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Old 9th May 2013, 01:23 AM   #751
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It's remarks like this...

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Originally Posted by abraxalito View Post
...his moment of clarity lasts only the one sentence.
...that lead to this...

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Originally Posted by abraxalito View Post
...nobody's particularly interested
...because fair-minded people recognize that your argument is, in all probability, driven more by envy than substance.

Present something that it's easier to disagree with on a point-by-point basis without the inclusion of prejucicial asides and perhaps you'll generate a bit more interest.
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Old 9th May 2013, 08:45 AM   #752
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Originally Posted by Ian Finch View Post
I've seen this argument a few times and whilst I have no beef with it, I can't help wondering why Doug's designs are singled out when there must be literally thousands engaged in professional audio design, all making similar mistakes, if that's what they are.
I have yet to notice DIYA threads about the designs of those thousands of engineers. But should I notice one in the future I'll make a note to explain the mistake to them too.

In fact its only a mistake in a technical sense, not an economic one. To be successful in the professional audio design business you just need to deliver customers what they want at the right price, and this business doesn't sell on IMD performance as there are no standardized, relevant IMD measures. The two do that do exist (CCIF, SMPTE) aren't relevant since the stimulus signals are not music-like.

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If this design flaw is one that admits significant levels of IMD whilst virtually squishing THD, it must be obvious enough for other designers to largely avoid, so it surely is surprising that the matter isn't raised more commonly and in reference to specific designs such as discussed here.
Other designers do designs which largely avoid IMD and which post relatively unimpressive THD figures. If you've not seen them here on DIYA then may I suggest getting out a bit more? Thorsten Loesch is one designer who's been quite active here in the past in this area. Pedja Rogic comes to mind as another who's posted up schematics of zero feedback I/V stages for DACs. Probably Nelson Pass is another?

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Perhaps a few relevant IMD facts and figures would help this along constructively.
What kind of facts and figures do you have in mind? You could do worse than turn up some old papers on the topic - R/A.Belcher has one such paper (WW, 1978) which has been linked to here on DIYA recently, he cites a much older paper by Brockbank and Wass.
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Old 9th May 2013, 08:56 AM   #753
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Originally Posted by counter culture View Post
...because fair-minded people recognize that your argument is, in all probability, driven more by envy than substance.
Surely fair-minded people wouldn't fail to recognise lack of supporting evidence and reasoning for this assertion would they?

As something of an afterthought, if someone makes an unreasonable argument, it remains unreasonable whether it was motivated by envy or purest compassion. So how is what 'drives' my words at all relevant?
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Old 9th May 2013, 03:14 PM   #754
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Originally Posted by abraxalito View Post
R/A.Belcher has one such paper (WW, 1978) which has been linked to here on DIYA recently, he cites a much older paper by Brockbank and Wass.
Yes, even I have linked to Belcher's paper here fairly recently. However, my understanding is that DSP systems have supplanted his method. I would be interested to know more about their use.

That might be the source of facts and figures of interest for your suggestion of looking at musical stimuli for the measurement of IMD, I imagine.
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Old 9th May 2013, 05:47 PM   #755
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the Multitone/complex IMD/Noise Power Ratio/Noise Fill Test simply don't reveal anything new or different about basically decent analog electronics - despite the guru driven propaganda

http://twain.unl.edu/school/audio_old/doc/14381.pdf

look at the pictures (I did) - the various multitone/noncoherence test measures are below or very comparable to the THD, 2 tone IMD when normalized

multitone IMD total power decreases for increased number of tones - if you naively reduce each by 1/n to keep worst case crest factor within the same peak amplitude

the various schemes for packing/selecting low crest factor multitones striving to maintain high RMS level doesn't result in "music like" signal - musical signals are highly harmonically correlated, have large crest factors and overall 3-5 kHz "power bandwidth"


there are no design techniques for lower IMD with moderate or high THD


I have shown intentional design can give pathological high IMD - requires multiple extreme frequency shaped paths and multiplier stages


when called out Nelson had to admit his “tsunami of IMD” article was exaggerated for effect – a shame to see a solid technologist pandering to a audience


care to show us an “interesting result” of any of these non-conventional measurements – that isn't also evidenced by THD vs Level, Frequency sweeps, 2-tone IMD? - not that I would just look at the summed distortion power when fft is so cheap and easy today

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Old 10th May 2013, 12:52 AM   #756
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'Interesting run-down and comments, thanks jcx. My money is on the simple realisation that very low distortion audio is not what audiophiles hoped it would be.
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Old 25th June 2013, 08:10 AM   #757
owdeo is offline owdeo  Australia
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Anybody interested in building Mr Self's latest preamp (with tone controls) that is features in the latest Linear Audio magazine?

A low-noise preamplifier with variable-frequency tone controls
I've just received my copy and was very interested to see what he'd done. The input stage is now balanced and similar to the Elektor 2012 design, and the output stage is pretty much the same Baxandall active gain stage but parallelled once. The tone control section is almost the same with some minor changes to values to accommodate 5k pots to achieve lower noise. LM4562 opamps are now specified throughout instead of 5532s.

The variable tone controls in my '96 Precision Preamp work beautifully so I'm sure they would in the new design would too. I'm not convinced by the active gain stage though - I'm still not happy with the sound and I feel that this is the most likely culprit, though I don't really have any rational explanation as to why. Pity, I really wanted to this preamp to be the heart of my system and expected it to sound transparent, but it doesn't. The problem is definitely not that the distortion is too low, as some have suggested. I have it set up so I can flick between it and another preamp and between the source (which is the output of another preamp so I can control volume, having carefully matched the output levels of the other preamps to unity gain). The '96 preamp seems to add a sort of artificial edge to the sound, and the soundstage depth is reduced. It is a slight effect and probably wouldn't bother some. To me it is an interesting lesson on what happens when you design for measurements and regard checking with your ears as unreliable and pointless.

If you believe that good measurements of THD and noise are the only requirement for a good preamp and audiophiles are all kidding themselves all the time, then build it - it will work beautifully and you will love the tone controls if you're into that sort of thing. But if you like to use your ears and find that different amps offer different "flavours" to your music, even though it might be hard to pick them in a full double-blind test, I'd suggested looking elsewhere. I find this statement troubling, as I very much admire Mr Self's anti-BS stance and while many have suggested possible reasons for the sound quality impairment, I'm not confident of being able to find a measurement that would show why and prove it, and this to me is a very unsatisfactory position to be in. Nevertheless I'm not about to disbelieve my ears.
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Old 25th June 2013, 02:58 PM   #758
Struth is offline Struth  Canada
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Hi Guys

Rod Elliot has an interesting article about IM on his site.

I haven't looked at this thread for quite a while and have not read the whole thing, so the following might already have been stated: It has been known for many decades that IM is much more bothersome to the listener than THD. IM has to be at least an order of magnitude lower than THD to be considered "nonproblematic", although this is likely not low enough.

Where THD has at least some semblance of musical relation, IM products are distinctly nonmusical. It takes a lot of brain power to filter out the noise this represents, and listener fatigue is the result.

In general, the methods used to reduce THD and noise also reduce IM.

There is also a general impression when first hearing really transparent equipment that the sound is "boring", or even "lifeless". There is often a lack of bass, or midrange "fullness", due to the lack of emphasis and distortion of those frequencies and thus the absence of their distortion harmonics. You have to train your ear to recognise "transparent" or "good" sound for what it is. This may cause an internal conflict, because we are nostalgaic in our sound exploration, always searching for the original experience of enjoying what we are hearing as we did long ago.

That said, I am not nostalgaic about certain amps I've built over the years. One example is the JLH, which I built in many forms to many different power levels. Playing it louder just made more mud and detracted from musical enjoyment. I believe the only way one can enjoy such a circuit - or any of the recent Pass twiddlings - is to listen to very simple music. Indeed, those who design and build such circuits always evaluate it with simple music. Try playing dense pop or classical through those circuits and the 'good impression' will quickly disappear.

With regard to Doug's preamp design, I think the issue is likely one of IM and/or of a THD profile build-up through so many opamps that might be a bit on the "edgey" side of subjective view. Such an edge can be perceived as "crispness" or "detail" in low quantities, as with odd-order THD. However, if that edge has significant IM content then it will always be objectionable.

Doug mentions IM very infrequently if at all throughout his texts. One would assume he has made such measurements as no doubt the Precision Preamp and updated forms are likely the basis for commercial products, as well as just for articles.

Have fun
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Old 25th June 2013, 03:56 PM   #759
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Oh, you're kidding... There are better chips than these out there. What ever
+1

According to Self, all cables sound alike too.
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Old 25th June 2013, 05:17 PM   #760
redjr is offline redjr  United States
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...Indeed, those who design and build such circuits always evaluate it with simple music. Try playing dense pop or classical through those circuits and the 'good impression' will quickly disappear....
Great points Kevin. Not sure what you are referring to as 'simple music', but my test is to use a wide range of acoustic instruments, well recorded and mixed. Forget about testing an amp using the typical pop music of today and all the associated electronic instruments involved. Electronic instruments seem to add their own layer of distortion. An awful lot of it sounds terrible - IMO. I'll take an acoustic guitar, piano, stringed, brass, woodwind instruments and drums to really test - not only an amp, but speakers as well. Remember... it's all about trying to faithfully reproduce the illusion of the original recording. That's the best we can hope for.

Rick
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