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#1
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Is the audio output of a CD player analog or digital?
When Hemo (Marvin Miller) insists that Dr. Science (Dr. Frank Baxter)
respond with the two words that shows he understands the essence of blood, Dr. Science comes back with "sea water". So... Here's my equivalent of the "sea water" answer. "Is the audio output of a CD player analog or digital?" It's digital. Once you've converted analog to digital, the damage is done and can't be undone. You can't go home again. Here's the explanation... Consider the classic sampling of a band-limited signal. The sampling process produces a string of pulses whose amplitudes are exactly the amplitude of the signal at the instant of sampling. Because this amplitude can vary continuously (ie, have any value, without restriction), the pulse chain is an analog signal. (analog = data representation by continuously variable values) Fourier analysis shows that the pulse train contains the original signal, unmodified. If we play the pulse train through a system free of intermodulation distortion, we will hear the original signal, unchanged. * This is true even if the system has "infinite" bandwidth, because the original signal is a component of the pulse train; no filtering is required to "recreate" it. To convert this pulse train to a digital signal, we first have to quantize its level. (I'm ignoring the use of dither, to clarify the point I'll be making. We'll consider it later.) In a 16-bit system, the signal's original amplitude range would have to be divided into 65536 equally spaced levels. ** Once the quantization is performed, the signal is digital. (digital = data representation by quantized values) Any sample can have an amplitude of only one of 65536 values. Each of these represents a "number", as assuredly as the bit settings in a two-byte register represent a "number". ("12345" is not a number; it is the representation of a number.) If you don't believe that (and of course, you don't), imagine that you had hundreds of sheets of paper with lines whose lengths were directly proportional to the quantized amplitudes, with the relative length printed next to each line. If I said I would send you the number of my street address, and you opened the envelope and found a paper with a long line on it, would you have any trouble finding the line of the matching length on the reference sheets, and determining that my condo number was 17610? I don't think so. Let's repeat the listening test. If the quantized samples are played, we'll hear the original signal, with varying amounts of quantization noise. *** Furthermore, if we converted the quantized levels to digital numbers, then reversed the process, converting those numbers back to the corresponding voltage levels, the quantization noise would still be present. In other words, there's no way to audibly distinguish a quantized pulse train with the same signal recreated from a string of "numbers" -- because there isn't any difference. The level-quantized samples and the PCM bit sequences representing them are /exactly the same numbers/. "But wait!" you say. "If you run the signal through a low-pass reconstruction filter" (which doesn't and never will exist, but we'll ignore that), "all them sharp little edges will be rounded off, and the horizontal lines will be tilted and curved, and we'll have a nice analog signal again. Right?" Wrong. The signal still contains the quantization errors, because they appear in the "baseband" component of the signal, and cannot be removed by filtering. So... How can a signal with quantization noise can be analog? (I'm waiting, Hemo.) It can't, of course. Regardless of what the waveform /looks like/, the fact is that it comprises only a finite number of signal levels. If it didn't, there wouldn't be any quantization noise. QED. The output of a CD player is digital, not analog. As for dither... It randomizes the quantization noise to minimize its audibility. But the noise is still present, because the signal does not vary in a continuous fashion. It's just that the errors have been moved around to reduce their correlation with the signal. * Other than the frequency response variation caused by the finite sampling width. ** One could have non-linear quantization. I'm ignoring that for simplicity, and because it's not often done. *** If you don't have a test CD with an undithered tone sweep, find one. It's quite interesting to hear the bursts of quantization noise as the test tone sweeps through frequencies that are submultiples of the sampling rate. Of course, there's quantization noise at _all_ frequencies. It's just that, when the test tone is not "too close" to a submultiple, the errors are sufficiently "random", particularly with musical material, not to be particularly noticeable at normal listening levels. |
#2
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Is the audio output of a CD player analog or digital?
On Mon, 19 Oct 2009 05:33:17 -0700, "William Sommerwerck"
wrote: When Hemo (Marvin Miller) insists that Dr. Science (Dr. Frank Baxter) respond with the two words that shows he understands the essence of blood, Dr. Science comes back with "sea water". So... Here's my equivalent of the "sea water" answer. "Is the audio output of a CD player analog or digital?" It's digital. Once you've converted analog to digital, the damage is done and can't be undone. You can't go home again. Here's the explanation... Consider the classic sampling of a band-limited signal. The sampling process produces a string of pulses whose amplitudes are exactly the amplitude of the signal at the instant of sampling. Because this amplitude can vary continuously (ie, have any value, without restriction), the pulse chain is an analog signal. (analog = data representation by continuously variable values) Fourier analysis shows that the pulse train contains the original signal, unmodified. If we play the pulse train through a system free of intermodulation distortion, we will hear the original signal, unchanged. * This is true even if the system has "infinite" bandwidth, because the original signal is a component of the pulse train; no filtering is required to "recreate" it. To convert this pulse train to a digital signal, we first have to quantize its level. (I'm ignoring the use of dither, to clarify the point I'll be making. We'll consider it later.) In a 16-bit system, the signal's original amplitude range would have to be divided into 65536 equally spaced levels. ** Once the quantization is performed, the signal is digital. (digital = data representation by quantized values) Any sample can have an amplitude of only one of 65536 values. Each of these represents a "number", as assuredly as the bit settings in a two-byte register represent a "number". ("12345" is not a number; it is the representation of a number.) If you don't believe that (and of course, you don't), imagine that you had hundreds of sheets of paper with lines whose lengths were directly proportional to the quantized amplitudes, with the relative length printed next to each line. If I said I would send you the number of my street address, and you opened the envelope and found a paper with a long line on it, would you have any trouble finding the line of the matching length on the reference sheets, and determining that my condo number was 17610? I don't think so. Let's repeat the listening test. If the quantized samples are played, we'll hear the original signal, with varying amounts of quantization noise. *** Furthermore, if we converted the quantized levels to digital numbers, then reversed the process, converting those numbers back to the corresponding voltage levels, the quantization noise would still be present. In other words, there's no way to audibly distinguish a quantized pulse train with the same signal recreated from a string of "numbers" -- because there isn't any difference. The level-quantized samples and the PCM bit sequences representing them are /exactly the same numbers/. "But wait!" you say. "If you run the signal through a low-pass reconstruction filter" (which doesn't and never will exist, but we'll ignore that), "all them sharp little edges will be rounded off, and the horizontal lines will be tilted and curved, and we'll have a nice analog signal again. Right?" Wrong. The signal still contains the quantization errors, because they appear in the "baseband" component of the signal, and cannot be removed by filtering. So... How can a signal with quantization noise can be analog? (I'm waiting, Hemo.) It can't, of course. Regardless of what the waveform /looks like/, the fact is that it comprises only a finite number of signal levels. If it didn't, there wouldn't be any quantization noise. QED. The output of a CD player is digital, not analog. As for dither... It randomizes the quantization noise to minimize its audibility. But the noise is still present, because the signal does not vary in a continuous fashion. It's just that the errors have been moved around to reduce their correlation with the signal. * Other than the frequency response variation caused by the finite sampling width. ** One could have non-linear quantization. I'm ignoring that for simplicity, and because it's not often done. *** If you don't have a test CD with an undithered tone sweep, find one. It's quite interesting to hear the bursts of quantization noise as the test tone sweeps through frequencies that are submultiples of the sampling rate. Of course, there's quantization noise at _all_ frequencies. It's just that, when the test tone is not "too close" to a submultiple, the errors are sufficiently "random", particularly with musical material, not to be particularly noticeable at normal listening levels. I think we have heard it all now. Meltdown is complete. Here's a little hint for you. The output of a CD player contains no discernable quantization levels. The analogue anti-alias filter following the oversampled DAC has removed every last trace of them. The signal is pure analogue. d |
#3
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Is the audio output of a CD player analog or digital?
I think we have heard it all now. Meltdown is complete.
Whose? Here's a little hint for you. The output of a CD player contains no discernable quantization levels. The analogue anti-alias filter following the oversampled DAC has removed every last trace of them. The signal is pure analogue. Quantization and aliasing are unrelated effects. My explanation spelled out the logic of this, which is plain to anyone who gives it a little thought. Why don't you think this through? Take two brains and call me in the morning. I want an apology, too, by the way. Not for disagreeing with me, but for not using your basic intelligence. I won't discuss this any further. PS: Before posting this, I asked An Internationally Famous Designer for his views. He said "it's a fine point", but agreed that what is done cannot be undone. Once you've quantized the signal, you cannot remove it the quantization error. This, as I pointed out, is shown by the fact that the quantization nose remains, even after the filtering. QED, as they say. |
#4
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Is the audio output of a CD player analog or digital?
On Mon, 19 Oct 2009 06:03:50 -0700, "William Sommerwerck"
wrote: I think we have heard it all now. Meltdown is complete. Whose? Here's a little hint for you. The output of a CD player contains no discernable quantization levels. The analogue anti-alias filter following the oversampled DAC has removed every last trace of them. The signal is pure analogue. Quantization and aliasing are unrelated effects. My explanation spelled out the logic of this, which is plain to anyone who gives it a little thought. The anti alias filter removes the quantization steps. This has nothing whatever to do with any quantization distortion products that may already have been generated during the initial A/D process. You are yet again muddling all your terminologies. Subject the output of a CD player to the closest examination you can bring to bear, and you will find no flat regions corresponding to quantization levels. Why don't you think this through? Take two brains and call me in the morning. Every digital engineer in the world (apart from you, evidently) has done all this long ago. I want an apology, too, by the way. Not for disagreeing with me, but for not using your basic intelligence. Pompous as ever. I won't discuss this any further. PS: Before posting this, I asked An Internationally Famous Designer for his views. He said "it's a fine point", but agreed that what is done cannot be undone. Once you've quantized the signal, you cannot remove it the quantization error. This, as I pointed out, is shown by the fact that the quantization nose remains, even after the filtering. QED, as they say. What have quantization errors and quantization noise to do with anything? They are artefacts of the initial process, and cannot be removed. It is the QUANTIZATION itself that is removed by the anti-alias filter. Yet again, you are having trouble working out what all the various terms mean. And by the way, argument from authority is one of the logical fallacies of the Debating Trade Tricks. You fail again. d |
#5
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Is the audio output of a CD player analog or digital?
"Don Pearce" wrote in message
I think we have heard it all now. Meltdown is complete. Agreed. I have to admit I lacked the time or stomach to read the whole tome word-for-word. The answer to the purported question said all I needed to hear. I've heard the rest from the unwashed far too many times. Here's a little hint for you. The output of a CD player contains no discernable quantization levels. True in general. I suspect that if you pay enough for one of those audiophile specials with allegedly no reconstruction filtering, traces of them might be there. The analogue anti-alias filter following the oversampled DAC has removed every last trace of them. That's how its supposed to work, and that is how it works out in almost every reasonable case. The signal is pure analogue. Well, about as pure analog as it gets in ordinary life - even many special places in life. Not being a registered meter reader like yours truly, our esteemed colleague William has missed out on some of the more instructive ironies of life. Back in the day, I built up a highly modified Heath THD analyzer that performed up to 100 times better than the best Benton Harbor chose to provide. I had a correspondingly modified audio signal generator, and the two together could get down well under 0.01% - actually 0.0025% under some conditions. Both were about as analog as it gets. I still remember the first time I hooked my lovingly-modded "pure analog" signal generator and THD analyzer up to what I would call my first serious digital audio interface - a Turtle Beach Pinnacle of Fiji if memory serves. Right up front, spectrum analysis showed that the *digital* Fiji was in general a better and purer signal source than my all-analog signal generator, and also a better and more sensitive signal analyzer than my all-analog THD analyzer. And the rest is history. A really good CD player can easily outperform "pure analog" hardware by factors of from 3 to 10 or more. The no-name, no-price audio interfaces on a typical PC motherboard can have residuals that are easily 80 to 90 dB down. The world is full of "pure analog" hardware that they can do a good job of measuring. |
#6
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Is the audio output of a CD player analog or digital?
On Mon, 19 Oct 2009 06:03:50 -0700, William Sommerwerck wrote:
Why don't you think this through? Take two brains and call me in the morning. This is the classic naive view about digital audio that has been argued countless times. Information theory at least 40 years old (and still valid) has left you way behind. Summary: Analog = signal + random noise Digital = signal + random noise (assuming it's done properly, which includes dithering) End of story. The earth is flat. It's obvious. -- Anahata ==//== 01638 720444 http://www.treewind.co.uk ==//== http://www.myspace.com/maryanahata |
#7
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Is the audio output of a CD player analog or digital?
"Since its inception, the many counter-intuitive results of quantum
mechanics have provoked strong philosophical debate and many interpretations. Even fundamental issues such as Max Born's basic rules concerning probability amplitudes and probability distributions took decades to be appreciated...." http://en.wikipedia.org/wiki/Quantum...l_consequences |
#8
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Is the audio output of a CD player analog or digital?
Arny Krueger wrote:
"Don Pearce" wrote in message Here's a little hint for you. The output of a CD player contains no discernable quantization levels. True in general. I suspect that if you pay enough for one of those audiophile specials with allegedly no reconstruction filtering, traces of them might be there. Well, there may be some ragged slopes, but that doesn't equate to quantized levels (and I don't think it would sound very good, either). The analogue anti-alias filter following the oversampled DAC has removed every last trace of them. That's how its supposed to work, and that is how it works out in almost every reasonable case. The signal is pure analogue. Well, about as pure analog as it gets in ordinary life - even many special places in life. The CD's output is an analogue of the post-DAC signal, regardless of how analogous that may be of the original source material. Best, Neil |
#9
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Is the audio output of a CD player analog or digital?
William Sommerwerck wrote:
I think we have heard it all now. Meltdown is complete. Whose? Here's a little hint for you. The output of a CD player contains no discernable quantization levels. The analogue anti-alias filter following the oversampled DAC has removed every last trace of them. The signal is pure analogue. Quantization and aliasing are unrelated effects. My explanation spelled out the logic of this, which is plain to anyone who gives it a little thought. No - bear with us. We're trying to implement a reconstruction filter. That which follows a Nyqist-conformant D/A converter will be analog, by the magic of the bandlimit part of the Nyquist theorem. snip -- Les Cargill |
#10
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Is the audio output of a CD player analog or digital?
Quantization and aliasing are unrelated effects. My explanation spelled
out the logic of this, which is plain to anyone who gives it a little thought. No - bear with us. We're trying to implement a reconstruction filter. There is no such thing. To imagine that there is only throws everything into confusion. That which follows a Nyqist-conformant D/A converter will be analog, by the magic of the bandlimit part of the Nyquist theorem. No, because the quantization errors remain within the audio band. (I tried to make this clear by "stepping through" the developmental sequence in the original explanation.) The filter cannot remove them. The other point, of course is... how can you correctly recreate discarded data? |
#11
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Is the audio output of a CD player analog or digital?
"Don Pearce" wrote in message
... The anti alias filter removes the quantization steps. Of course it does not!! Let's simplify the system William describes to a one bit system, sampling at 2 kHz. If you put a 1kHz sinewave in, you get a square wave in the digital domain, which will be a sinewave again after the D/A conversion and filtering, simply because the filter removes anything above 2kHz. So indeed, you won't be able to measure any quantisation on the output, *as long as you put this sine wave in*. Now, lower the input fequency to, say, 1Hz. Et voila, on the output appears a square wave with rounded edges... Now you can clearly observe that this system can only represent two stable levels. The only thing an anti alias filter does is smooth the transitions between quantization steps. Meindert |
#12
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Is the audio output of a CD player analog or digital?
On Tue, 20 Oct 2009 09:13:27 +0200, "Meindert Sprang"
wrote: "Don Pearce" wrote in message ... The anti alias filter removes the quantization steps. Of course it does not!! Let's simplify the system William describes to a one bit system, sampling at 2 kHz. If you put a 1kHz sinewave in, you get a square wave in the digital domain, which will be a sinewave again after the D/A conversion and filtering, simply because the filter removes anything above 2kHz. So indeed, you won't be able to measure any quantisation on the output, *as long as you put this sine wave in*. Now, lower the input fequency to, say, 1Hz. Et voila, on the output appears a square wave with rounded edges... Now you can clearly observe that this system can only represent two stable levels. The only thing an anti alias filter does is smooth the transitions between quantization steps. Meindert No. Simple as that. Do you seriously think that at 1Hz, you would get out a level corresponding to a quantization step? You don't. You get the right level, intermediate between two quantization steps. That is what dither does, and that is why it is an integral and necessary part of the encoding process. I'll ignore the first part of your comment, where you have failed to understand how the Nyquist condition works. Anti-alias filtering too for that matter. In fact, why did you post this at all? The whole thing is just gibberish. d |
#13
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Is the audio output of a CD player analog or digital?
"Don Pearce" wrote in message
... No. Simple as that. Do you seriously think that at 1Hz, you would get out a level corresponding to a quantization step? You don't. You get the right level, intermediate between two quantization steps. That is what dither does, and that is why it is an integral and necessary part of the encoding process. The system William described, had no dithering. Neither had my simplification of that system. Your remark that an anti alias filter removes the quantization steps is only partially true. It only does when the digital signal was dithered. I'll ignore the first part of your comment, where you have failed to understand how the Nyquist condition works. Anti-alias filtering too for that matter. That is probably why my customers are so happy with the DSP systems I designed for them... Meindert |
#14
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Is the audio output of a CD player analog or digital?
On Tue, 20 Oct 2009 09:49:37 +0200, "Meindert Sprang"
wrote: "Don Pearce" wrote in message ... No. Simple as that. Do you seriously think that at 1Hz, you would get out a level corresponding to a quantization step? You don't. You get the right level, intermediate between two quantization steps. That is what dither does, and that is why it is an integral and necessary part of the encoding process. The system William described, had no dithering. Neither had my simplification of that system. It is not a simplified system, it is a broken system. And even without dither you still won't find any quantization steps. They will only be evident in the sloping parts of the waveform, but you won't find them. They will have been filtered away. Your remark that an anti alias filter removes the quantization steps is only partially true. It only does when the digital signal was dithered. I'll ignore the first part of your comment, where you have failed to understand how the Nyquist condition works. Anti-alias filtering too for that matter. That is probably why my customers are so happy with the DSP systems I designed for them... Meindert Oh god, not another one. Do read your own post, will you? Review your numbers and claims. d |
#15
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Is the audio output of a CD player analog or digital?
"Don Pearce" wrote in message
... On Tue, 20 Oct 2009 09:49:37 +0200, "Meindert Sprang" wrote: "Don Pearce" wrote in message ... No. Simple as that. Do you seriously think that at 1Hz, you would get out a level corresponding to a quantization step? You don't. You get the right level, intermediate between two quantization steps. That is what dither does, and that is why it is an integral and necessary part of the encoding process. The system William described, had no dithering. Neither had my simplification of that system. It is not a simplified system, it is a broken system. Why? Because it proves you wrong? Meindert |
#16
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Is the audio output of a CD player analog or digital?
On Tue, 20 Oct 2009 10:16:02 +0200, "Meindert Sprang"
wrote: "Don Pearce" wrote in message ... On Tue, 20 Oct 2009 09:49:37 +0200, "Meindert Sprang" wrote: "Don Pearce" wrote in message ... No. Simple as that. Do you seriously think that at 1Hz, you would get out a level corresponding to a quantization step? You don't. You get the right level, intermediate between two quantization steps. That is what dither does, and that is why it is an integral and necessary part of the encoding process. The system William described, had no dithering. Neither had my simplification of that system. It is not a simplified system, it is a broken system. Why? Because it proves you wrong? Meindert You snip the reasoning. That marks the end of this conversation as I do not intend to repeat it to a dishonest man. d |
#17
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Is the audio output of a CD player analog or digital?
"Don Pearce" wrote in message
... You snip the reasoning. That marks the end of this conversation as I do not intend to repeat it to a dishonest man. Don, I am a self-taught professional who makes his living from designing hardware, software and emdedded systems and I have a strong interest in music. I may not be up to speed with everything I need to know but I am always willing to learn new things. But I also recognize my knowlegde based on my experience. For instance, if someone throws a fourier transform at me in pure mathematical form, I bail out. But if I see an FFT algorithm explained in diagams with bit reversals and twiddle factors, I am perfectly capable of understanding what happens and I can implement the algorithm. But one thing I am very, very sure of: I am not dishonest! Meindert |
#18
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Is the audio output of a CD player analog or digital?
No, because the quantization errors remain within the audio band.
(I tried to make this clear by "stepping through" the developmental sequence in the original explanation.) The filter cannot remove them. Demonstrate those errors. Show them "stepping through". Do it on the test bench. Your conjecture is testable. That should be inarguable. Ever heard of a thought experiment? The other point, of course is... how can you correctly recreate discarded data? You're asking this in the context of a world where 192 KHz AD's are becoming much more common? You hear much over 90+ KHz or so? Digital recording and playback have been commonplace for a quarter century. Yet people -- recording engineers! -- still don't understand the difference between time sampling and quantization! This is beyond my comprehension. Isn't there anyone out there with the least understanding of how digital recording and playback actually work? |
#19
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Is the audio output of a CD player analog or digital?
The anti alias filter removes the quantization steps.
Of course it does not!! Let's simplify the system William describes to a one bit system, sampling at 2 kHz. If you put a 1kHz sinewave in, you get a square wave in the digital domain, which will be a sinewave again after the D/A conversion and filtering, simply because the filter removes anything above 2kHz. So indeed, you won't be able to measure any quantisation on the output, *as long as you put this sine wave in*. Now, lower the input fequency to, say, 1Hz. Et voila, on the output appears a square wave with rounded edges... Now you can clearly observe that this system can only represent two stable levels. The only thing an anti alias filter does is smooth the transitions between quantization steps. Thank you. I'm not surprised that support come from a fellow German. We're very logical people. |
#20
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Is the audio output of a CD player analog or digital?
"William Sommerwerck" wrote in message
... The anti alias filter removes the quantization steps. Of course it does not!! Let's simplify the system William describes to a one bit system, sampling at 2 kHz. If you put a 1kHz sinewave in, you get a square wave in the digital domain, which will be a sinewave again after the D/A conversion and filtering, simply because the filter removes anything above 2kHz. So indeed, you won't be able to measure any quantisation on the output, *as long as you put this sine wave in*. Now, lower the input fequency to, say, 1Hz. Et voila, on the output appears a square wave with rounded edges... Now you can clearly observe that this system can only represent two stable levels. The only thing an anti alias filter does is smooth the transitions between quantization steps. Thank you. I'm not surprised that support come from a fellow German. We're very logical people. Close. I'm Dutch :-) Meindert |
#21
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Is the audio output of a CD player analog or digital?
On Tue, 20 Oct 2009 04:45:24 -0700, "William Sommerwerck"
wrote: The anti alias filter removes the quantization steps. Of course it does not!! Let's simplify the system William describes to a one bit system, sampling at 2 kHz. If you put a 1kHz sinewave in, you get a square wave in the digital domain, which will be a sinewave again after the D/A conversion and filtering, simply because the filter removes anything above 2kHz. So indeed, you won't be able to measure any quantisation on the output, *as long as you put this sine wave in*. Now, lower the input fequency to, say, 1Hz. Et voila, on the output appears a square wave with rounded edges... Now you can clearly observe that this system can only represent two stable levels. The only thing an anti alias filter does is smooth the transitions between quantization steps. Thank you. I'm not surprised that support come from a fellow German. We're very logical people. So that is two Germans happy with the idea that you can not only sample a 1kHz sine wave at 2kHz, but also perform the anti alias filtering at 2kHz. And to think they had ambitions to rule the world. d |
#22
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Is the audio output of a CD player analog or digital?
"Don Pearce" wrote in message
... So that is two Germans happy with the idea that you can not only sample a 1kHz sine wave at 2kHz, but also perform the anti alias filtering at 2kHz. And to think they had ambitions to rule the world. Oops, typo. The filter was supposed to be at 1kHz.... Meindert |
#23
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Is the audio output of a CD player analog or digital?
On Tue, 20 Oct 2009 13:56:13 +0200, "Meindert Sprang"
wrote: "Don Pearce" wrote in message ... So that is two Germans happy with the idea that you can not only sample a 1kHz sine wave at 2kHz, but also perform the anti alias filtering at 2kHz. And to think they had ambitions to rule the world. Oops, typo. The filter was supposed to be at 1kHz.... Meindert And the sampling? d |
#24
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Is the audio output of a CD player analog or digital?
"Don Pearce" wrote in message
... On Tue, 20 Oct 2009 13:56:13 +0200, "Meindert Sprang" wrote: "Don Pearce" wrote in message ... So that is two Germans happy with the idea that you can not only sample a 1kHz sine wave at 2kHz, but also perform the anti alias filtering at 2kHz. And to think they had ambitions to rule the world. Oops, typo. The filter was supposed to be at 1kHz.... Meindert And the sampling? 2kHz. Meindert |
#25
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Is the audio output of a CD player analog or digital?
On Tue, 20 Oct 2009 13:59:00 +0200, "Meindert Sprang"
wrote: "Don Pearce" wrote in message ... On Tue, 20 Oct 2009 13:56:13 +0200, "Meindert Sprang" wrote: "Don Pearce" wrote in message ... So that is two Germans happy with the idea that you can not only sample a 1kHz sine wave at 2kHz, but also perform the anti alias filtering at 2kHz. And to think they had ambitions to rule the world. Oops, typo. The filter was supposed to be at 1kHz.... Meindert And the sampling? 2kHz. Ok, so you don't understand one of the most basic rules of sampling. d |
#26
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Is the audio output of a CD player analog or digital?
"Don Pearce" wrote in message
... On Tue, 20 Oct 2009 13:59:00 +0200, "Meindert Sprang" wrote: "Don Pearce" wrote in message ... On Tue, 20 Oct 2009 13:56:13 +0200, "Meindert Sprang" wrote: "Don Pearce" wrote in message ... So that is two Germans happy with the idea that you can not only sample a 1kHz sine wave at 2kHz, but also perform the anti alias filtering at 2kHz. And to think they had ambitions to rule the world. Oops, typo. The filter was supposed to be at 1kHz.... Meindert And the sampling? 2kHz. Ok, so you don't understand one of the most basic rules of sampling. d Which is, according to you? M. |
#27
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Is the audio output of a CD player analog or digital?
On Tue, 20 Oct 2009 14:03:48 +0200, "Meindert Sprang"
wrote: "Don Pearce" wrote in message ... On Tue, 20 Oct 2009 13:59:00 +0200, "Meindert Sprang" wrote: "Don Pearce" wrote in message ... On Tue, 20 Oct 2009 13:56:13 +0200, "Meindert Sprang" wrote: "Don Pearce" wrote in message ... So that is two Germans happy with the idea that you can not only sample a 1kHz sine wave at 2kHz, but also perform the anti alias filtering at 2kHz. And to think they had ambitions to rule the world. Oops, typo. The filter was supposed to be at 1kHz.... Meindert And the sampling? 2kHz. Ok, so you don't understand one of the most basic rules of sampling. d Which is, according to you? M. You can not sample a 1kHz signal at 2kHz. According to me, of course. You clearly know better. d |
#28
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Is the audio output of a CD player analog or digital?
"Don Pearce" wrote in message
... You can not sample a 1kHz signal at 2kHz. According to me, of course. You clearly know better. According to Nyquist you can. You even mentioned that yourself earlier.... M. |
#29
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Is the audio output of a CD player analog or digital?
On Tue, 20 Oct 2009 14:12:39 +0200, "Meindert Sprang"
wrote: "Don Pearce" wrote in message ... You can not sample a 1kHz signal at 2kHz. According to me, of course. You clearly know better. According to Nyquist you can. You even mentioned that yourself earlier.... No, Nyquist never said any such thing. Go back to the books. Have you truly done A/D design? It is sounding less likely with your every post. d |
#30
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Is the audio output of a CD player analog or digital?
That which follows a Nyquist-conformant D/A converter
will be analog, by the magic of the bandlimit part of the Nyquist theorem. No, because the quantization errors remain within the audio band. Not according to all the constraints of the Nyquist Theorem. They're *out* of band, except for least-[significant-]bit errors which are masked by dithering. That's the point... Dithering doesn't mask quantization errors. It simply moves them around to make them more like random noise. Furthermore, what makes digital "digital" is quantization error. If there were no quantization error (an impossibility), signal values would be able to vary continuously, and you would have an analog signal. The direct output of a DAC (prior to any filtering) is always representable by a finite number of voltage levels. It is therefore digitial. It reproduces the quantization errors (dithered or not) of the original sampling process. No amount of filtering can change this. True, you can use oversampling and other techniques to move part of the quantization error into the ultrasonic region, thus gaining resolution in the audible band. But you can never move all of it. And as long as you have quantization error, you have a digital signal. QED. What is so difficult to understand about this? Don't you understand doors? Ready your gum wrappers, people. The secrets of the universe are written thereon. |
#31
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Is the audio output of a CD player analog or digital?
Thank you. I'm not surprised that support come from
a fellow German. We're very logical people. Close. I'm Dutch :-) Close enough. I've been told I must be of Dutch extraction because my name is spelled with a "c". But my family came from Hildesheim. |
#32
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Is the audio output of a CD player analog or digital?
You can not sample a 1kHz signal at 2kHz. According to me,
of course. You clearly know better. I hate taking Mr. Pearce's side in this, but he's correct. A 1kHz signal sampled at 2kHz would "alias" to a DC signal. It's interesting that the Wikipedia article points out that the original statement of the Nyquist theorem is incorrect, as it states that sampling at twice the rate of the highest frequency is sufficient. |
#33
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Is the audio output of a CD player analog or digital?
"Don Pearce" wrote in message
... On Tue, 20 Oct 2009 14:12:39 +0200, "Meindert Sprang" wrote: "Don Pearce" wrote in message ... You can not sample a 1kHz signal at 2kHz. According to me, of course. You clearly know better. According to Nyquist you can. You even mentioned that yourself earlier.... No, Nyquist never said any such thing. Go back to the books. Sigh.... you're splitting hair now. Does Nyquist-Shannon Sampling Theorem sound better? Have you truly done A/D design? It is sounding less likely with your every post. Yes I have. Three major players in the anti-shoplifting industry used my A/D-DSP designs, I've designed a few image sampling and processing systems, a few RF signal generators using DDS, done some FFT processing and digital filtering on various DSP's (Analog Devices, Motorola). Want some schematics, PCB layouts or source code too? Meindert |
#34
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Is the audio output of a CD player analog or digital?
A 1kHz signal sampled at 2kHz would "alias" to a DC signal.
Whoops. I goofed. You'd get a kind of "sawtooth" whose amplitude was not properly defined, varying from 0 to the peak signal level, according to the relative phase of the sampling. |
#35
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Is the audio output of a CD player analog or digital?
"William Sommerwerck" wrote in message
... You can not sample a 1kHz signal at 2kHz. According to me, of course. You clearly know better. I hate taking Mr. Pearce's side in this, but he's correct. A 1kHz signal sampled at 2kHz would "alias" to a DC signal. No it doesn't. Only when the samping occurs at the zero crossings, you end up with DC, 0V to be precisely. At any other point in time, you end up with samples of exactly the same voltage, anywhere between 0V and the peak voltage of the signal, but with alternating signs, aka a digital squarewave. If you look at it mathematically, sampling 1kHz with 2kHz is the same as adding and subtracting both frequencies, resulting in 1kHz and 3kHz. (2+1 and 2-1). Sampling 1kHz with 1kHz does indeed result in DC and 2kHz. Meindert |
#36
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Is the audio output of a CD player analog or digital?
"Meindert Sprang" wrote in
message "Don Pearce" wrote in message ... The anti alias filter removes the quantization steps. Of course it does not!! Let's simplify the system William describes to a one bit system, sampling at 2 kHz. If you put a 1kHz sinewave in, you get a square wave in the digital domain, which will be a sinewave again after the D/A conversion and filtering, simply because the filter removes anything above 2kHz. So indeed, you won't be able to measure any quantisation on the output, *as long as you put this sine wave in*. Now, lower the input fequency to, say, 1Hz. Et voila, on the output appears a square wave with rounded edges... Now you can clearly observe that this system can only represent two stable levels. I see we have a purported factual claim from someone who has obviously never actually done the experiment whose results they purport to present. If you actually look at (with an oscilliscope using an expanded scale) or measure a 1 Hz wave coming out of a CD player with enough LF bandpass to actually produce a signficantly large 1 Hz wave, you will find no such square wave, or any evidence of stairstepping. I've done both the examination with a scope and also a detailed spectral analysis. No significant stair steps, no square waves, nada. Just tiny residuals if anything at all. The reason for this is that if the stairstepping were present, its frequency would be at half the sampling frequency (Nyquist) and/or harmonics thereof the first of which is the sampling frequency. However, frequencies of Nyquist or above are attenuated very many dB by the reconstruction filter. Only tiny traces of them might be found, if they are measurable at all. |
#37
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Is the audio output of a CD player analog or digital?
Of course it does not!!
Let's simplify the system William describes to a one bit system, sampling at 2 kHz. If you put a 1kHz sinewave in, you get a square wave in the digital domain, which will be a sinewave again after the D/A conversion and filtering, simply because the filter removes anything above 2kHz. So indeed, you won't be able to measure any quantisation on the output, *as long as you put this sine wave in*. Now, lower the input fequency to, say, 1Hz. Et voila, on the output appears a square wave with rounded edges... Now you can clearly observe that this system can only represent two stable levels. I see we have a purported factual claim from someone who has obviously never actually done the experiment whose results they purport to present. If you actually look at (with an oscilliscope using an expanded scale) or measure a 1 Hz wave coming out of a CD player with enough LF bandpass to actually produce a signficantly large 1 Hz wave, you will find no such square wave, or any evidence of stairstepping. I've done both the examination with a scope and also a detailed spectral analysis. No significant stair steps, no square waves, nada. Just tiny residuals if anything at all. The reason for this is that if the stairstepping were present, its frequency would be at half the sampling frequency (Nyquist) and/or harmonics thereof the first of which is the sampling frequency. However, frequencies of Nyquist or above are attenuated very many dB by the reconstruction filter. Only tiny traces of them might be found, if they are measurable at all. I won't gainsay your experiment or observations. However, as long as quantization noise is present in the output, the signal is digital. Please see my other post. "Think, people, think!" |
#38
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Is the audio output of a CD player analog or digital?
On Tue, 20 Oct 2009 06:02:05 -0700, "William Sommerwerck"
wrote: I won't gainsay your experiment or observations. However, as long as quantization noise is present in the output, the signal is digital. Please see my other post. Quantization noise is a distortion produced by a modulation process. Once the distortion is there, there is no way to remove it. Although that energy can not be prevented, it can be spread out into wideband noise by dithering, which is audibly preferable. But that is all it is - some distortion. There is nothing magical about it that converts an analogue signal into a digital one. Once the signal is out of the DAC, and filed smooth by oversampling and filtering you have an analogue signal that is just a tiny bit distorted. There are no steps, no digits, Just signal plus noise and distortion. d |
#39
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Is the audio output of a CD player analog or digital?
"William Sommerwerck" wrote in
message Of course it does not!! Let's simplify the system William describes to a one bit system, sampling at 2 kHz. If you put a 1kHz sinewave in, you get a square wave in the digital domain, which will be a sinewave again after the D/A conversion and filtering, simply because the filter removes anything above 2kHz. So indeed, you won't be able to measure any quantisation on the output, *as long as you put this sine wave in*. Now, lower the input fequency to, say, 1Hz. Et voila, on the output appears a square wave with rounded edges... Now you can clearly observe that this system can only represent two stable levels. I see we have a purported factual claim from someone who has obviously never actually done the experiment whose results they purport to present. If you actually look at (with an oscilliscope using an expanded scale) or measure a 1 Hz wave coming out of a CD player with enough LF bandpass to actually produce a signficantly large 1 Hz wave, you will find no such square wave, or any evidence of stairstepping. I've done both the examination with a scope and also a detailed spectral analysis. No significant stair steps, no square waves, nada. Just tiny residuals if anything at all. The reason for this is that if the stairstepping were present, its frequency would be at half the sampling frequency (Nyquist) and/or harmonics thereof the first of which is the sampling frequency. However, frequencies of Nyquist or above are attenuated very many dB by the reconstruction filter. Only tiny traces of them might be found, if they are measurable at all. I won't gainsay your experiment or observations. However, as long as quantization noise is present in the output, the signal is digital. No, its just a signal with some noise just like any real world analog signal. Any proper digital system is dithered, and the purpose of dither is to modify quantization noise so that it has a pseudo-randomized spectrum. Therefore, the actual quantization noise that one finds at the output of a well-designed CD player (and almost all are well-enough designed to pass this test) will be indistingushable from the usual residual noise you find in any real world analog system. The actual responsibility for dithering CDs is with the people who produce the CD recording. The player is just the messenger. The good news is that this means that any enhancments to the dithering process can benefit the users of all properly-designed players. |
#40
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Is the audio output of a CD player analog or digital?
"Don Pearce" wrote in message
On Tue, 20 Oct 2009 06:02:05 -0700, "William Sommerwerck" wrote: I won't gainsay your experiment or observations. However, as long as quantization noise is present in the output, the signal is digital. Please see my other post. Quantization noise is a distortion produced by a modulation process. Right, and since any proper digital process is dithered, the actual quantization noise at its output will strongly resemble the usual noise that we find in real-world analog systems. Once the distortion is there, there is no way to remove it. Although that energy can not be prevented, it can be spread out into wideband noise by dithering, which is audibly preferable. Not only is dither preferable, it is a *requirement* for proper digitization. But that is all it is - some distortion. There is nothing magical about it that converts an analogue signal into a digital one. Once the signal is out of the DAC, and filed smooth by oversampling and filtering you have an analogue signal that is just a tiny bit distorted. There are no steps, no digits, Just signal plus noise and distortion. Actually, properly dithered signals just have what appears to be a noise floor. The noise may be pseudo-random and in some sense predictable, but if you dither with a truely random noise source, the noise floor at the output will be truely random. |
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