John Curl's Blowtorch preamplifier part II

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We were talking of mixing desks bus preamps. They work in inverting mode. Each time you plug-in a new track in the mix, the gain of the OPA increase automatically.
I noticed that, when you listen to a single track, if you plugged many other muted tracks, on most of the mixing desks (VFA), its sound turned dull, compared to the same all alone.
According to my wife from the kitchen, CFAs cured the issue, to the great delight of our friend Waly. ;-)

Wow! To know that all these decades we have had to cope with more dull sound the more instrument tracks were recorded! Good that you and your wife clearly heard it! That's clenches it, thanks for the education :xmasman:

Jan
 
In no particular order I have found the following.

Perception, lines per inch...couldn't find the citation.
However, in the authors same body of work he discusses
"Human eyes are exquisitely sensitive to color variations:
a trained colorist can distinguish amount 1,000,000 colors, ...."

Tufte, E. (1990). Envisioning Information. Chapter 5, Color and Information.
Graphics Press. Cheshire, Connecticut. USA

Attended the seminar. What was very interesting is that Tufte passed around the
second book ever published from the Gutenberg Press. With that he commented
that even way back then, the second book contained a pop up that remained affixed
to the page and after some 530 years the quality of that was such that the pop up
still to this day didn't create wrinkles on the page. When the book came round
to me for inspection...I took it and left the seminar, got arrested at the vintage
book sellers convention across town. They confused me with the suspect who
just walked away with a portfolio of sacred and holy illuminations from the Vatican.

The first book off the Gutenberg Press was the Bible. The second book published
was also a very important work...anyone know or care to guess what it was?
Yes, it was a book with pop ups in it too, like the children's books. It has
as many applications today, probably more so, than when it was originally
published by print and published by hand written text.


Thoughts on learning or desiring knowledge.
Are best summed up by the words of Dr. Edwards Deming

"It is unknown and unknowable."
"No one can possibly know."

And, he gave an example of someone going to a seminar about
growing Egyptian cotton and coming up with an entirely new
process for doing something...I forgot specifically what it was.

Deming's point was that nobody knows what a person will take away
from learning something...regardless if it's directly job or work related,
or whether the person will put that knowledge to work immediately or not,
it shouldn't make any difference.

My own observations are similar and I've had more than my share of
people questioning me as to why I want to know or learn something.
This is especially so in education where it is perceived that subjects
are clear and distinct.

For example I was fortunate enough to take some educational units
at the Federal Reserve Bank. When school resumed the following
year, I was able to incorporate real world examples of finance and
economics to my math students and they learned from it.

Sadly, most of my colleagues got stuck with the same old educational
mumbo jumbo. Imagine 20 - 40 years the same educational credits,
teaching how fractions work to 6th graders. You do it once or twice
and know how to do it. And know that if kids can't multiply kids
can't go on. Then it's just a matter of knowing how to think out
of the box and motivating kids for "Drill and Practice".

Thanks for the bandwidth.
 
Yes. Better to clip cleanly at line level, than hit the power amp hard and then complain that the output stage doesn't clip cleanly---IMO.

I agree.
You can have a look on this 1980 patent too
Distortion free power limiting and clipping prevention circuit
George
Behringer B2031 limiter circuit.
The limit signal is derived from output stages peak values.
Behringer limiter.png

Dan.
 
Why are there more than one dithering noise shape?
Which is best one and/or when to use that one vs another?
THx-RNMarsh
From Cool Edit Pro v2.1 help file.
Dither Depth (bits)
This sets the bit amount of Dither to be applied. Generally, values of 0.2 to 0.7 give the best results without adding too much noise. Note, however, that as this value is lowered, other unwanted harmonic distortion noise will appear. (You can usually get away with lower values for the Dither Depth when you use Noise Shaping.)

p.d.f.: The “probability distribution function” controls how the dithered noise is distributed away from the original audio sample value. Five p.d.f. types are available from the drop-down list: Rectangular, Triangular, Gaussian, Shaped Triangular, and Shaped Gaussian.

The Rectangular function means there’s an equal chance that the noise value added will lie anywhere between +1 and -1 (i.e., the likelihood of a value of -0.8 being chosen is the same as that of 0.2, or 0.3, or any value between -1 and +1).

The Triangular function chooses random numbers that are generally closer to 0 than to the edges -1 or +1 (i.e., the chance of 0 being chosen is twice as great as the chance of choosing 0.5 or -0.5). All dithering distribution functions can linearize the quantization noise, meaning that the noise that’s heard doesn’t depend on the frequency of the dithered audio, thus no harmonic distortion appears. The SNR Loss is measured against the undithered case. If modulation is present, the audible noise floor rises and falls depending on the amplitude of the signal, so generally one doesn’t want this either.

p.d.f. SNR Loss Modulation

Rectangular 3dB Yes
Triangular 4.8dB No
Gaussian 6dB Negligible
Shaped Triangular 4.8dB No
Shaped Gaussian 6dB Negligible

The p.d.f. types are arranged from those having highest harmonic distortion, but lowest additional noise (Rectangular) to least harmonic distortion but highest additional noise (Gaussian).

Usually a Triangular p.d.f. function is a wise choice, because it gives the best tradeoff between SNR, distortion, and noise modulation.

Dan.
 
True and that's not bad for us...I'll have to find the exact number,
we can perceive a significantly higher resolution than our computers
screens provide, I want to say something in the order of 11,000 or 17,000
lines per inch.

Thinking the audio perception range is 2 - 4 time our hearing bandwidth.
Stewart Hegeman and others have described the research. I don't think
I've ever read the original or primary research papers only secondary
if someone has a primary source and care to share I would appreciate it.

roughly we resolve lines at 0.3 arc minutes from some stuff on viewing pictures I have read, then there is this:
http://www.swift.ac.uk/about/files/vision.pdf
This is interesting also:
http://www.cambridgeincolour.com/tutorials/cameras-vs-human-eye.htm

I don't think you need figures that high, 4K on a 24 inch monitor is 180 pixels per inch and that looks quite good, I would think a 1000 pixels per inch would be more than enough. Using 11,000 pixels per inch on a 24" wide screen monitor gives us a 31680M pixel display..... rather more than we can resolve I believe.
 
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And this
Clarkvision Photography - Resolution of the Human Eye

As to lines per inch there are many factors such as viewing distance, looking at the circle of confusion may provide more answers, found this:
1.Visual acuity. For most people, the closest comfortable viewing distance, termed the near distance for distinct vision (Ray 2000, 52), is approximately 25 cm. At this distance, a person with good vision can usually distinguish an image resolution of 5 line pairs per millimeter (lp/mm), equivalent to a CoC of 0.2 mm in the final image.

From...
Circle of confusion - Wikipedia, the free encyclopedia

Plenty of stuff out there regarding the circle of confusion and ability to resolve detail, I have been playing about with this for doing large prints at high DPIs of photos and playing with big stitched panoramas 20,000x4000 pixels 5:1, print/screen size and viewing distance is important. I have also read that some of the smart devices retina screens are approaching human visual acuity at 400 dpi...
 
Using a good photo printer at 300 DPI (output from the software) the standard for photos give excellent results and is generally the standard for photo prints, though I do believe the resolution from the printers is actually better as the dots are sort of (dare I say it) dithered.....Mine can do DPI in the thousands, but my basic photos are only 7360 x 4912 pixels, I can print out at 300dpi A2 and still get the same look as a 4"X6" snap...
How Image Resolution Affects Print Quality - Photoshop Tutorial
 
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Wow! To know that all these decades we have had to cope with more dull sound the more instrument tracks were recorded! Good that you and your wife clearly heard it! That's clenches it, thanks for the education
I'm not the only one to had noticed-it. I knew sound engineers who used to chain several bus to minimize this phenomena.
Neither i know a lot of commercial mixing desks witch used CFAs here.
Not to forget that large mixing bus is a very sensitive place for RFI etc. and that, with CFAs, we can use lower impedance for the feedback paths.
So i don't understand your irony, if it is so.
Do-you have, you too, this strange allergy to CFA topology ?
 
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Do-you have, you too, this strange allergy to CFA topology ?

Not at all, I'm pretty agnostic here, have used both. I do not share your religious hang-up on CFAs either.

But I would think that a competent console designer would take care of these things no matter discrete, VFA, CFA, tubes, what have you. It seems pretty straightforward engineering to design for flat freq response even with 30 inserts in any technology. It's not that such things elude the most basic freq response measurements.

Jan
 
https://forums.adobe.com/thread/370714

300 dpi per pixel the 4 colours smudge together to make a pixel of the required colour, though as the above shows offset printing is done by lpi, offset printing the image is printed from the plate to a rubber buffer then to the paper.

Color offset is half-toned with a screen, it was quite an art getting the angles right when making color separations to prevent moire patterns. The dot are still resolvable under magnification. I suppose this has been highly automated these days.

Vector Halftone Week: introduction to vector halftones - Astute Graphics
 
But I would think that a competent console designer would take care of these things no matter discrete, VFA, CFA, tubes, what have you. It seems pretty straightforward engineering to design for flat freq response even with 30 inserts in any technology. It's not that such things elude the most basic freq response measurements.
Sorry, but that are FACTS.
Like cars manufacturers designed all RWD before Citroen 15 Traction...
The thing, i suppose, was because many desks used OPAs, and there were only VFAs at this time.
And, as long the specs were 20-20 000Hz at +-0.5dB, specifications were filled.
Market was more sensitive to the features, noise of the mike preamps, numbers and flexibility of the correctors, automation, quality of the faders, look, reliability etc.
Don't believe that most of the mixing desks (monitors, amplifiers etc.) were top of the audiophile gear. A fashion market.
I do not share your religious hang-up on CFAs either.
My taste for CFAs is everything but religious. I use this topology where and when it brings more advantages than inconveniences comparing to others. Here, an obvious case. Only reason why i talked about here.
 
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Color offset is half-toned with a screen, it was quite an art getting the angles right when making color separations to prevent moire patterns. The dot are still resolvable under magnification. I suppose this has been highly automated these days.

Vector Halftone Week: introduction to vector halftones - Astute Graphics

I didn't even want to go into that, it could be a total pain, that's why they use lines per inch, the image should be 1.5 to 2X PPI the required LPI to create the halftone image.
Nice link, brings back happy memories of my old Art courses.....
 
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Sorry, but that are FACTS.

Ahh, its facts you are after.
OK, see attached.

Your insertion of 30 extra channels means a loss of loop gain of 30 x which happens to be close to 30dB also.
The lowly 20 cents each in quantities CFA NE5532, used in consoles by the millions probably, clearly shows the effect of falling bandwidth with gain, of course.

Actually, going from unity gain to 30 dB noise gain (with 30 inserts) lowers the closed loop bandwidth from 10Mhz to about 250kHz. It's a tribute to your and your wive's ears that you can clearly hear this difference! ;)

Jan
 

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