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Old 26th August 2004, 06:16 AM   #11
hacknet is offline hacknet  Singapore
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oh okay... i thought i had a lump of crap sitting around(thou it sounds reasonable).

thank You all for your reassureances!
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Old 26th August 2004, 07:29 AM   #12
Werner is offline Werner  Europe
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Quote:
Originally posted by thoriated

This Gibbs Phenomenon ringing is an artifact of the excessively narrow transition band from non-minimum phase brick wall filtering which is widely acknowledged to add coloration to the high frequencies.
Nope.

For proper reconstruction Shannon prescribes that a Sin(x)/x filter be used. This is the well-known Sinc(x) function whose impulse response ripples from the Big Bang right to Judgment Day. The ripples are a necessary condition for the reconstruction of a sampled band-limited source signal to be correct and complete. In other words: at playback these ripples are not a distortion or a deviation, insofar the oversampling filter in the CD-player approximates the theoretical Sinc function.

Now, using such filters as part of the decimation stage of an oversampling *ADC* is a different kettle of phish.

To the original poster: testing CD-players with synthesized square wave signals is a bit pointless as such signals are not band-limited, illegal in Shannon's world, and impossible to get onto a CD with a legal recording process.

They are handy for revealing the internal reconstruction filter's properties, though.
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Old 26th August 2004, 08:24 AM   #13
hacknet is offline hacknet  Singapore
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may i ask what is a recommended test to determine "technical" quality of a CDP?
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Old 26th August 2004, 11:17 AM   #14
MikeB is offline MikeB  Germany
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Hi all !

You are talking about ringing...
The "distorted" squarewaves you are showing are not distorted at all,
that's what a squarewave looks like after having ripped off all high freqs. (if done properly)

What is the point in reproducing a perfect squarewave, containing
frequencies up to several MHz ? It will only kill your poweramp.

A smoothed squarewave without this ringing is distorted, it contains
severe odd harmonics. (mainly 3rd and 5th harmonics)

If you learn about fouriercomponents you understand what i am talking about.

This means, a squarewave reproduced like on your images is a
perfect reproduction of squarewaves, just without deadly high freqs.

I can't believe that you are complaining about something that is really properly done...

Mike
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Old 26th August 2004, 12:37 PM   #15
Charles is offline Charles  Germany
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Default some ringing pics

Hi there,,

I have some pics of different digital/analog filters and how they relate to each other on my site:

http://www.mother-of-tone.com/timeband.htm

Charles
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Old 26th August 2004, 12:49 PM   #16
hacknet is offline hacknet  Singapore
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wow, this is interesting..
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Old 26th August 2004, 09:06 PM   #17
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quote:
Originally posted by thoriated

This Gibbs Phenomenon ringing is an artifact of the excessively narrow transition band from non-minimum phase brick wall filtering which is widely acknowledged to add coloration to the high frequencies.


Nope.

'Nope' what? Is there anything factual I posted that you dispute, or do you simply happen to disagree with my assertion that brick wall filters are not ideal sonically? Gibb's Phenomenon is typically referred to as 'ringing'. Also, it is not permitted to assume that my use of the word 'artifact' equates with your use of the terms 'distortion' or 'deviation', because it doesn't. IAC, such a characteristic would not be desirable in filter where an optimal settling time with a monotonic impulse function is desired, so going on about the 'perfection' of the Sinc function as implemented in an audio application filter with an absolutely flat passband response & vanishing transition band rather misses the point, AFAIC.
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Old 26th August 2004, 10:59 PM   #18
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I'd take little notice of Werner if I were you, he is simply a contrary fellow. If Shannon was able to post here, he would contradict him.
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Old 27th August 2004, 08:38 PM   #19
Gyula is offline Gyula  Hungary
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Send a message via Yahoo to Gyula
You have a very good site.

Gyula
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Old 27th August 2004, 08:51 PM   #20
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Quote:
Originally posted by hacknet
may i ask what is a recommended test to determine "technical" quality of a CDP?
Using a sine wave generator, record in your computer a wave file which goes from 20 to 20Khz. Keep it about 80 % of full scale.

Make a CD of that.

When you play back that CD, you will initially hear just the sine wave.

As the frequency goes up, on a poor player, you will begin to hear subharmonics..My computer sound blaster card starts to do this at about 4 Khz..it sounds like heterodyne whistling (ask some other old fart what that is...I'm gonna be in vacation mode in about 10 minutes..)

The depth of the reconstruction filter will determine the extent and amplitude of these subharmonics..since the reconstruction filter is not infinite in length, the subharmonics will be there. However, it is not very difficult to exceed the output quality of my sound blaster...

Cheers, John
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