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Topic: Help me put this guy back in his right place (Read 24504 times) previous topic - next topic
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Help me put this guy back in his right place

Reply #25 –
Quote
this thread is also going to sway the beliefs of the rest of the population in the forum. >_<

You poor misguided fool.

!



As for noise shaping and SDMs, I'll use these pictures for a simple explanation:

http://metrology.hut.fi/courses/s108-180/L.../Luento9/sd.pdf

Look at the first and second order SDM ADCs. Ignore the last box in each - that converts the 1-bit output to multi bit.

The first order is the simplest to understand: Figure 8.20, the SDM is inside the box. Note that the system is clocked, so it can only send things round the loop once per clock cycle.

Let's assume the output can only be -1, or +1. It's really 0 or 1, but changing the range makes the maths easier. Also, let's assume that the comparator has a very slight positive bias - otherwise, in this simple system, with absolutely no noise, we're going to get stuck.

Now, consider silence. That's an input equivalent to zero. The input to the integrator is zero, the 1-bit comparator has to jump one way or the other, it's slightly biassed, so jumps to +1. Output = +1.

Next clock cycle. (B) = +1, Vin=0, the output of the integrator = -1, the output of the comparator =-1. Output = -1.

Next clock cycle. (B) = -1, Vin=0, the output of the integrator = 0, the output of the comparator = +1. Output = +1.

We're back where we started.


So, a first order undithered DSM encodes pure silence as a square wave at half the sampling frequency. That's true. That's why we use higher orders, and a little dither to break the pattern up. But even in this simple example using a simple system, you've got to admit that the noise shaping works: there's none in the audio band - it's all at fs/2, which is 1.4MHz on SACD.


Now, consider your idea. Calculate the output throughout the duration of the signal, and then do the subtraction. The output would be +1 throughout, and then the subctraction would make it -1 throughout. So silence gives a negative digital full scale signal? Hmm - that doesn't work at all!


Any good?

If not, my fees as a private tutor are £50 per hour. ;)


Cheers,
David.

Help me put this guy back in his right place

Reply #26 –
Quote
Quote
this thread is also going to sway the beliefs of the rest of the population in the forum. >_<

You poor misguided fool.

!


LOL  I guess you're right... anyway, I asked a mod to close that thread and it actually got closed with a somewhat positive note for me, so I won't be wasting any more time on this either way... er... congratulate me! CONGRATULATE ME!    (w00t) 



Hmm, I understand some of what you are saying, but then we are back to the basic definition of delta-sigma as 'sum the difference...'. I have people at my university I could ask about this, I suppose that will be faster  Thanks

Help me put this guy back in his right place

Reply #27 –
LOL.
You are to be... congratulated.

But you better be ready if he starts a new thread.

Please don't engage in personal attacks, but be VERY subtle if you want to. By calling him names people will have a lowered impression of you no matter your technical superiority in the issue that was at hand.

Help me put this guy back in his right place

Reply #28 –
I don't know if you should be congratulated - if you used that kind of insulting language (and unattributed quotes!) on HA you'd be warned, then banned. But you probably already know that.

Next time, if I have time, I'll join the discussion if it helps.

Cheers,
David.

Help me put this guy back in his right place

Reply #29 –
Well, there are differing standards on different forums--head-fi.com was a very polite place when I first posted there but apparently it has gotten a lot more rough lately. bbs.stardestroyer.net, the forum I've been frequenting more these days, is a madhouse, where you're just not treating yourself fairly if you don't throw some insults back at all the people that have piled curses and mockery on you, and people have this elaborate theory that insults are just used to emphasize points and do not detract from the quality of your argument if the argument itself is sound. (!) I guess some of that has rubbed off on my posting style. :x

But the people at bbs.stardestroyer.net were driven into their current style of debating by a certain very annoying debater who uses very polite language, whose arguments are all wrong but all take an extraordinary amount of time to pick apart, and jumps from point to point, never addressing the main issue and never admitting defeat. Quite similar to the person I was debating

But enough excuses  I'll be sure to conduct myself properly here.

Help me put this guy back in his right place

Reply #30 –
Quote
Quite similar to the person I was debating

No, he thought it was right, and was doing his best to express it. I think you were unfair on him.


Anyway, you can kill his argument with some facts:


Prerequisites:

The psychoacoustic theory in this field is almost non existent. (So you can't say, for certain, "the signal is different in x, y, or z dimension, hence it will sound better". You can say the signal is measurably better/different, but you can't draw concrete conclusions about what this will sound like).

As a consumer, you will never be in a position to make a fair comparison.


DSD fundamentals:

1-bit coding was proposed because the best DACs at that time were 1-bit DACs. That is no longer true.

1-bit coding is neither optimal, not perfectible. There are inherent non-linearities, which it is impossible to remove. (They can be reduced to a level at which they are probably inconsequential).

1-bit coding adds large amounts of ultrasonic noise. The effect of large amounts of ultrasonic noise upon audio systems is well known, and the effect is audible. Whether it is a good or bad effect is debatable (though it may explain the preference for the "sound" of SACD), but incorporating it within the audio format itself is a dubious decision.

The use of 8-bit "DSD Wide" doesn't remove any of these problems. It just makes it possible to edit the stuff without cascading and multiplying the problems. The fact that DSD wide was created proves that the problems are real, and that they become significant when 1-bit DSD coding is used several times in series. That should ring alarm bells.

The delivery format (SACD) is still 1-bit. There is no magic that says you can avoid all the above 1-bit problems by originating in 8-bit and then converting. (You can reduce the problems, but you don't have these same fundamental problems with DVD-A at all).


DSD Advantage? :

Material mastered on Analogue tape has a limited high frequency response (bandwidth). You can say that the tape deck is experiencing frequencies which are simply so high (so fast) that the equipment cannot respond. You could also call this effect a "filter".

This high frequency response (bandwidth limit) of most analogue master tapes exceeds the limit of CD. It does not exceed that of DVD-A. A "brick wall" (or more gentle) filter, as used at the high frequency limit of PCM systems, will only ring if it experiences spectral content within its transition band. An analogue master tape does not contain any frequency content this high, or any transition this rapid, so the filter in a PCM system is inconsequential.

For such content, the anti-alias filter has no effect in the time or frequency domain (apart from removing any very high frequency equipment noise). There is no signal present, temporal or spectral, that it can possibly impact. Hence, the shorter impulse response of SACD (which is only really shorter under certain conditions and constraints) is immaterial when transferring material from analogue masters.


Consider that last point. Some SACD fans believe SACD sounds better than DVD-A. They claim that this due to the fundamental difference(s) between the formats. The only valid technological "advantage" is the shorter impulse response (less ringing) of SACD vs DVD-A. However, this difference (whether we can hear it, or not) is irrelevant for all those archive recordings released on SACD. (It's also irrelevant for the large number of 24/96 recordings upsampled for SACD  ).

So, if there is an "audible" difference, it's due to mastering, ultrasonic noise, ADC quality, DAC quality, placebo, and/or (just possibly) non-linearity.

In other words, any "audible" difference, if it really exists, has nothing to do with the formats supposed superiority, but due to intentionally introduced (and format irrelevant) differences.

i.e. You can do a good or bad mastering job with either format. You can add ultrasonic noise in any DVD-A player if you want. You can use the same ADCs and DACs for both processes (remember: the best converters are no longer 1-bit devices). We can all imagine things. And if you want more non-linearity, well, use a distortion box!


This still leaves the possibility that a new all-digital “pure” DSD recording might sound better than a DVD-A recording, if the shorter impulse response is an audible advantage. Maybe. Who knows. What is certain is that, for the vast majority of SACD content out there, any superiority over DVD-A content (real, or imagined!) has nothing to do with the format or digital coding parameters.


To be fair to SACD, there are two other issues. Assuming that the ADCs and DACs are good enough assumes that there is a good filter in use when converting DVD-A. For high sampling frequency PCM, the requirements can be similar to SACD, but they're usually more strict. A bad filter may cause a bad sound. This is more of an issue with DVD-A than with SACD. Though it should be possible to do an excellent job quite easily when sampling at 192kHz!!!

Also, if you do need a 192kHz sampling rate, that's too high for multi-channel audio on DVD-A.

Neither of these impacts my "analogue master tape" example, which must be answered before we can take anyone seriously who claims that SACD sounds superior to DVD-A with such material.


A final thought: Both formats should be more than good enough. Surround sound is a much bigger issue.

If the basic sampling on DVD-A and/or SACD isn't good enough (and I can imagine that! After all, we’ll have to be sold something new in another 30 years) then you need a high sample rate multi-bit system which is half way between both formats. Before going down that route (and, tbh, before deciding between SACD and DVD-A) we really need to understand the psychoacoustics and engineering that's at work here. The format war means this is in the interests of neither side, so marketing has taken over from engineering.

Cheers,
David.

EDIT: added "To be fair..." paragraph.

Help me put this guy back in his right place

Reply #31 –
Hi Folks,

Courtesy of Joe Bloggs, I have come to learn of your august forum and some of the posts are rather very enligthning as well as the fact that I noticed that 2Bdecided knows Prof. Hawksford personally, whose paper in the Optical Disc Systems Journal, I refer to as the dissenting paper on head-fi.org.  Some of 2BDecided and KikeG answers are very helpful and I would hope that you folks could probably help me with some questions that I have on DCS Elgar/Elgar Plus/ Mark Levinson No.30.6 linearity plots.  After Joe's unwarranted outburst I went back to check out the original linearity plots of the an earlier Elgar implementation


The updated linearity plot after the implementation of DSD is very different



And now the Mark Levinson 30.6


The key differences to a casual observer (of which I am) is that the Mark Levinson is dancing along y-axis beyond -100 dBFS, and this  becomes more aggressive as it approaches -120dBFS The original Elgar seems to have a cut-off in this region and Elgar Plus has the cleanest plot. What would account for this differences? Previous comments on the Elgar Plus are noted, thanks in advance for your helpful comments.

Help me put this guy back in his right place

Reply #33 –
While I'm not an acoustician or an electrical engineer, there are a number of problems with the paper linked that are not insignificant to this discussion.

  For one thing, the article is not testing whether one particular method of audio data storage is superior to another. All tests use a heavily modified signal capture, master and reproduction system based on the SACD.

  What the paper appears to claim is that certain (which among those used, they dont appear to say) recordings made with a certain recording system, mastered with a certain technique, and played back with a proprietary speaker system may change (how much is unclear) in certain individuals' (they dont say who, how many tested, what background) levels of blood flow and electrical activity in the brain in a statistically significant fashion when a high cut (>22KHz) filter is not on. This apparently correlated to subjective measures of sound quality ("more pleasant") in the same  individuals (who were queried in some unmentionable method of "psychological evaluation", the results of which they dont bother to mention).

  This has rather little relevance to whether SACD is a "better sounding" recording media than DVD-A (24/96 or 24/192) since DVD-A media was not used in any part of the testing here, and hence no comparisons between the same recording played back on DVD-A and SACD systems were made

  In addition, the signal path in every stage of the experiment was manipulated in a non-standard fashion using extremely esoteric and/or proprietary equipment.
 
  In particular, the primary DAC used was a higher frequency unit (3.072MHz) than is used in SACD mastering, largely because a lower noise floor than found at hypersonic frequencies (in traditional SACDs) was desirable. The system also featured esoteric "pre-emphasis" and "de-emphasis controllers" to furthur minimize noise at hypersonic frequencies (or something).

  Most troubling about the system they used was that they did not appear to compare the low-pass signal plus ultra and hypersonic noise versus the full range signal at any point.
 
  They also did not bother to introduce any other high-cut filters outside of the 22kHz one, which is also quite troubling, since AFAIK high-frequency perception does vary to a not-inconsiderable degree. Also, the relationship of the supertweeter to the rest of the speaker setup is questionable -  the supertweeter (mimimum output frequency: 3KHz) is driven directly by the dedicated hypersonic amplifier and turned off completely in the case when the high-cut is employed.
 
  Also, one of the two data sets they do bother to graph appears to show subjects adjusting the volume of the full range signal to be higher than the high-cut signal. The amount of the adjustment done relative to the high-cut appears to be <1dB (max).

    There are a large number of questions about the methodology, and most importantly about the raw data, that are simply not addressed at all in this article.
I would wager the previous article in the Journal of Neurophysiology would have, at least, more data presented.

   
    Strangely enough, the article appears to be intent on selling equipment (and the hypersonic test disc) manufactured by Action Research. 
edit: fixed italics

Help me put this guy back in his right place

Reply #34 –
The Journal of Neurophysiology paper

thanks audible!, are there other credible papers on this topic because most of those that I have come across are from Japanese universities.

thanks in advance

EDIT: added a link

Help me put this guy back in his right place

Reply #35 –
I'm not supporting or refuting anyone's position concerning advantages or disadvantages of SACD vs. DVD-A, but in regards to this article...

Quote
The Journal of Neurophysiology paper

...and concerning psychoacoustic audio compression in a broader capacity, does this tend to refute the concept that lowpass does not change the effect of sound on the listener?  Or has the contention always been that lowpass makes no significant change in the effect of sound on a listener?

Could these results (and similar results in other studies, if they exist) stand as evidence that the use of lowpass in psychoacoustic audio compression is, to some measurable extent, detrimental to sound quality?

Excerpt from article (final paragraph)...
"In conclusion, our findings that showed an increase in alpha-EEG potentials, activation of deep-seated brain structures, a correlation of alpha-EEG and rCBF in the thalamus, and a subjective preference toward FRS, give strong evidence supporting the existence of a previously unrecognized response to high-frequency sound beyond the audible range that might be distinct from more usual auditory phenomena.  Additional support for this hypothesis could come from future noninvasive measurements of biochemical markers in the brain such as monoamines or opioid peptides."

Note: I am not making a statement or "taking a position" here, only asking questions in the pursuit of better knowledge of the subject.

Help me put this guy back in his right place

Reply #36 –
Welcome theaudiohobby!

I can't explain the linearity graphs until I check how the Audio Precision determines these values. I've seen those kind of ripples before somewhere - IIRC it was due to a non-linearity, or possibly incorrect dither, or even no dither at all. That's just an "off the top of my head" guess - I'll try and find out more about what the AP linearity test involves.


IIRC The Hypersonic effect had a time constant of (typically) around 2 minutes, but I'll have to go back and re-read the paper (not this week - far too busy!). I thought we'd discussed it here before, but a search doesn't find it. Still, it's probably in one of those SACD/DVD-A/CD threads in the FAQ. IIRC, despite claims in the paper, there were doubts that high level ultra sonic signals could be reproduced without generating in-band (i.e. audible) distortion components.


ScorLibran, be careful drawing comparisons between the Hypersonic effect (if it exists - IIRC it's the only research group to have shown this, and the experiment hasn't been repeated or confirmed by others) and (selective or static) low pass filtering in psychoacoustic based codecs. 96kHz sampling adds another octave compared to CD quality, 192kHz sampling adds yet another octave. Low pass filtering 44.k1Hz sampled material down to 19kHz removes approximately three semitones.

So, even if this missing inaudible information has an effect, it's desperately tiny compared with the amount added by high resolution formats. What’s more, very few other people are claiming that these extra high frequencies have some effect on human listeners directly. What they do suggest is that the filtering in CD quality audio has some small effect. mp3 and MusePack etc use filtering by the bucket load - if it is a source of audible problems in CD, then it should be 10x more of a problem in psychoacuostic based codecs.


If proven, the Hypersonic effect raises other questions. If the main benefit of including ultrasonic frequencies is to introduce a subconscious change over several minutes, cannot the same effect be caused by simulating this ultra sonic content.


If, as a consumer, you expect to be able to answer any of these questions using information provided by any interested party, or your own testing, then you're sadly mistaken. That is, until someone issues identical material on DVD-A and SACD.

Cheers,
David.

Help me put this guy back in his right place

Reply #37 –
Quote
ScorLibran, be careful drawing comparisons between the Hypersonic effect (if it exists - IIRC it's the only research group to have shown this, and the experiment hasn't been repeated or confirmed by others) and (selective or static) low pass filtering in psychoacoustic based codecs. 96kHz sampling adds another octave compared to CD quality, 192kHz sampling adds yet another octave. Low pass filtering 44.k1Hz sampled material down to 19kHz removes approximately three semitones.

So, even if this missing inaudible information has an effect, it's desperately tiny compared with the amount added by high resolution formats. What’s more, very few other people are claiming that these extra high frequencies have some effect on human listeners directly. What they do suggest is that the filtering in CD quality audio has some small effect. mp3 and MusePack etc use filtering by the bucket load - if it is a source of audible problems in CD, then it should be 10x more of a problem in psychoacuostic based codecs.


If proven, the Hypersonic effect raises other questions. If the main benefit of including ultrasonic frequencies is to introduce a subconscious change over several minutes, cannot the same effect be caused by simulating this ultra sonic content.


If, as a consumer, you expect to be able to answer any of these questions using information provided by any interested party, or your own testing, then you're sadly mistaken. That is, until someone issues identical material on DVD-A and SACD.

Cheers,
David.

Thanks David.  That puts it into perspective.  Here is the section of the FAQ (the "High Definition Digital Audio" portion) I had been studying on the subject, which I had read before as well.  I know the effects of lowpass were thought through and discussed many times by the codec developers, but I wasn't fully clear on the extent of such effects.

Help me put this guy back in his right place

Reply #38 –
I didn't notice the statistical analysis (table 2) in the html version (it is just linked, not displayed).
In fact, this is interesting : 26 listeners, an ABBA double blind test, 10 statistical analysis.
In 4 of them the full range playback was recognized from the lowpassed one (22 kHz, 80db/octave) with a probability that they were guessing <1 %, in one of them the probability was <5 %, and in the 5 other, the probability was >5%.

If 1 % is taken as threshold, the probability of failure in case of guessing is 99 %. Now could someone calculate the probability of getting at least 4 successes (p<1%) in 10 trials ?

Help me put this guy back in his right place

Reply #39 –
I get p<0.0002 % can someone comfirm this ?

Help me put this guy back in his right place

Reply #40 –
prob=0.00000200127615694084 or 1 / 500 000.

(n:=10;
p:=1/100;
sum(binomial(n,k)*p^k*(1-p)^(n-k),k=4..n);)

Help me put this guy back in his right place

Reply #41 –
Thanks. So we can say that in this experiment, the 22 kHz lowpass was perfectly ABXed.

Help me put this guy back in his right place

Reply #42 –
Quote
If, as a consumer, you expect to be able to answer any of these questions using information provided by any interested party, or your own testing, then you're sadly mistaken. That is, until someone issues identical material on DVD-A and SACD.

Cheers,
David.

Agreed and that is the reason that the constant dross that DVDA is technically superior all the more annoying.    This thread has highlighted strengths and weaknesses of both formats and more to  the point it is the commercial success or not of either format that will determine their eventual survival 

Help me put this guy back in his right place

Reply #43 –
Well if there was any 'constant drossing' about the 'superiority' of DVD-A I certainly didn't have anything to do with it 

Re: ABXing the 22kHz cutoff:

Quote
the supertweeter (mimimum output frequency: 3KHz) is driven directly by the dedicated hypersonic amplifier and turned off completely in the case when the high-cut is employed.


Thus it seems that the 'lowpassed' and 'non-lowpassed' versions are not at all identical below 22kHz, in fact they are different starting at 3kHz?

Help me put this guy back in his right place

Reply #44 –
No, because the people couldn't distinguish the super tweeter playing alone at full volume from complete silence.

Help me put this guy back in his right place

Reply #45 –
 at what frequencies

Help me put this guy back in his right place

Reply #46 –
My understanding is that this tweeter has a frequency response starting at 3 kHz, and that it was fed with highpassed signals at 22 and 26 kHz, according to the experiments.

Help me put this guy back in his right place

Reply #47 –
Quote
My understanding is that this tweeter has a frequency response starting at 3 kHz, and that it was fed with highpassed signals at 22 and 26 kHz, according to the experiments.

That's what the diagram in the first article appears to show - the supertweeters were being driven directly by the highpassed amplifiers with no contact with the "audible range" amps.
  The comment about 3KHz was regarding the starting frequency of the driver - Pioneer claims flat response from 3-100KHz for that particular beryllium ribbon driver.

  22KHz is likely going to be audible to some few people, but those people were apparently not involved in the test.

  As I said before, my primary concern with the method involved here was that there was an assumption made that  <22KHz + hypersonic (musical components) is going to be superior to <22KHz + hypersonic (noise).
  This assumption did not appear to be tested in either article.


 
Quote
Agreed and that is the reason that the constant dross that DVDA is technically superior all the more annoying.


  Given that the frequency response of DVD-A can reach 96KHz and the SACD (when heavily tweaked to reduce noise) can go slightly over that, I don't see how either article shows the superiority of one medium over another in any way (especially since they were not compared at all).
    Certainly I don't see any 'dross' (not sure if that works grammatically here) about the superiority of one medium over another here, but I myself would be tempted to suggest the DVD-A is probably slightly superior for reasons of equipment price if not SNR.
    High Quality 24/96 recording is readily availible to just about anyone who has a few hundred dollars in their pocket, and resolutions that high IMHO, are significant overkill to begin with. The overhead protects you from drunken mastering engineers, maybe.
   
  The problem is, both SACD and DVD-A mediums are so high resolution to begin with that the mastering process is very likely going to be the limitation on the sound quality from any particular recording.

Help me put this guy back in his right place

Reply #48 –
Quote
The problem is, both SACD and DVD-A mediums are so high resolution to begin with that the mastering process is very likely going to be the limitation on the sound quality from any particular recording.

So far nothing new under the sun 
In theory, there is no difference between theory and practice. In practice there is.

Help me put this guy back in his right place

Reply #49 –
Phew, gee, I was wondering what happened to this thread and the whole General forum