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Old 12th August 2013, 02:35 AM   #1641
fas42 is offline fas42  Australia
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Certainly agree about the total system distortion ...!! Every step adds its own litte bit - I suspect having too many different types, characters of distortion is more important than the total amount, as far as one's hearing goes. Trying to sort out all the different distortion signatures, unconsciously, while listening becomes stressful - multiplies the fatiguing factor ...

With regard to the 8K frequency, just recently did a little experiment, for other reasons, of digitally chopping off all frequencies above a certain point, on a dense pop mix with lots of treble content. This was on simple PC speakers, which still can produce an audible 18kHz tone.

Using only casual listening, it was obvious that a lot was lost if the cutoff was 8kHz; 10kHz it became more subtle, but by 12kHz it was all but undistinguishable from the original. Only with very, very careful listening, which I didn't try, would I have been able to pick the variation ...
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Old 12th August 2013, 03:10 AM   #1642
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I am referring to 8KHz in music content. but, you are right about the 12Khz point. In fact, the BBC did similar studies and came to same conclusion -- their BBC monitor need not go beyond 12kHz.

Now there are plenty of others who have done studies from a different angle and determined higher freqs were important and lent a different character to the sound.

So for a high-end design you might need to use the best/worse case numbers and try for them..... they wont always be needed but this is for the Highest of Hi End performance. Take no prisoner level. Use the widest range and the lowest number to be sure everyone, under any condition -- even a fluke combination of errors will not be audible. Very Low, very high, very wide, etc. Perfection.

It really, truely has to be looked at as a system including all the interfacing, emi/rfi issues.

Hey! If it was easy we would have music that sounds like real music being played in our listening room a long time ago... instead of nice hi-fi sound.

Thx-RNMarsh

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Old 12th August 2013, 03:43 AM   #1643
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Quote:
Originally Posted by fas42 View Post
To try and get to the heart of the matter I looked up some material from Analog Devices, who might just know a thing or two about such things, . Jung's "Op Amp Applications Handbook"
I was looking at the very same outstandingly useful body of work myself - available in bite-sized chunks here : ADI - Analog Dialogue | Op Amp Applications Handbook

Since the discussion has polarized into CFA vs VFA part6 of the above also introduces applications of the AFA which subjectively I find gives excellent results despite being more akin to VFB than CFB.
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Old 12th August 2013, 03:48 AM   #1644
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Part of the problem, as I see it, is that the sound often gets subjectively worse as you approach peak quality - it's only because I've been there many times that I know that I have to 'punch' through that psychological barrier, keep persisting in applying all the tweaks until the SQ breaks through into the 'clean' space - this is particularly so with digital replay .

Others may have tried various procedures, and to their ears the quality was getting worse: more aggressive, shrill, overdone. So they back off, go the "nicer" way - which is pleasant enough, but will rarely lead to the improvements which is real progress ...
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Old 12th August 2013, 03:49 AM   #1645
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Quote:
Originally Posted by fas42 View Post
Using only casual listening, it was obvious that a lot was lost if the cutoff was 8kHz; 10kHz it became more subtle, but by 12kHz it was all but undistinguishable from the original. Only with very, very careful listening, which I didn't try, would I have been able to pick the variation ...
12k+ "undistinguishable " ??

I tried this (with an open mind - and a pc ).
David Gilmour - 320Kbs CBR mp3's .... the test source.

At 8k/10K = hi-fi ....ha ha

At 12k = I could tell , easily .. sounded like a lower quality 128-192kbs mp3 , a shallow sound field.

At 15K , I created a low pass preset so I could switch in/out all (most) 15-20k info ..
(below). I could see your point there , but at high volumes with a 100W amp
the 15K+ info was still readily noticeable , the placement of especially cymbals/bells/brushes. The 320K bitrate's improvement DOES exist.
I never tried this , but could always see the lack of 15k+ info in 192kbs material.

I really had to "crank it up" to hear the 15-20k content. No clicks or gaps , I even automated it so I didn't have to move at all. It's there and it counts !


OS
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Old 12th August 2013, 04:09 AM   #1646
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Hmmm, looks like your filter is not truly "brickwall", so knee frequency slope and phase shifts could play a part here. I was using an 8191 tap, the maximum, filter in Audacity which means the cutoff is like a, well, brickwall: 0 to -120dB in close enough to a vertical line drop off ...
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Old 12th August 2013, 04:14 AM   #1647
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The nice thing about a group hug is that it can also be like a rugby scrum: A quick uppercut and no one can prove who did it.

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Old 12th August 2013, 05:43 AM   #1648
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The nice thing about a group hug is that it can also be like a rugby scrum: A quick uppercut and no one can prove who did it.

I still feel my VAS dangling from my chin, thanks Bonsai
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Old 12th August 2013, 06:43 AM   #1649
Bonsai is offline Bonsai  Taiwan
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LOL.
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Old 12th August 2013, 09:16 AM   #1650
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Quote:
Originally Posted by fas42 View Post
To try and get to the heart of the matter I looked up some material from Analog Devices, who might just know a thing or two about such things, . Jung's "Op Amp Applications Handbook" directly compares and contrasts the two topologies and states:

Quote:
The CFB topology is primarily used where the ultimate in high speed and low distortion is required. The fundamental concept is based on the fact that in bipolar transistor circuits currents can be switched faster than voltages, all other things being equal.
Seems pretty straighforward to me ...
Not really. The last sentence is factually incorrect. So-called "CFAs" slew faster than classic VFAs because their input stages operate in class-AB. Not that this is not necessarily the case with all so-called "CFAs".

Otherwise, all so-called "CFAs" operate just like VFAs, with the exception of the fact that in so-called "CFAs" the feedback network affects the forward path of the amplifier. Thus the assertion that so-called "CFAs" are founded "...on the fact that in bipolar transistor circuits currents can be switched faster than voltages..." is arrant rubbish.
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