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Old 9th October 2012, 08:44 AM   #5131
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Barrows, thanks for sharing your observations. Especially for reporting them in such a reflective manner, which sadly is too seldom seen.

Your personal observations are of course particular to your taste, ears, and system, though nevertheless valid for that particular event. When you support your perspective with that of other highly acclaimed amplifier constructors, you do nevertheless provide your claim with some kind of "general" -quality.

But for that maneuver to be valid these amplifier constructors has to have pointed out exactly the point you make here about truncated upper harmonics. Otherwise you "just" agree on the ncore not being entirely up to the best you have heard. -Which on the other hand isnīt so bad for a plug nīplay DIY amp kit sold for much less.

Personally I can relate to your observation on the sound of the ncore to have some kind of quality to it. That is that the ncore does do something to the signal besides adding gain.
I havenīt had enough time with ncore to add anything to your statement other than I have noticed this in various degrees on all class D amps. That is not to say that class D is inferior to other classes but itīs a quality that seems to stick with them.

As a reason for this "sound" of class D hereunder the ncoreīs that you speak of, the bandwidth limitation might have some validity when looking how it affects the structure of upper harmonics. I found this read interesting on that very subject:

The Sound of the Machine

On the other hand I have a lot of experience with a class A/B construction also with a fair share of nfb inherent to its operation but with a bandwith of > 600kHz and some 3,5 kHz for small signals.

That amp has some of the truncatedness too, but it seems to depend on itīs bias setting. With this amp I can either have truncation of highs or blooming lows. I prefer the best class D to that, as I find this amp unbearable to listen to for either reason...

I am not knowledgable enough to make any statement on what the reasons are for various flavors that these different amps introduce, but my guess would be that the operation of the nfb circuitry is having as much to say on these amps as their ultimate bandwidth.
How does the nfb operation condition the upper harmonics?

If I understand the ncore right, it is the nfb operation that is its major attribute compared to the ucd.
My humble guess is that the algorithm integrated to the nfb on the ncore is both responsible for its major leap forward in SQ to UCD recreating a much bigger and finely rendered image, but also responsible for its "sound".
To what extend can the ncore operation hereunder its algorithm simulate and control upper harmonics?
Could this be a more to the point answer that includes role of the control loop frequency extension?

best,
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Old 9th October 2012, 09:09 AM   #5132
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The new 'ncd' NFB loop seems to have some cunning tricks to increase the open-loop gain, together with real-time fast-acting circuitry to modify the O/L transfer function under the conditions that could normally cause the amplifier self-oscillation to go unstable as a result of the higher O/L gain. (Such as driving the amplifier to clipping with an open-circuit load, which can make the normal ucd circuit switch to a self-osc frequency around 40kHz, as a result of the sharp phase shift transition of the output filter into a High-Z load). I have not used an example of an NCD amp, but worries about upper harmonics seem to be misplaced as the published intermodulation distortion of a a 19kHz/20kHz signal pair look very impressive for a class-D amp.
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Old 9th October 2012, 09:27 AM   #5133
ChrisPa is offline ChrisPa  United Kingdom
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IIRC Bruno said he spent some considerable time comparing (listening to) the amplifier input signal to the output signal

It would be an interesting exercise for everyone to also try that with their amplifier of choice. Hopefully that should help understand which amplifiers add to or take away from the original signal and in what way
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Old 9th October 2012, 09:31 AM   #5134
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Quote:
Originally Posted by Ouroboros View Post
19kHz/20kHz signal pair look very impressive for a class-D amp.
Exactly. As you say, for a class D.

Another question is how this speaks for the composition of higher order harmonics.

A different factor that could have some technical validity in terms of explaining the top end performance of ncore is its high D/F // Low O/P impedance. This represents a major leap forward in terms amplifier-speaker control and may endure such different damping properties to the top end than what "we" are used to experience from electronics. If this has some credentials then the characteristics of the control loop (again) responsible for achieving this high DF will probably show even more compared to previous loops offering lower DF.
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Old 9th October 2012, 10:04 AM   #5135
Ianmac is offline Ianmac  Scotland
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I would be interested in hearing where/how people get source material that has any contents at frequencies above 100 kHz...
The fundamental frequencies of source material is oft described as 20-20Khz.
There will always be a extension to this bandwidth due to the presence of harmonics, these in turn being dependant on the precise shape of the fundamental frequency.
A 10 Khz square wave will consist of a fundamental sine wave at 10Khz and sinusiodal harmonics at 20, 30 40 50 60 70 Khz + etc. These harmonics will decrease in amplitude as they rise in frequency.
In simple terms, this describes the constituent part of a 10Khz square wave and to reconstitute it faithfully the fundamental and all the harmonics must be reproduced in the correct amplitude and phase.
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Old 9th October 2012, 10:13 AM   #5136
Julf is offline Julf  Europe
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Originally Posted by Ianmac View Post
A 10 Khz square wave will consist of a fundamental sine wave at 10Khz and sinusiodal harmonics at 20, 30 40 50 60 70 Khz + etc. These harmonics will decrease in amplitude as they rise in frequency.
In simple terms, this describes the constituent part of a 10Khz square wave and to reconstitute it faithfully the fundamental and all the harmonics must be reproduced in the correct amplitude and phase.
I am familiar with the Fourier series. My point is that there is no need to be able to reproduce a 10 kHz square wave, as your source material (music) won't contain any 10 kHz square waves - the material is already, by the time it gets to the amp, low-pass filtered.

If your source is a CD, there is absolutely no original material over 22 kHz. If your source is vinyl, you might get up to 30 kHz the first couple of times you play the record. Even "hi-res" digital recordings won't contain material above 100 kHz...

"If it's not there, it is not there" is true for harmonics, too...
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Old 9th October 2012, 11:59 AM   #5137
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Originally Posted by Julf View Post
I am familiar with the Fourier series. My point is that there is no need to be able to reproduce a 10 kHz square wave, as your source material (music) won't contain any 10 kHz square waves - the material is already, by the time it gets to the amp, low-pass filtered.

If your source is a CD, there is absolutely no original material over 22 kHz. If your source is vinyl, you might get up to 30 kHz the first couple of times you play the record. Even "hi-res" digital recordings won't contain material above 100 kHz...

"If it's not there, it is not there" is true for harmonics, too...
The very reason for the 18+19kHz intermodulation plot is that higher order harmonics are understood to modulate the audible signal. One thing is whether or not something is there, another thing is whether or not itīs modulational artifacts can be reproduced faithfully...
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Old 9th October 2012, 03:00 PM   #5138
Goto is offline Goto  United Kingdom
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Without wishing to cause a riot, I have to observe that talk of very high frequency (Ultrasonic) components of a sound somehow influencing a waveform after filtering is simply not thought through. All audio we hear (digital, analogue or live) is low-pass filtered, during the recording and mastering process or simply by the human ear.

That process not does selectively leave high frequency artifacts alone to modulate the carrier. There are no higher order harmonics in cd sound, above the 22k limit. None.

Last edited by Goto; 9th October 2012 at 03:04 PM.
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Old 9th October 2012, 03:27 PM   #5139
Julf is offline Julf  Europe
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Originally Posted by Goto View Post
There are no higher order harmonics in cd sound, above the 22k limit. None.
Exactly.

Quote:
Originally Posted by Juhleren View Post
One thing is whether or not something is there, another thing is whether or not itīs modulational artifacts can be reproduced faithfully...
Well, if something is not there, it's modulational artifacts (sic) probably aren't there either, so whether they can be reproduced faithfully or not is a bit of a moot point...
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Old 9th October 2012, 05:21 PM   #5140
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Originally Posted by Ianmac View Post
My understanding (thanks to Fourier when at college)was that the odd harmonics were essential to the faithfull reproduction of a square wave. While we do not have theoretical square waves in our audio signal one can argue that we have a close similarity with rising wavefronts.
Sound is created by physical objects' motion.

It has been correctly observed that no signals contain the leading edge of a perfect square wave.

Even if they did, it would not matter.

Sound id produced by objects moving air, and no object can move with infinite acceleration/velocity, so there are no acoustic square waves to be reproduced.
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Last edited by noah katz; 9th October 2012 at 05:26 PM.
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