1khz cut off causes problems - the analogy is echoing off a wall.

I think you are referring to aliasing, the audio signal is mirrored at half fs (not 44 but 22).
That is indeed the case and to filter it out you need a very steep filter (brickwall) because you want to preserve the audible range at one hand but all signal must be gone before you hit ½ fs.
I believe it was the second gen of CD player (late 80’s)  that applied 4 times oversampling and later 8 times oversampling. Of course we still keep the alias (in digital everything remains the same) but
8x22 = 176 kHz for the first alias to appear. No need to brickwall anymore.
Please observe that this has nothing to do with DSD
Maybe this link to my website is of use: http://www.thewelltemperedcomputer.com/KB/Sampling.htm


TheWellTemperedComputer.com

Re: CD artifacts

Reply #7 –
Quote from: Paul77 on
PS Audio Directstream DAC

This US $6,899 DAC can be found here: https://www.audiosciencereview.com/forum/index.php?threads/review-and-measurements-of-ps-audio-perfectwave-directstream-dac.9100/

You might compare to e.g. https://www.audiosciencereview.com/forum/index.php?threads/review-and-measurements-of-rme-adi-2-dac.2582/

Gives you a taste of the performance of a  PS audio product and a $999 RME
TheWellTemperedComputer.com

Re: CD artifacts

Reply #9 –
Aliasing happens during sampling/digitizing (recording) or when downsampling, not during digital-to-analog conversion (playback).

I once had a soundcard with no filtering.   For some reason (I don't remember why) I hooked-up an oscilloscope and I was surprised to see a "clean" stair-stepped" waveform!    I hadn't noticed anything "wrong", but the harmonics are at the sampling frequency or higher so of course I couldn't hear them.   (Plus, they were probably filtered-out mechanically by the speakers and maybe the amplifier was band-limited too.)

With modern DAC chips it's cheap and easy to build a DAC that's better than human hearing.  If you're not getting excessive noise from your soundcard, your regular soundcard/soundchip is probably better than human hearing.
 

Re: CD artifacts

Reply #10 –
Quote from: DVDdoug on
Aliasing happens during sampling/digitizing (recording) or when downsampling, not during digital-to-analog conversion (playback).

It also happens during digital-to-analog conversion, but it's typically called imaging rather than aliasing. You still need a low-pass filter after the DAC to remove all signal above the Nyquist limit (half the sampling frequency).

Re: CD artifacts

Reply #11 –
Re: Monty Montgomery video:
Had a scan through didn't seem to find anything on AtoD aliasing or as above DtoA imaging.
I think the original PS Audio video was referring to DtoA 'imaging' since it also mentioned the low pass filter.

Re: CD artifacts

Reply #13 –
Quote from: Paul77 on
I was under the impression that the Directstream DAC was 'high end' (some $5000) and converting the PCM to DSD was unique.
So you saying that most DAC's ($500) will be converting PCM to a form of DSD (1 bit delta sigma) and then to analogue.

20 or so years ago, yes that was very common.  Most are actually multibit the last 15 years, since fabrication improved and it got a lot easier to make better converters.  I think most (all?) dedicated DSD devices no longer use 1 bit in practice anymore either.  If you search on this forum, there were many topics about this in the early 2000s. 
 
Quote from: Paul77 on
Re: It is nonsense:
I thought it was common knowledge that PCM 44.1khz cut off causes problems - the analogy is echoing off a wall. Presumably
there would'nt be any point upsampling unless it allows you to undo the echoing.

What are you asking?

Re: CD artifacts

Reply #14 –
Quote from: Paul77 on
I thought it was common knowledge that PCM 44.1khz cut off causes problems - the analogy is echoing off a wall.
Indeed it is common fodder for trolling technical forums. Now remember to feign all insulted as a "newb" with 8 posts, didn't read TOS rules, etc, etc.
We've seen it all before, many times, no worries. Have fun.
Loudspeaker manufacturer

Re: CD artifacts

Reply #15 –

After reading Roseval's "An introduction to computer audio" - this makes what was in the
PS Audio upsampling and directstream DAC videos a bit clearer.
 
From Roseval's article:

Inherent in the mathematics involved in DtoA conversion higher frequency multiples are created.
At 44.1khz these aliases start at 22.05khz

You can remove these with a low pass filter. A filter at 20khz will remove everything before the alias start.
But this introduces phase distortion and pre-ringing artifacts.

By oversampling, say 8 times, the mathematics in the DtoA conversion creates the aliases at
330khz. I was expecting this to be half the new sampling rate - but anyway the idea is that you have changed
the maths.



The "echoing off a wall" analogy I referred to must be referring to the "pre-ringing artifacts" you
get from a low pass filter cutting everything off at 20khz. I can see the analogy but it could do with more
detail.


Re: CD artifacts

Reply #16 –
The Fear Of Ringing is the bigfoot for audio peddlers for maybe 20 years now. It also can be shown in funny pictures. Terrific!
Is troll-adiposity coming from feederism?
With 24bit music you can listen to silence much louder!

Re: CD artifacts

Reply #18 –
Quote from: Paul77 on
The "echoing off a wall" analogy I referred to must be referring to the "pre-ringing artifacts" you
get
There will be such "referral" ambiguity when making stuff up along the trip.
Loudspeaker manufacturer

Re: CD artifacts

Reply #19 –

Thanks for the link Roseval I've had a look but its quite technical so will take
a bit more reading.

Re: CD artifacts

Reply #20 –

On the "echoing off a wall" reference - the source of this was the following
comment on the video "How does upsampling increase information?"

"A good way to explain the filter problem is to consider a square ledge in a tank of water - a wave will reflect off the sharp edge.
In music you get the artifacts as ring harmonics.  So if you have a soft filter the wave does not reflect and you don't get the wave
"bouncing" of the band pass filter."

Re: CD artifacts

Reply #21 –
Why is that a problem?
a fan of AutoEq + Meier Crossfeed

Re: CD artifacts

Reply #22 –
Quote from: Paul77 on

On the "echoing off a wall" reference - the source of this was the following
comment on the video "How does upsampling increase information?"

"A good way to explain the filter problem is to consider a square ledge in a tank of water - a wave will reflect off the sharp edge.
In music you get the artifacts as ring harmonics.  So if you have a soft filter the wave does not reflect and you don't get the wave
"bouncing" of the band pass filter."

That is a bad explanation because it does not make sense and doesn't explain anything. It is just someone telling you their opinion that a "soft filter" is better for some reason. 

Re: CD artifacts

Reply #23 –
It's common knowledge.
Overheard some fellas talking about it at the bait shop
Loudspeaker manufacturer

Re: CD artifacts

Reply #24 –
Quote from: Paul77 on
Does anyone know if this is about right or completely wrong?
With the right signal it is equally as easy to demonstrate ringing at 176-bit DSD. This is the wrong line of thinking.

Is the result audible?

https://en.m.wikipedia.org/wiki/Law_of_excluded_middle