Today I Learned

[gleem]

I just toured the Paul Reed Smith Guitar factory here in Maryland. They recently started manufacturing their own amplifier line. Guess what they use,
vacuum tubes, preferred by more electric guitar players.

 

[phinds]

I just toured the Paul Reed Smith Guitar factory here in Maryland. They recently started manufacturing their own amplifier line. Guess what they use,
vacuum tubes, preferred by more electric guitar players.

And Macintosh is still using tubes for amps and preamps. I have read, but can't give you a citation, that while it is true that tubes were much better in high end hi-fi systems than were early transistors, that is actually no longer the case, even though you can still find lots of hi-fi enthusiasts who swear by tubes over transistors.

 

[jim hardy]

In one fairly scientific study i read they analyzed signals from tube and solid state amplifiers with fft spectrum analyzers and found no difference when using recorded material.

Puzzled by musicians' preference for tubes in absence of measurable difference, they handed a microphone to a rock musician who, to the surprise of the engineers, immediately turned the gain full up and screamed right into the microphone severely overdriving the preamplifier.
Not surprisingly they found solid state amplifiers with symmetric +/- power supply clip positive and negative peaks symmetrically, so the positive and negative peaks when viewed on an oscilloscope are mirror images of one another. That's symmetric distortion.
Tubes however enter cutoff and saturation quite asymmetrically so positive and negative peaks look a lot different from one another, and that's asymmetric distortion..

Fourier of signals with symmetric distortion of peaks has odd harmonics, asymmetric distortion has even harmonics.
The ear picks up on those different harmonics, which i think musicians call "overtones".
So the two amplifier types sound different when abused.

That was the best study i encountered, it was around 1984.

 

[Astronuc]

All US Hostages in Pakistan Could Have Been Saved, Green Beret Says
http://news.yahoo.com/us-hostages-pakistan-could-saved-green-beret-says-152013771--abc-news-topstories.html

 

[mfb]

Electronics should be able to mimic this saturation effect, if the consumers like it.

 

[jim hardy]

Electronics should be able to mimic this saturation effect, if the consumers like it.

They're working on it... Professional journal IEEE Spectrum got interested
http://spectrum.ieee.org/consumer-electronics/audiovideo/the-cool-sound-of-tubes

Solid-state designers have long attempted to produce tube simulators, using solid-state analog circuits like diode clippers and compressors to produce transfer functions and distortion akin to those of tubed guitar amps. Although these products have attracted only a limited following to date, the recent appearance of solid-state amplifiers based on digital signal processing (DSP) and using physical modeling algorithms, has stirred some interest among serious musicians.

And from http://www.theaudioarchive.com/TAA_Resources_Tubes_versus_Solid_State.htm

Further reading explains in detail the effects that harmonics have on sound coloration:

" The primary color characteristic of an instrument is determined by the strength of the first few harmonics. … The odd harmonics (third and fifth) produce a "stopped" or "covered" sound. The even harmonics (second, fourth, and sixth) produce "choral" or "singing" sounds. The second and third harmonics are the most important from the viewpoint of the electronic distortion graphs in the previous section. Musically the second is an octave above the fundamental and is almost inaudible; yet it adds body to the sound, making it fuller. The third is termed quint or musical twelfth. It produces a sound many musicians refer to as "blanketed." Instead of making the tone fuller, a strong third actually gives the sound a metallic quality that gets annoying in character as its amplitude increases. A strong second with a strong third tends to open the "covered" effect. Adding the fourth and fifth to this changes the sound to an "open horn" like character. "

Now i'll digress on a personal theory , which pushes PF boundaries, but i'll show that it has some basis..

there's one effect I've never seen addressed in the hi-fi journals, probably i noticed it because of my fascination with electric motors.
A speaker is basically a motor. That it moves means it has dynamic response to voltage or current applied to it.
The signal applied to a speaker should be a faithful replica of the voltage applied to the amplifier input...
But should that replica be a voltage replica or a current replica ?
Because the speaker is a motor with inductance, resistance, inertia, as well as counter-emf from its motor action,
its impedance is complex meaning current through it and voltage across it will have different waveshapes - remember your derivative function.

Now - solid state amplifiers employ voltage feedback to make output a voltage that replicates input.
Tube amplifiers of the 1960's employ way less feedback, my Motorola SK47 console had around 10%.
Does a tube amplifier replicate its input with output voltage or with output current?

A pentode tube has high impedance, observe the flatness of pentode's current vs plate voltage curve...
from http://www.6moons.com/industryfeatures/zen8/zen8.html

The pentode tube output stage will do its best to deliver a current that replicates input voltage.
If one is testing the amplifier with an 8 ohm resistor load, of course the voltage developed will have same shape as current for V=IR and R is not complex. Tube and transistor amplifiers will look the same.

Replace the simple 8 ohm resistor load with a complex electric motor(speaker) and it's a different story.
Now V = IZ and Z includes jX_l and f(velocity), so the voltage and current waveshapes are no longer identical .

Exaggerating just a little, one might accuse a tube amp of being an ideal current source and a solid state amp an ideal voltage source.
Current sets the force applied to the cone, while voltage sets counter-emf hence velocity of the cone.
A speaker driven by a current waveform will not have the same motion as one driven by an identically shaped voltage waveform.
So the two amplifiers will produce different sound through the same speaker .
Whether the ear can detect the difference i cannot say. I was taught that the ear is insensitive to phase,
so only amplitude not phase of individual harmonics in the Fourier series would be noticed.One wonders whether this effect had anything to do with recent(to me anyway) standard for speakers to have resistance 80% of nominal impedance, to assure damping with low-Z_out transistor amplifiers?? Indeed better books on speaker design say to include amplifier output impedance, which is low for a voltage source and high for a current source.

Anyhow that's a personal theory and i apologize if it puts anybody off.. But here's the basis i promised at the beginning:
In an old PF thread i mentioned i'd once encountered a Dynaco solid state amp belonging to a local "Guitar-Zan" youth that employed feedback as all solid state amps do. But this one's feedback was measured from output current by a sampling resistor not from output voltage at the speaker terminal. Guitar-Zan described it as "Warm sounding".

Now three decades later i run across this regarding feedback in another Dynaco model, ST120:
http://www.updatemydynaco.com/documents/OriginalAmpModuleAnalysis.pdf

Page 5 of 5
© Daniel M. Joffe, 2011
It’s interesting to note that the feedback is actually current mode feedback, rather than voltage mode feedback. This is owing to the use of
the single transistor, Q1, rather than a differential pair.

I'd assumed Dynaco's current feedback was done to protect output transistors from shorted speaker wires
but maybe they had an ulterior motive ?

It'd be almost trivial to make a current sourcing amplifier
But i'd hear it as an engineer not a musician.

Anyhow -
today i learned I'm not the only one who's noticed current feedback in those Dynaco amplifiers that musical types so love.

And it's being noticed in engineering circles too.
http://www.edn.com/design/consumer/...periority-of-current-drive-over-voltage-drive

Loudspeaker operation: The superiority of current drive over voltage drive
Esa Merilainen -October 22, 2013

This is an overview of the destructive effects that voltage drive has on the performance of electrodynamic loudspeakers. A more comprehensive treatment of the subject can be found in the book Current-Driving of Loudspeakers: Eliminating Major Distortion and Interference Effects by the Physically Correct Operation Method by Esa Meriläinen.

Today, practically all available audio amplifier and loudspeaker equipment works on the voltage drive principle without significant exceptions. This means that the power amplifier acts as a voltage source exhibiting low output impedance and thus strives to force the voltage across the load terminals to follow the applied signal without any regard to what the current through the load will be.

However, both technical aspects and listening experiences equally indicate that voltage drive is a poor choice if sound quality is to be given any worth. The fundamental reason is that the vague electromotive forces (EMF) that are generated by both the motion of the voice coil and its inductance seriously impair the critical voltage-to-current conversion, which in the voltage drive principle is left as the job of the loudspeaker.

maybe suitable for a thread in PFlounge ?

Ohhhh the curse of curiosity...

old jim

 

[nsaspook]

They're working on it... Professional journal IEEE Spectrum got interested
http://spectrum.ieee.org/consumer-electronics/audiovideo/the-cool-sound-of-tubesAnd from http://www.theaudioarchive.com/TAA_Resources_Tubes_versus_Solid_State.htm

Today I learned 'perfection' doesn't sound good to a musician.

 

[2milehi]

There is a right way to tie your shoe laces.

 

[OCR]

There is a right way to tie your shoe laces.

Lots of ways to lace them, too...

http://www.fieggen.com/shoelace/lacing.htm

 

[Astronuc]

How to torpedo one's career - Nobel Prize-winning scientist says he was forced to resign
http://news.yahoo.com/nobel-prize-winning-scientist-says-forced-resign-125443022.html

 

[Astronuc]

Teenagers are losing confidence in the American dream
http://finance.yahoo.com/news/teenagers-losing-confidence-american-dream-114800183.html

http://www.theatlantic.com/business...sing-confidence-in-the-american-dream/395780/How can we change that?

 

[Pythagorean]

Teenagers are losing confidence in the American dream
http://finance.yahoo.com/news/teenagers-losing-confidence-american-dream-114800183.html

http://www.theatlantic.com/business...sing-confidence-in-the-american-dream/395780/How can we change that?

By changing what the American Dream is and not lying to them anymore. It's kind of led to this:

"...in America [...] the poor see themselves not as an exploited proletariat but as temporarily embarrassed millionaires." -John Steinbeck

 

[Stephanus]

Today I learned that speed is relative.
Driving car 20 miles an hour is slow. But try driving backward 20mph...

 

[jim hardy]

But try driving backward 20mph...

What was steering negative feedback (caster) becomes positive !

 

[Stephanus]

Never trust computer with anything important!
I couldn't agree more! I'm a computer programmer myself.
The computer can make mistakes very big and very fast.

 

[mfb]

There is a right way to tie your shoe laces.

Yes, but the video does not show it.
See here

 

[jim hardy]

The computer can make mistakes very big and very fast.

With no remorse at all.

 

[Ibix]

With no remorse at all.

The computer is your friend.

Trust the computer.

 

[Astronuc]

It is estimated that about 4% of persons on death row are innocent. Is that acceptable?

http://www.upworthy.com/30-years-on...oure-freed-the-prosecutor-comes-to-apologize/

 

[mfb]

How many guilty persons get free? And how would those two rates change with suggested action X? I don't know, but that would have to be investigated.
There is only way to reduce this rate to 0 % - don't send anyone to prison. That is not a working model.

 

[jim hardy]

Does the old adage "Better a hundred guilty men go free than one innocent be convicted" suggest 1% is acceptable ?

 

[Astronuc]

How many guilty persons get free? And how would those two rates change with suggested action X? I don't know, but that would have to be investigated.
There is only way to reduce this rate to 0 % - don't send anyone to prison. That is not a working model.

I was reflecting on comments like"
". . . evidence regarding his whereabouts and the murder weapon (which would have swayed them to acquit) were suppressed, according to Ford's attorneys."

and from the prosecutor:

And I knew this was a very burdensome requirement that had never been met in the jurisprudence of which I was aware. I also participated in placing before the jury dubious testimony from a forensic pathologist that the shooter had to be left handed, even though there was no eye witness to the murder. And yes, Glenn Ford was left handed.

All too late, I learned that the testimony was pure junk science at its evil worst.

In 1984, I was 33 years old. I was arrogant, judgmental, narcissistic, and very full of myself. I was not as interested in justice as I was in winning. To borrow a phrase from Al Pacino in the movie 'And Justice for All,' 'Winning became everything.'

Such an injustice.

I certainly don't advocate the guilty go free, but rather, when the system be much more careful and just with regard to depriving someone of their life and liberty.

 

[mfb]

Does the old adage "Better a hundred guilty men go free than one innocent be convicted" suggest 1% is acceptable ?

It's a bit more complicated. For a fixed amount of effort put into the investigation, it is possible (in theory) to derive an ROC curve for court decisions. Different threshold for "this is enough evidence" give different rates of "guilty => correctly identified as guilty" and "innocent => falsely identified as guilty".
The actual ratio of innocent to guilty in prison also depends on the ratio in court. If the police does a "perfect" job and no innocent ever gets accused, then court can go for 100% correct positive rate and put everyone in prison. If most of those are innocent, however, most of them have to get free - which means most of the guilty persons will get free as well.

 

[WWGD]

Prof. Dan Simon argues , effectively I think, that much could be improved in the us justice system, that there is even little effort made to provide a fair trial:

http://www.c-span.org/video/?325568-8/dan-simon-doubt

 

[zoobyshoe]

Sorry for the necropost, but I just read this and the answer came to me while cooking lunch.

Not that hard to show this is not possible: first, check this does not hold for 24!. Then notice that if n>24, then n>10. This is obvious, but notice that multiplying by anything larger than or equal to 10, the factorial will gain at least one digit in length. So , Let N(k!) be the number of digits in k! . We are trying to see when/if we can have N(k!)=k.

Then, given 23! has 23 digits , i.e., N(23!)=23, and N(24!)>24 , we see that N(k!) will increase at least by 1 from k to (k+1), while the digits increase just by 1 , i.e., when we go from N(24!) to N(25!) , k goes from 24 to 25, i.e., increases precisely by 1, while k, the number of digits, increases at least by 1, so there is no way N(k!) can catch up with k , since N(24!)> 24, and the expression in the left will increase at least as fast as the expression in the right. I leave it to you to see what happens when we use a number base different from decimal.

So you have two expressions A,B ; A>B for n>24, and then A goes on to increase faster than B after 24, so B cannot catch up with A.

Go back to post #464 and read forward a few pages.

 

[WWGD]

Ah, OK, let me just delete my post, you can delete yours too, of course. EDIT: just deleted, it; I need to go, but if you delete yours, I will delete mine too.

 

[Astronuc]

The Man Behind 'The Most Interesting Man' Is Interesting, Too
http://www.npr.org/2015/06/20/415835643/the-man-behind-the-most-interesting-man-is-interesting-too

Stay thirsty my friends

 

[Lisa!]

Recently I realized that switiching to a vegan diet might not be as hard as it sounds!

 

[WWGD]

Recently I realized that switiching to a vegan diet might not be as hard as it sounds!

But it will likely be as un-tasty as it sounds, unless you are a gourmet chef and/or can cook Indian-style dishes. I tried vegetarianism, but it was too hard to feel full after eating and I ended up grazing all day long as a result. Besides, if you eat out, options seem limited to eating salads, maybe falafel.

 

[Silicon Waffle]

People can make things that look exactly like hot dogs or sea foods from tofu.

 

[WWGD]

_look

People can make things that look exactly like hot dogs or sea foods from tofu.

_ look like_ is the operating expression. Show me _taste like_ and that can be found when you eat out. I tried all sorts of vegetarian dishes and very few measured up. Specially those vege-sausages. Yikes.

 

[Silicon Waffle]

Yes I agree it is not real ones . People may just be curious only not really interested or fall for them.
The point of vegetarianism I think isn't about being full but being enough. If you are still young and energetic, don't be a vegetarian. I also think it is about food orientation, and it's not stupid at all for a vegetarian to only love vegies instead of meat. I just can't hang loose a piece of meat in front of him in the hope that he will come and swallow it.
I lost my camera and still can't get it back from the cops.

 

[Astronuc]

But it will likely be as un-tasty as it sounds, unless you are a gourmet chef and/or can cook Indian-style dishes. I tried vegetarianism, but it was too hard to feel full after eating and I ended up grazing all day long as a result. Besides, if you eat out, options seem limited to eating salads, maybe falafel.

Yet "Scientists at Beyond Meat concocted a plant-protein-based performance burger that delivers the juicy flavor and texture of the real thing with none of the dietary and environmental downsides." Apparently the have the right ingredients and right process to produce a plant based set of proteins that tastes like beef.
http://www.outsideonline.com/1928211/top-secret-food-will-change-way-you-eat

It is claimed, apparently by the manufacturer, that the plant-based protein has: “More protein than beef. More omegas than salmon. More calcium than milk. More antioxidants than blueberries. Plus muscle-recovery aids. It’s the ultimate performance burger.”

For those who wish to try it - http://beyondmeat.com/products/view/the-beast-burger

 

[Ibix]

...and fewer ethical issues. Not sure about the environmental impact, but it seems plausible that it could be better on that front too.

I'd like to eat an artificial burger one day, just because to be able to do so is such an awesome thing.

 

[WWGD]

The creepy thing is that , when I clicked on "Store Locator" it recommended a store nearby , giving the precise distance, so the page does track down your location. Still, thanks, I will check it out.