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Old 26th August 2012, 02:12 AM   #27001
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Originally Posted by abraxalito View Post
So you have an ideal brickwall AAF with no overshoot in the time domain whatsoever?
There is none in the A/D/A conversion, but bandlimiting can cause variable group delay issues, depending on implementation and your definition of "issues". The take-away word here should hopefully be implementation. I understand that some fancy new home D/A convertors give the user a variety of filters to choose from on the playback end. Might be fun for advanced homebrewers.

It's always worth keeping in mind that all mechanical widgets will add group delay "issues" to the sound, including speakers and rooms. There's no such critter as verbatim reproduction.

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Old 26th August 2012, 02:31 AM   #27002
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There is none. The bandlimiting itself can cause variable group delay issues, depending on implementation, but it's not inherent in the A/D/A conversion process.

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None? No Gibbs type phenomena due to the sharp bandlimiting? No infinite negative or infinite positve ringing energy from the ideal sinc function based bandlimiting reconstruction filter? Really? You might want to have another look at those theories by Shannon and Nyquist. I think you'll find that the presence of such time-domain distortions are actually essential to perfect frequency-domain reconstruction. These are not group-delay or phase distortions. The time-domain distortions I'm refering to provide the missing frequency-domain signal content not directly captured by the original sampled points.

The sampling theorem itself features both positive and negative infinities as a signal requirement. That means perfect sampling and reconstruction assume a perfectly constant signal, constant to the degree that such signals should have existed since the big bang and will continue to exist until the end of the universe. Obviously, that is not possible, but what it does tell us is that while bandlimited sampling and reconstruction is theoretically perfect for signals which carry only frequency-domain sensitive information, it is not perfect for signal which also carry time-domain sensitive information. This, IMHO, has been THE flaw with audio CD from the start. The time-domain sensitive nature of music recieved little to no consideration when the format was defined.

So, CD gave us perfect sound forever, as far as spectrum analyzers are concerned, but not as far as the time-domain sensitive instrument such as the human hearing system is concerned.
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Last edited by Ken Newton; 26th August 2012 at 02:35 AM.
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Old 26th August 2012, 02:40 AM   #27003
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Do you listen to impulses and step functions? There is a direct relationship between the time and frequency domain responses of a system.
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Old 26th August 2012, 02:45 AM   #27004
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sure - just list all of the properly blinded, psychoacoustically controlled listening tests that shows they're audible with music - even for 10% of the listening population

after all shouldn't "night and day" differences be able to AB/Xed?
Would that be the same population that is perfectly happy listening to MP3 that you're refering to? As far as the 10% who you assume to be more observant listeners, perhaps you would care to list those "properly blinded" listening test which show an inability for any listeners to distinguish sharply bandlimited CD digital recording and playback from say, 100% analog low-noise mastertape recording and playback.
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Old 26th August 2012, 02:59 AM   #27005
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The phonograph had 100 years of development before the CD was introduced. At that time most of the records sold were produced by well trained and experienced crews. Now the same level of skill is present in some CDs. But at the initial release there were lots of issues that were thought to be unimportant but turned out not to be. There was also a learning curve on how to best record for digital.

Now the difference between what can be delivered by the current CD standard and what is being encoded is converging. In live sound more resolution in the DSP is used. However most of the pros I know prefer the sound of cost no limit analog, but use digital mixing consoles for all of the other advantages.

Now my current system project uses a digital board as there are only two analog sources, the announcer and anthem singer. As the anthem singer uses a wireless microphone, the digital "losses" are not an issue. The big problem is the digital link from the console to the audio power amplifiers.

One can use Cobranet for the link, but it has design limits that I prefer to avoid. AES is up to the quality required but has transmission length issues. So I will have to build my own fiber transmission system. So to say digital is as fully developed as were records is probably not accurate.
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Old 26th August 2012, 03:05 AM   #27006
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Do you listen to impulses and step functions? There is a direct relationship between the time and frequency domain responses of a system.
If there is any frequency content near the upper bandlimit then yes, we are in part listening to the system impulse response. Otherwise, bandlimited sampling theory has no import.

Yes there is a direct mathematical relationship between the two domains. It is the Fourier transform. What one needs to understand is that the more rectangular (perfectly bandlimited) the signal channel is in the frequency-domain, the less perfect will be it's transform in the time-domain. This is the fundamental trade-off of bandlimited sampling and reconstruction.

To have both perfect frequency and time domain repsonses requires oversampling well beyond what's required to perfectly capture the frequency-domain content alone. For example, look at the sampling rates of digital oscillloscopes. You'll find that they sample at many times what's required to meet Nyquist for their maximum specified input signal bandwidth. This is because an oscilloscope is primarily a time-domain tool. Brickwall bandlimiting filters, such as utilized with CD, would produce unacceptable distortion of the oscilloscope's time-domain waveform.
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Old 26th August 2012, 03:08 AM   #27007
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Originally Posted by Ken Newton View Post
This, IMHO, has been THE flaw with audio CD from the start. The time-domain sensitive nature of music recieved little to no consideration when the format was defined.

So, CD gave us perfect sound forever, as far as spectrum analyzers are concerned, but not as far as the time-domain sensitive instrument such as the human hearing system is concerned.
There is no flaw with CD, no more than any other type of sound reproduction mechanism. Yes, there all sorts of subtle distortions one can point the finger at, inherent in the process of acquiring and reconstituting the waveform structure, but the ear/brain is amazingly accommodating provided you both supply it sufficient information, and also not overload it with highly unrelated material. Faults which a lot of digital is prone to, unfortunately.

An analogy for getting digital sound reproduction right is trying to use an extremely powerful set of binoculars. If with the latter the focus is not perfect then the image will be a blurry mess, the depth of field is so restricted that maladjustment by just a small amount makes the viewing hopeless. Plus, the binculars have to held totally stationary with respect to the viewed object, otherwise you'll get a headache from trying to keep track of what's there. But, get it right, and then the amount of detail from so far away you see is amazing, and you appreciate what a marvellous instrument that viewing aid is. That's how digital is, or at least has been for me over all these years ...

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Old 26th August 2012, 03:19 AM   #27008
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There is no flaw with CD, no more than any other type of sound reproduction mechanism. Frank
Frank, I'm not sure what you are attempting to say. Is it that CD is perfect, or is it that CD no more flawed than other mediums?
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Old 26th August 2012, 03:32 AM   #27009
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but with no convincing evidence that it is "clearly audible"

the 2006 3rd edition of Fastl, Zwicker Psycho-Acoustics book includes CD res demos - with no apologies or warnings for the "poor sample rate", 22.1 kHz ringing or other "digital artifacts" - does recommend headphones or very low reverberation listening room


the burden is to offer Positive results in Blinded testing - "rejecting the null hypothesis"

once we have a few positive results, accepted protocols then we can talk population statistics - does Stereophile's readership, "High End Audio" customers care if a 3rd sigma tail of prepubescent girls can tell a difference between 20 kHz and 40 kHz anti-alias/image reject filters


even the developers and their proven "highly resolving" skilled listening testers who train on the artifacts can't AB/X modern tuned psychoacoustic compression at 320k on the vast majority of musical releases - today it takes both training and selection of "killer samples" hitting the weak spots of the algorithms - algorithms that toss out 75% of the Shannon-Hartley Channel Capacity information of CD res audio

Last edited by jcx; 26th August 2012 at 03:34 AM.
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Old 26th August 2012, 03:33 AM   #27010
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Frank, I'm not sure what you are attempting to say. Is it that CD is perfect, or is it that CD no more flawed than other mediums?
All mediums are flawed, and so is CD. Just by virtue of "only" using 16 bits, and also possibly by the sampling rate if one's hearing happens to be able to go above 22kHz. But in my experience it is less flawed than other sound carrying mediums. But, I am not saying that many of implementations of CD replay are not severely flawed in key, seriously audible areas, this is an entirely different thing!

Frank
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