Author Topic: New feature: Ask Dr. Stupidus!  (Read 28347 times)

Gen. Dreedle

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Re: New feature: Ask Dr. Stupidus!
« Reply #75 on: February 13, 2014, 01:30:31 AM »
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The active probe (usually) have 50Ω output impedance and if it is (usually it is) designed for special types of scopes, the scope it is switched automatically to 50Ω input impedance.

Uh...........no, not exactly. Well, maybe some of the fancy new Tek ones do............the ones that don't use an external supply, but.............

Us old farts use active probes that need an external supply. Mine has a switch, that the operator has to move, to either use the 50R termination, on the scope, or use its internal 50R termination, so you can use it with a regular ol' 'scope.

Hate to nitpick, but they brought it on themselves.

(Mine is so old that you can no longer read the lettering for INT/EXT 50 ohm termination. What can you expect from uPay, for around $50. Including supply. So, don't let them tell you I am full of crap.)
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seagreen

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Re: New feature: Ask Dr. Stupidus!
« Reply #76 on: February 13, 2014, 01:41:31 AM »
What?  Don't you know that you need a DFB laser with mono-mode glass fiber for that 2 meter optical link?  Jeeeezzz....

All to avoid a common mode connection!
No double blind testing was used in the making of this post.

MystereoN

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Re: New feature: Ask Dr. Stupidus!
« Reply #77 on: February 13, 2014, 11:16:45 AM »
But if inquiring mind want to know, Toslink cables are usually made from borosilicate glass (glass) or polymethyl methacrylate (plastic).
Refractive index for borosilicate glass (depends on material used) is between 1.51x and 1.52x, Abbe = 58 to 66.
Refractive index for polymethyl methacrylate is 1.49x, Abbe = 58.
Other materials as polycarbonate are much worse, with refractive index of 1.59, Abbe = 31
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seagreen

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Re: New feature: Ask Dr. Stupidus!
« Reply #78 on: February 13, 2014, 02:42:40 PM »
But, none of this matters:

"Jitter is easy to measure and compare. Audibility of jitter is another matter - most tests show that jitter has to be pretty severe to be audible. In any case, jitter is mostly caused by noise, and not by the transmission characteristics of the cable."
No double blind testing was used in the making of this post.

Gen. Dreedle

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Re: New feature: Ask Dr. Stupidus!
« Reply #79 on: February 13, 2014, 06:25:05 PM »
More wisdom, from the guy who doesn't understand the virtual ground thing......................(I know, 'cuz I had to 'splain it to him, and gave him permission to post our private conversation...........and saw the reaction of the rest of the over-educated idiots)..............

Quote
Yes, it's the digital value, the stream of one's and zero's that determines the sound. Not the voltage amplitude, not the shape.

I am not going to waste my time trying to re-educate him. He is on his own.

Maybe he should stick to the audio side of audio.
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"Danby. D-A-N-B-Y."
"Take him out and shoot him."
"Sir?"
"I said take him out and shoot him. Can't you hear?"

Gen. Dreedle

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Re: New feature: Ask Dr. Stupidus!
« Reply #80 on: February 13, 2014, 06:27:15 PM »
What?  Don't you know that you need a DFB laser with mono-mode glass fiber for that 2 meter optical link?  Jeeeezzz....

All to avoid a common mode connection!

So most of the light can bounce back to the source.............

Well, doesn't matter much, with a cheap LED. But just try telling that to a laser.
"Major Danby, sir."
"Danby. D-A-N-B-Y."
"Take him out and shoot him."
"Sir?"
"I said take him out and shoot him. Can't you hear?"

seagreen

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Re: New feature: Ask Dr. Stupidus!
« Reply #81 on: February 13, 2014, 11:42:07 PM »
But, wait!  There's more!

An optical fiber is a waveguide.  Except, it doesn't have hard, ahh, field boundaries like those hunks of copper found at microwave sites.  If they haven't been stolen.

So... How many meters does light have to travel down a mono-mode fiber before it acts like a single mode waveguide?

And, that's not the half of it.

Anyway, this can be made to work if you really want to, but just what would the point be??  For baseband transmission at SPDIF frequencies, it can be easily shown that LEDs, with their spectral composition, have far better low frequency noise performance over fiber than any laser system that is practical.
No double blind testing was used in the making of this post.

MystereoN

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Re: New feature: Ask Dr. Stupidus!
« Reply #82 on: February 14, 2014, 01:49:08 PM »
Q:
Quote
I read somewhere that terminating a short cable with a 75ohm resistor was not necessary, do you think it could help then?
A:
Quote
Not strictly necessary but won't harm either. Suggest having a look on the scope to see what effect it makes. It is unlikely to have an audible effect.

Yes, why bother with termination? Anyway, all sounds the same, it is pure digital, all what matters are 1 and 0  :-\

Dr. Stupidus, should I sell scope + other hardware and invest money into simulation software?
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Gen. Dreedle

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Re: New feature: Ask Dr. Stupidus!
« Reply #83 on: February 14, 2014, 02:56:18 PM »
Dr. Stupidus knows you can't fix stupid.
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"Danby. D-A-N-B-Y."
"Take him out and shoot him."
"Sir?"
"I said take him out and shoot him. Can't you hear?"

Gen. Dreedle

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Re: New feature: Ask Dr. Stupidus!
« Reply #84 on: February 16, 2014, 10:08:18 PM »
Right, and yet so wrong, at the same time:

Quote
I think your point is a good one, but I wouldn't disparage theoreticians like Hawksford. Or bright people like Jocko focused tightly on the things they know extremely well, but aren't terribly important to the system as a whole. We learn a lot from them; once targets are determined, they give us the criteria we need to engineer to meet those targets.

But indeed, the practical guys with experimental results on audibility are the ones who set the targets, and there's not much (if any) audible differences as long as jitter at the DAC is held to less than a nanosecond or so, depending on its spectrum. Listening tests may not be your gold standard, but please understand that many people feel that the goal is an audibly transparent system, not scope pictures that are judged by eye. For those folks, once jitter is below the point where there's audible changes in the analog output, then it becomes a non-worry.

1.) He assumes what I focus on is "not terribly important to the system as a whole". WTF do you  think I do?
2.) He assumes the only guys who do listening tests are the guys he agrees with. HTF does he think what I  think is verified?
3.) The same ol' "nanoseconds of jitter" excuse. I am sick of hearing this friggin' excuse.

If you do not specify the frequency of the signal that you are referring to as having "x nSec of jitter", it is a meaningless number. 1 nSec at 1 kHz is nothing like 1 nSec at 44 kHz and nowhere near what 1 nSec at 11.2896 MHz is.

But, the meter readers.................the guys who tell me I don't know what I am talking about................don't even know how to read the meters they are using.

Stick to polymer science. We do not doubt your knowledge or abilities. Leave the jitter stuff to folks who really know it. You don't. Sorry, but them's the facts, ma'am.
"Major Danby, sir."
"Danby. D-A-N-B-Y."
"Take him out and shoot him."
"Sir?"
"I said take him out and shoot him. Can't you hear?"

seagreen

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Re: New feature: Ask Dr. Stupidus!
« Reply #85 on: February 17, 2014, 11:15:20 AM »
Do you think that most, ahh, "experts" on the subject actually understand what effects are caused by an impure conversion clock in a mixed signal application?

Anyone?  Anyone?
No double blind testing was used in the making of this post.

Gen. Dreedle

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Re: New feature: Ask Dr. Stupidus!
« Reply #86 on: February 17, 2014, 01:48:41 PM »
You can't confuse them with stuff they can't comprehend.

Their attitude is just their rest of their ideas about audio: "Well, it is inaudible, so it isn't important."

They think it is inaudible, so they assume it isn't important. That, and their neurosurgeon mentality convinces them that since audio is much simpler than, say neurosurgery, that isn't hard to know all there is to know. Since there can't be much to know, since it is just audio. Never mind the same principles apply, they just can't be important!

Does that answer your question?

But, back to the issue....................

They are so short-sighted, as they all regurgitate the same excuse about jitter audibility. Never mind that number has its roots in a fixed tone, iow, deterministic jitter. They forget all about non-deterministic jitter. That line of thinking leaves them to believe that jitter only exists if you can see spurious signals, down in the noise level, along with the signal they are measuring the jitter of.

Never mind that signal they are looking at has noise skirts, just like any other signal. That concept evades them. Mainly because the meters they use, to tell them there is x nSec of jitter does not measure that noise skirt.

Which is the type of jitter they need to worry about. That is the jitter caused by the clock.

(Not to say all the crap added by the crappy SPDIF process can be ignored..............it can't! It is really bad, and that is how all this stuff got started. But, once they considered that problem "solved", that meant everything was great.)

Now, one of the overriding arguments has been (and it has a lot of truth to it) is that if a DAC is that sensitive to jitter, it must be a crappy DAC. OK, let's say it is. But how do you get rid of that problem, once and for all?

Easy......................put the clock at the DAC, and ship it over to the transport. (Never mind it no longer operates as a stand-alone DAC, but let's gloss over that, for now.)

OK..........clock at DAC (where it belongs), and no SPDIF-induced jitter, so problem solved.

Right?

Wrong!

In their world, it is. Because they can not see how things really work. (Focusing in on one thing, and ignoring how the entire system works. IOW, doing what they say I do.) But, as usual, they are wrong again.

If the jitter problem is solved, then clocks should not sound different. I know, with 100% certainty, clocks do sound different. The problem isn't solved.

But, we don't do listening tests, remember?

Oh, we do, but we don't have logs of our double-blind tests. So, it can't be valid.

Blow it out yer @$$.

Instead of telling me it doesn't exist, or it can't make a difference, maybe they should try out. (Never mind they can not fully characterize clocks................not my problem!) No, easier to babble on, showing how smart you think you are. When all along you don't have a clue.

And do us a favor....................stop telling us about Howard Johnson. We know who he is....................we have his books. Some of us have actually gone to his classes. So shut up. You are boring, as well as wrong.
"Major Danby, sir."
"Danby. D-A-N-B-Y."
"Take him out and shoot him."
"Sir?"
"I said take him out and shoot him. Can't you hear?"

seagreen

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Re: New feature: Ask Dr. Stupidus!
« Reply #87 on: February 17, 2014, 04:04:48 PM »
Boring and wrong might be the new orange.
No double blind testing was used in the making of this post.

MystereoN

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Re: New feature: Ask Dr. Stupidus!
« Reply #88 on: February 18, 2014, 08:41:16 AM »
Hihi, look to this from bright side: we figured out who we wouldn't trust to design our RF, ADC and DAC printed circuit boards  ;D

Quote
They refer to Howard Johnson, but they really don't get it. Using him to bolster a narrow-minded, pig-headed, and wrong stance, is a disgrace to a really sharp guy

Really a disgrace, since mr. Johnson is advocating signal integrity, not smashed waveforms and "it doesn't matter" ignorant position. Maybe those experts @ DIYA forgot to read his articles, some of them have very nice pictures inside



Or as someone pointed out, simulatoritis is spreading around  ;D
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seagreen

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Re: New feature: Ask Dr. Stupidus!
« Reply #89 on: February 18, 2014, 02:48:47 PM »
I think that they don't even bother with simulation.  Why?

As somebody has said, these are solved problems.  Solved for decades.

No double blind testing was used in the making of this post.