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"Audiophile" listening event @ Definitive Audio in Seattle, Atkinson to demonstrate "evils of MP3"
2Bdecided
post Mar 2 2011, 14:51
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QUOTE (Arnold B. Krueger @ Mar 2 2011, 12:26) *
QUOTE (2Bdecided @ Mar 2 2011, 06:49) *
QUOTE (Stereoeditor @ Mar 1 2011, 18:46) *
That some (but not all, of course) 24-bit recordings do have signal-related content in the 8 LSBs I thought interesting, given that many people have written that all real-world recordings will have sufficiently high a noise floor to randomize the LSBs below the 16th.


I see - I agree that this is interesting for that reason. Do you recall any examples?

Virtually *every* real world recording has "signal-related content" whose amplitude is less than 16 bits
...I'm sure there's "signal related content" down to the molecular level in the original room, and I'm sure various combinations of microphones and electronics beat 16-bits in some respects.

That's not the point. The claim is that those 8 LSBs of a 24-bit recording contain something that isn't random, and that this "not randomised" nature was demonstrated by listening to them (if I'm following this correctly - I could be wrong!).

I've listened to lots of groups of LSBs on their own, and you rarely hear anything other than white noise. It depends on how many LSBs, the original bitdepth, and the signal itself of course - but it would still be interesting to know of 24-bit recordings where you hear something other than white noise, because all the ones I've checked (which aren't synthetic, and don't have artificial fade-outs or reverb) just give white noise. I can imagine there may be some which don't quite sound like white noise, and if so, I'd be interested to find them.

Please don't read any more into it than that.

Cheers,
David.
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Arnold B. Kruege...
post Mar 2 2011, 15:13
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QUOTE (2Bdecided @ Mar 2 2011, 08:51) *
QUOTE (Arnold B. Krueger @ Mar 2 2011, 12:26) *
QUOTE (2Bdecided @ Mar 2 2011, 06:49) *
QUOTE (Stereoeditor @ Mar 1 2011, 18:46) *
That some (but not all, of course) 24-bit recordings do have signal-related content in the 8 LSBs I thought interesting, given that many people have written that all real-world recordings will have sufficiently high a noise floor to randomize the LSBs below the 16th.


I see - I agree that this is interesting for that reason. Do you recall any examples?

Virtually *every* real world recording has "signal-related content" whose amplitude is less than 16 bits
...I'm sure there's "signal related content" down to the molecular level in the original room, and I'm sure various combinations of microphones and electronics beat 16-bits in some respects.

That's not the point. The claim is that those 8 LSBs of a 24-bit recording contain something that isn't random, and that this "not randomised" nature was demonstrated by listening to them (if I'm following this correctly - I could be wrong!).

I've listened to lots of groups of LSBs on their own, and you rarely hear anything other than white noise. It depends on how many LSBs, the original bitdepth, and the signal itself of course - but it would still be interesting to know of 24-bit recordings where you hear something other than white noise, because all the ones I've checked (which aren't synthetic, and don't have artificial fade-outs or reverb) just give white noise. I can imagine there may be some which don't quite sound like white noise, and if so, I'd be interested to find them.

Please don't read any more into it than that.


Now that you've explained what you are doing, I think I can explain your results.

As I read it, you've been stripping off the low order bits of recordings, at points where the amplitude of the recording is greater than just the bits you are stripping off. For example there may be a portion of a 24 bit integer audio track whole amplitude at some point is say the 16 low order bits. You've been stripping off lets say the 6 lowest order bits. The results are white noise. I find that to be completely predictable because of what you're doing, not necessarily due to the content of the audio track. What you are hearing is rather massive quantization noise because of the odd kind of requantizing that you are doing, and also because whatever kind of re-quantizing you are doing, you're not randomizing the quantization error.

One of the things I've learned is that low level detail is not restricted to the low order bits.

For example, lets take a test tone composed of a high amplitude signal (-6 dB FS) at 1 KHz, and a very low amplitude signal
at 500 Hz (-60 dB FS).

The question is which bits contain the low level signal. The answer is that all of the bits that represent the -6 dB FS signal are altered by the presence of the -60 dB signal. If you want to hear the -60 dB signal, you need to listen to far more than just however many few low order bits. You need to listen to *all* of the bits that are affected by the -6 dB FS signal in order to hear the -60 dB FS signal.

Now If I've misjudged your situation, my apologies, but I'm just trying to read what you write and understand it, and share my experience with this sort of thing.
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Notat
post Mar 2 2011, 15:56
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Sounds like David's essentially doing an Atkinson style difference test between 24-bit and truncated 16-bit version of the same recording. He wants to see if anything is lost by this data reduction. I think it is interesting and non-intuitive that he hasn't found anything. Especially so considering this difference process does not dither properly.
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Notat
post Mar 2 2011, 16:07
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QUOTE (Arnold B. Krueger @ Mar 1 2011, 20:27) *
QUOTE (Notat @ Mar 1 2011, 14:46) *
In high-end audio, it's all about perception. You can change what people perceive by changing their expectations. It's all in their head but that's where perception happens; they really are hearing something different.


A perception that contradicts actuality, such as the false vision of a shimmering lake in the desert, is of course called an illusion.

This is why I say that high end audiophiles who hear changes in their sighted evaluations when there is no actual change are illusional, not delusional.

Their perceptions are similar to those of normal human beings under the same conditions. There is no pathology in their perceptions of sonic differences, given the circumstances.

ABXers can and do perceive non-existent differences when they do sighted evaluations. It's just that we've evolved our means for doing comparisons in the interest of behaving more consistently with actuality.

Do audiophiles accept actuality as a useful concept?
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2Bdecided
post Mar 2 2011, 17:18
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QUOTE (Notat @ Mar 2 2011, 14:56) *
Sounds like David's essentially doing an Atkinson style difference test between 24-bit and truncated 16-bit version of the same recording. He wants to see if anything is lost by this data reduction. I think it is interesting and non-intuitive that he hasn't found anything. Especially so considering this difference process does not dither properly.
Yes, exactly. I'd imagine there may be recordings where you find something, which is why I'm interested to know which ones they are, if they exist.


On a separate topic, the difference signal due to lossyWAV's basic undithered no-noise-shaping truncation is always something like blocks of white noise. In the case of a couple of pure tones, it wouldn't remove any bits at all - it sees a -xxdB noise floor beyond the tones and leaves well alone.

lossyWAV sometimes wants to keep more than 16-bits though.

Cheers,
David.

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Stereoeditor
post Mar 2 2011, 19:26
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QUOTE (2Bdecided @ Mar 2 2011, 08:51) *
QUOTE (Arnold B. Krueger @ Mar 2 2011, 12:26) *
I'm sure there's "signal related content" down to the molecular level in the original room, and I'm sure various combinations of microphones and electronics beat 16-bits in some respects.


That's not the point. The claim is that those 8 LSBs of a 24-bit recording contain something that isn't random, and that this "not randomised" nature was demonstrated by listening to them (if I'm following this correctly - I could be wrong!).


As I said in an earlier posting, I didn't comment in my AES presentation on the audibility of what was happening in bits 17-24, only that while there was often random bit activity, with some recordings there was some signal-correlated activity in the 8 LSBs.

John Atkinson
Editor, Stereophile

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Stereoeditor
post Mar 2 2011, 19:33
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QUOTE (Ed Seedhouse @ Mar 2 2011, 01:09) *
QUOTE (Stereoeditor @ Feb 28 2011, 13:58) *
But playing the difference signal emphasizes that _something_ is removed by lossy codecs, which is a point that I also wanted to make.


But since it is a lossy codecs then by _definition_ "something" is removed. Otherwise it wouldn't be a "lossy codecs".


Of course, and I expect that point is obvious to all on HA. But to the public at large, who have been told that even low-bit-rate satellite radio is "CD quality," the difference between lossless and lossy bit-rate reduction is not as clear as you might expect. To judge by some of the emails I receive, that difference isn't even as clear as I would expect among Stereophile's readership. That was the point I was making.

John Atkinson
Editor, Stereophile
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Arnold B. Kruege...
post Mar 2 2011, 23:50
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QUOTE (Notat @ Mar 2 2011, 10:07) *
QUOTE (Arnold B. Krueger @ Mar 1 2011, 20:27) *
QUOTE (Notat @ Mar 1 2011, 14:46) *
In high-end audio, it's all about perception. You can change what people perceive by changing their expectations. It's all in their head but that's where perception happens; they really are hearing something different.


A perception that contradicts actuality, such as the false vision of a shimmering lake in the desert, is of course called an illusion.

This is why I say that high end audiophiles who hear changes in their sighted evaluations when there is no actual change are illusional, not delusional.

Their perceptions are similar to those of normal human beings under the same conditions. There is no pathology in their perceptions of sonic differences, given the circumstances.

ABXers can and do perceive non-existent differences when they do sighted evaluations. It's just that we've evolved our means for doing comparisons in the interest of behaving more consistently with actuality.

Do audiophiles accept actuality as a useful concept?


The tragedy is that this is an interesting question.
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Arnold B. Kruege...
post Mar 3 2011, 00:04
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QUOTE (2Bdecided @ Mar 2 2011, 11:18) *
QUOTE (Notat @ Mar 2 2011, 14:56) *
Sounds like David's essentially doing an Atkinson style difference test between 24-bit and truncated 16-bit version of the same recording. He wants to see if anything is lost by this data reduction. I think it is interesting and non-intuitive that he hasn't found anything. Especially so considering this difference process does not dither properly.
Yes, exactly. I'd imagine there may be recordings where you find something, which is why I'm interested to know which ones they are, if they exist.


One non-intutive thing about what you are actually testing, is that the 16 bit version can reproduce signals whose peak amplitude is << 1 (16 bit) LSB.

So, when you take the difference of these two signals, you're cancelling out a great deal of musical information whose amplifude is << 1 (16 bit) LSB. That is one explanation why all you get is noise.
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krabapple
post Mar 3 2011, 08:19
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QUOTE (2Bdecided @ Mar 1 2011, 08:22) *
It's fine to use lossless.

It doesn't mean mp3 is evil though - or necessarily audibly inferior.



Mr. Atkinson:
this is all you ever have to say in your 'dems', to tell the complete truth most efficiently.
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krabapple
post Mar 3 2011, 08:27
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QUOTE (Stereoeditor)
Of course, and I expect that point is obvious to all on HA. But to the public at large, who have been told that even low-bit-rate satellite radio is "CD quality," the difference between lossless and lossy bit-rate reduction is not as clear as you might expect. To judge by some of the emails I receive, that difference isn't even as clear as I would expect among Stereophile's readership. That was the point I was making.

John Atkinson
Editor, Stereophile



But to then NOT tell the public at large (or at least, the sample in the room with you, or in your letters column ) that detection of audible difference between lossy and lossless is not necessarily predictable from the difference signal, would be disingenuous at best. So I'm sure you make a point of mentioning that. Right? Because you're interesting in educating the public, right?



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2Bdecided
post Mar 3 2011, 11:46
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QUOTE (Arnold B. Krueger @ Mar 2 2011, 23:04) *
One non-intutive thing about what you are actually testing, is that the 16 bit version can reproduce signals whose peak amplitude is << 1 (16 bit) LSB.

So, when you take the difference of these two signals, you're cancelling out a great deal of musical information whose amplifude is << 1 (16 bit) LSB. That is one explanation why all you get is noise.
I think we're going around in circles here. Of course if it's correctly dithered the difference is noise - that's the whole point of dither.

Forget dither. Forget 16-bits. Forget what's audible. Forget everything!

1) Take a 24-bit recording. Play only the 8 LSBs, shifted into the 8 MSBs so you can hear them. What do they sound like?

2) In comparison, take a 16-bit recording. Play only the 8 LSBs, shifted into the 8 MSB to match the above. What do they sound like?

IME 1) = always white noise, 2) = sometimes white noise, but sometimes distorted mess with something vaguely related to the original signal clearly audible.

Cheers,
David.
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2Bdecided
post Mar 3 2011, 11:57
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QUOTE (Stereoeditor @ Mar 2 2011, 18:26) *
As I said in an earlier posting, I didn't comment in my AES presentation on the audibility of what was happening in bits 17-24, only that while there was often random bit activity, with some recordings there was some signal-correlated activity in the 8 LSBs.
What do you mean? I'm not trying to argue or nitpick - but honestly, what do you mean by this?

I know what "signal-correlated" means, but it's not immediately obvious to me how you make this judgement in this case.

I can easily give examples where there is (specific synthetic signals), and where there isn't (a 16-bit recording with 8 bits of noise added) - but I'm interested to know how you can even begin to make this call if I give you a 24-bit recording from an unknown source.


If we were talking about dither, and whether a specific type (or lack of) dither left signal-correlated distortion due to word length reduction, then there would be at least three things we could fall back on:
1) Mathematical proof of what the dither+quantisation does to the signal.
2) Processing of test signals and using a) waveform and/or b) spectral analysis on the results.
3) Listening - to a) the result and/or b) the difference signal
OK - I cheated - that's actually five things. Only (1) is actually conclusive, but (2a+b) and (3a+b) can still be good indicators or at least demonstrators.

I can't see how you can perform (1) for a given 24-bit recording. We can try 2 and 3 though.

Cheers,
David.
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Arnold B. Kruege...
post Mar 3 2011, 13:42
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QUOTE (2Bdecided @ Mar 3 2011, 05:46) *
QUOTE (Arnold B. Krueger @ Mar 2 2011, 23:04) *
One non-intutive thing about what you are actually testing, is that the 16 bit version can reproduce signals whose peak amplitude is << 1 (16 bit) LSB.

So, when you take the difference of these two signals, you're canceling out a great deal of musical information whose amplified is << 1 (16 bit) LSB. That is one explanation why all you get is noise.



One good one explanation is all that is needed!

QUOTE
I think we're going around in circles here.


Not me. I've got one good explanation that is relevant and correct.

QUOTE
Of course if it's correctly dithered the difference is noise - that's the whole point of dither.


So why tie yourself in knots and leave reason and logic behind?

QUOTE
Forget dither.


Seems illogical to me.

QUOTE
Forget 16-bits. Forget what's audible. Forget everything!


Now, we would appear to be in Atkinson territory - Fantasy Land! ;-)

QUOTE
1) Take a 24-bit recording. Play only the 8 LSBs, shifted into the 8 MSBs so you can hear them. What do they sound like?


That depends on whether there was data in the 16 MSBs that you threw away. If there was data there, than you hear the result of clipping. You have a mess.

QUOTE
2) In comparison, take a 16-bit recording. Play only the 8 LSBs, shifted into the 8 MSB to match the above. What do they sound like?


That depends on whether there was data in the 8 MSBs that you threw away. If there was data in there, than you hear the result of clipping. You have a mess.

If there the signals were typical and there was data that you threw away in either case, then the following is *not* true.

QUOTE
IME 1) = always white noise, 2) = sometimes white noise, but sometimes distorted mess with something vaguely related to the original signal clearly audible.


Looks to me like a gedanken experiment that went kerflooie because it did not treat the most common situation, which is data in the MSBs.
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googlebot
post Mar 3 2011, 14:10
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Besides all the swagger I think Arnold's point, that you get massive clipping of those components belonging to the stripped MSBs, really is a show-stopper issue. A lot of what you hear in the isolated 8 LSBs is just that.

Would transforming to the frequency domain, stripping all components above a certain threshold, and converting back give more meaningful results?

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Arnold B. Kruege...
post Mar 3 2011, 14:58
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QUOTE (2Bdecided @ Mar 3 2011, 05:57) *
QUOTE (Stereoeditor @ Mar 2 2011, 18:26) *
As I said in an earlier posting, I didn't comment in my AES presentation on the audibility of what was happening in bits 17-24, only that while there was often random bit activity, with some recordings there was some signal-correlated activity in the 8 LSBs.
What do you mean? I'm not trying to argue or nitpick - but honestly, what do you mean by this?

I know what "signal-correlated" means, but it's not immediately obvious to me how you make this judgement in this case.



Exactly. The only reliable way I know of to establish a system's perforamance with low-level signals is to resort to contrived signals, including test tones.

Now that fade outs and reverb tails have been excluded by some, its really hard to find clearly identifiable low level signals that everybody is going to like.
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2Bdecided
post Mar 3 2011, 14:59
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Guys guys, this is getting way out of hand. I pursue one little aside of an aside in a thread - for reasons that have nothing to do with the point of the thread, and (as it happens) nothing to do with any potential audible advantages of 24-bit vs 16-bit audio, and Arny repeatedly tries to give me a lecture on dither.

Stop trying to answer questions I haven't asked.

I am looking for real acoustic recordings that are so clean that there's no hope in hell of them self dithering at 16-bits. JA's aside implied that he'd found some (if you think it through). Or else he has found some other way of determining what's above and below the noise floor - which in itself would be worth investigation (because I think that's a very complicated topic).

Either such recordings exist, or else dither is almost pointless (think about it). I don't have many 24-bit recordings, but of the ones I have to hand on my PC, none appear anywhere near that "clean". None appear to need those 24-bits (even ignoring the limitations of the human ear); none appear to even need dither. So I was wondering which recordings JA had found which has something non-random-ish in the 8 LSBs, and how he determined this fact.

That's it. No more. No less.

I'm beginning to wish I'd just PM'd JA! wink.gif

Cheers,
David.
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Arnold B. Kruege...
post Mar 3 2011, 15:42
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QUOTE (2Bdecided @ Mar 3 2011, 08:59) *
I am looking for real acoustic recordings that are so clean that there's no hope in hell of them self dithering at 16-bits.


AFAIK no such thing exists. The current record holder among commercial recordings a tad less than 15 bits.

I know how to make such a recording, but the method would be really not meet the stated criteria.

QUOTE
Either such recordings exist, or else dither is almost pointless (think about it).


Even though such recordings don't seem to exist, there is still plenty of use for dither. Many steps in audio production still need it.

OTOH, let me explain how to make a recording of a real world performance that for sure needs dither. I just make the widest dynamic range recording I know of, but make it with say 10 dB headroom which is merely good practice.

The peak level moves from FS to FS -10 dB, and the quietest passage moves from FS -88 dB to FS - 98 dB. The need for dither is clear. The need to produce the recording with > 16 bit resolution at the live recording session becomes clear.

Expand on that a little and you will see that it is easy to make recordings with music-related information in the 8 LSBs of 24 bits. Just convert a 16 bit recording to 24 bits and attenuate by 8 bits which is about 48 dB.

Other ways to do this exist, but they net out to about the same thing.

If you want to be stuffy about having music in the upper 8 bits, learn how to do dyanmic range expansion with 24 bit precision. ;-)
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Stereoeditor
post Mar 3 2011, 18:34
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QUOTE (krabapple @ Mar 3 2011, 02:27) *
QUOTE (Stereoeditor)
But to the public at large, who have been told that even low-bit-rate satellite radio is "CD quality," the difference between lossless and lossy bit-rate reduction is not as clear as you might expect. To judge by some of the emails I receive, that difference isn't even as clear as I would expect among Stereophile's readership. That was the point I was making.


But to then NOT tell the public at large (or at least, the sample in the room with you, or in your letters column ) that detection of audible difference between lossy and lossless is not necessarily predictable from the difference signal, would be disingenuous at best. So I'm sure you make a point of mentioning that.


Yes I did. (And didn't you already ask me this question?)

John Atkinson
Editor, Stereophile
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Stereoeditor
post Mar 3 2011, 19:01
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QUOTE (2Bdecided @ Mar 3 2011, 05:57) *
QUOTE (Stereoeditor @ Mar 2 2011, 18:26) *
As I said in an earlier posting, I didn't comment in my AES presentation on the audibility of what was happening in bits 17-24, only that while there was often random bit activity, with some recordings there was some signal-correlated activity in the 8 LSBs.
What do you mean? I'm not trying to argue or nitpick - but honestly, what do you mean by this?

I know what "signal-correlated" means, but it's not immediately obvious to me how you make this judgement in this case.


Set the 16 MSBs to 0 and examine what bits 17 to 24 contain in isolation.

Regarding dither, I note you said in another message that you were "looking for real acoustic recordings that are so clean that there's no hope in hell of them self dithering at 16-bits." I looked into this at length several years ago. The problem is that with low-noise mikes and preamps, recordings of acoustic music tend to have have brown or red noise floors, so while the RMS audioband level of the noise is above the 16-bit quantization floor, you can't assume that there will be spectral content at the LSB level to provide optimal dithering. If not, then of course, there is no dithering action. If the noise has the right spectral content but is somewhat too high in level, with an undithered quantizer you get noise modulation of the signal, something that Stanley Lipshitz demonstrated at an AES convention many years ago.

So why not always use dither of the right PDF and level, just in case the signal might not be self-dithering? It can't do any harm and it might be needed.

Having said that, when Keith Howard wrote an article on the subject for Stereophile - http://www.stereophile.com/features/705dither/index.html - he disagreed somewhat: "The message I hope you take away from it is that dither—for all its wondrous ability to confer analog-like behavior on digitized signals—should be applied with care, particularly at the 16-bit level. In converting some 24-bit files to 16-bit it may be unnecessary to use dither, and the sound quality may benefit from its deletion."

Note, BTW, that Keith also found many 24-bit commercial recordings not to have signal-related activity below the 16th bit, which is one of the points I made in my AES presentation.

Thanks for the feedback, David.

John Atkinson
Editor, Stereophile
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Arnold B. Kruege...
post Mar 3 2011, 19:46
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QUOTE (Stereoeditor @ Mar 3 2011, 13:01) *
Set the 16 MSBs to 0 and examine what bits 17 to 24 contain in isolation.


The irony of trying to find very small signals in the face of such massive clipping!

The fallacy of believing that small signals are only contained in the LSBs.

Not exactly reasonble ways to find the Holy Grail.
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Stereoeditor
post Mar 3 2011, 20:18
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QUOTE (Arnold B. Krueger @ Mar 3 2011, 13:46) *
QUOTE (Stereoeditor @ Mar 3 2011, 13:01) *
Set the 16 MSBs to 0 and examine what bits 17 to 24 contain in isolation.


The irony of trying to find very small signals in the face of such massive clipping!


What "clipping"?

QUOTE
The fallacy of believing that small signals are only contained in the LSBs.


What fallacy? It was purely the nature of the contents in bits 17-24 that I was asked to examine.

John Atkinson
Editor, Stereophile


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googlebot
post Mar 3 2011, 20:38
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Cutting LSBs is fine, but cutting MSBs leads to serious distortion due to clipping. It's not trivial to understand why this happens but you'll get to it when you think about Arnold's example of two concurrent waves with different volume and how the louder one also modifies the LSBs. When you cut out the MSBs in that case, you won't be left with only the quieter wave but the latter + clipped artifacts of the louder wave.
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Wombat
post Mar 3 2011, 20:42
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I read the discussion about 24bit with very high interest cause it suddenly pops up everywhere on the net. Most likely cause of Apples decision.
It would be great to have a thread with some of the infos that were already posted in here could be started. If anyone has an idea?
On Slimdevices there are 2 threads for example discussing this subject.
But now that someone answered with a further link to "computeraudiophile" i thought we need a thread here i can link that people to smile.gif

This post has been edited by Wombat: Mar 3 2011, 20:43
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Notat
post Mar 3 2011, 21:18
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QUOTE (googlebot @ Mar 3 2011, 12:38) *
Cutting LSBs is fine, but cutting MSBs leads to serious distortion due to clipping. It's not trivial to understand why this happens but you'll get to it when you think about Arnold's example of two concurrent waves with different volume and how the louder one also modifies the LSBs. When you cut out the MSBs in that case, you won't be left with only the quieter wave but the latter + clipped artifacts of the louder wave.

A few points:
  1. Clipped white noise is still white noise.
  2. If we hear anything that is signal dependent in the LS bits, that's very strong evidence that there's information in those bits - reduced entropy indicates presence of information.
  3. If we only hear noise it does not necessarily eliminate the possibility that there's information there - there are many cases where useful information is white.
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