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03/23/18 at 12:16:04 


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Why Hi-Resolution is needed for digital sources (Read 182 times)
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Why Hi-Resolution is needed for digital sources
03/04/18 at 16:42:10
[/color]Just found a great video explaining (for digital sources) why high-resolution audio is critical.

To give you a little back ground before you watch the video:

1) The Nyquist–Shannon sampling theorem establishes a sufficient condition for a sample rate that permits a discrete sequence of samples to capture all the information from a continuous-time signal of [color=#009900]finite bandwidth
, and that the sufficient sample-rate is twice the bandwidth (ex. a 24kHz bandwidth could be represented by a 48kHz sample-rate)

2) The key point here is "finite bandwidth", and that finite bandwidth is not possible with current filtering technology.  So the real world implementation of this theorem will introduce error into the signal if that signal is not perfectly bandwidth limited.

3) To help minimize the error introduced the sampling rate is increased (192 KHz, 384kHz, etc.) so that filters with a lower roll-off can be used.

In my opinion out of all the errors introduced by not being able to perfectly bandwidth limit the signal, the worst are: 1) phase error and 2) ringing artifacts (like pre-echo).  I think our ears are extremely sensitive to phase errors and pre-echo.  Especially pre-echo, because in the real world you can't hear a sound before it happens Smiley

The youtube video is titled "The truth about Nyquist and why 192 kHz does make sense"
Here is the link:

Also, this comment by Zachary Doering about the video brings up some excellent points:

[/color]"I think part of the discussion that needs to really be explained is the effect of band limiting in both the digital and analogue domain, any band limiting anywhere will causing ringing artifacts, any cable and equipment you use will do this as well. This is why I find double blind tests of audio not truly scientific to disprove high-resolution. If you band limit a cable to 10k due to capacitance that will have an audible effect and therefore you really are not isolating all variables scientifically. The provenance of the signal is no longer intact.

When I hear Pro-Audio people, or people like Monty, tell me they cannot hear the difference, I would want to ask them how many looms of cabe and what kind of monitors are you using? what are their crossover freqs? Any of those things can introduce tons of ringing artifacts that will make high res compromised, or really any signal.

To add to your point Hans, I remember dCS had a white paper on their website some time back, that explained what extreme band limiting in the digital domain did, and they showed it caused phase and amplitude shift, they had snapshots of it on oscilloscopes. This is known in physics as the Gibbs Phenomenon. It is never explained by the apologists of just sampling at nyquist. Any filtering you do will cause a ripple effect in the audio much like throwing a rock in a pond. Humans can hear the harmonics of fundamental frequencies way above 20k and the phase and ringing artifacts smear in the time domain. All of these things are important. If high order harmonics were not important then, for example, the type of piano or guitar you use and how it resonates would be inconsequential because they are all generating the same fundamental frequencies, but as any musician will tell you, it does matter. Why? due to the distribution of how those frequencies sit, and all of this information happens in the upper end of the frequency range.

Personally I have heard the effects of high sample rate and DSD, but it does require a controlled set up, actually I found that tube gear demonstrates it the most due to it's high slew rate, and when I managed a high end store, we had some tube preamps that could go to 100k and high sample rate was very audible on those especially DSD. I also had a CD player that had a band limit of 80k and could select the CD layer at 16/44.1k and the SACD layer, I was even able to demonstrate to audiophiles who didn't believe in DSD that it made a difference it was very audible on a non band limited player.

In short I think the people who maintain there is no difference either have never heard live music or lack the equipment and discernment to hear the difference, because the changes are very audible even to the un-initiated on the right system.  

Simply put Nyquist is sufficient to prevent aliasing, but not sufficient to portray real life, and we are after it sounding like real life, not to just no longer have aliasing artifacts.

To use another analogy 24fps will allow the human eye to perceive motion in still pictures, but it doesn't look as if we are actually seeing through a window in real life. The only thing that can approach that is a high resolution screen at a high frame rate, and that is what we want with audio."

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« Last Edit: 03/08/18 at 20:44:13 by Steve Deckert »  
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