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A proposed optical digital cable test - Page 2

post #16 of 138
I didn't mean it as an empirical proof, but I'm sure that you are well aware that your FFT's will all be perfectly identical in the end...and that you'll feel sooooo good telling ppl that they have tin ears if they think that toslink cables matter.
ppl will be impressed for sure...still, I'd suggest a bit more serious measurements if I may
post #17 of 138
joke aside, you could try adding these in the toslink path, w/ a super cheapo coax cable in-between(possibly 2 coat hangers? ):

Amazon.com: Digital Fiber Optical (Toslink) to Digital Coaxial (S/PDIF) Converter: Electronics

Digital Audio (S/PDIF) Coaxial to Toslink Optical Digital Converter

maybe Steve N. could help to measure the J....

PS: another interesting link: Minidisc Frequently Asked Questions
Quote:
In practice, the poor quality optical fibre components often used can tend to introduce data-dependent jitter in the process of separating clock from data in the Manchester decoder at the receiver. This can cause a measureable degredation of the conversion back to analogue format
post #18 of 138
With all due respect (there's lots- your posts are great)- I wonder if a test of digital cables is a good investment of your time. All but the most confused audiophiles (and every engineer and computer scientist) agree that digital signals don't degrade and reproduce perfectly. Mostly I mention this because it would be interesting to me if you could perfect your test of analog cables, as that is where where believers can wage a more honest debate. That is also where a good experiment can truly settle the issue. I looked for your thread on the analog cable test and couldn't find it. Do you remember the title or link so that I may see if that test was/could be more conclusive?
post #19 of 138
Thread Starter 
Quote:
Originally Posted by eucariote View Post
With all due respect (there's lots- your posts are great)- I wonder if a test of digital cables is a good investment of your time. All but the most confused audiophiles (and every engineer and computer scientist) agree that digital signals don't degrade and reproduce perfectly. Mostly I mention this because it would be interesting to me if you could perfect your test of analog cables, as that is where where believers can wage a more honest debate. That is also where a good experiment can truly settle the issue. I looked for your thread on the analog cable test and couldn't find it. Do you remember the title or link so that I may see if that test was/could be more conclusive?
Here you go...

http://www.head-fi.org/forums/f21/my...rprise-405217/
post #20 of 138
Sounds interesting. I have an HT Omega Claro Halo card with optical in & out and an AK5385BVF ADC for the line-in lying around that I could send you, if you think it might be useful in the testing.
post #21 of 138
Quote:
Originally Posted by eucariote View Post
With all due respect (there's lots- your posts are great)- I wonder if a test of digital cables is a good investment of your time. All but the most confused audiophiles (and every engineer and computer scientist) agree that digital signals don't degrade and reproduce perfectly.
This is true except for the fact that SPDIF/Toslink aren't just "digital signals" in the normally understood sense. They carry digital data, but they also carry a clock. The data will get there without error, but the clock signal also has error in terms of phase noise. The claim is that low levels of phase noise, although it doesn't affect data transfer, is audible. I have no opinion on this yet, but depending on the design of the DAC (and ear-brain), it might be plausible.

BTW Nick_charles, if it'd be useful, I'd be happy to lend you my Juli@ soundcard with SPDIF and Optical input. I think it measures quite a bit better than the Edirol.
post #22 of 138
it's well explained how toslink works here, and how a low quality cable can hose things up: About S/PDIF

now how do you measure the differences? stereophile have the right equipment I think.
post #23 of 138
Quote:
Originally Posted by Guidostrunk View Post
The anti-cable trolls will be arriving shortly to tell you it's all a waste of time, and tell you regardless of your findings you will hear no differences.Good luck.
Unlike the credulous believers, fanatics and paid shills, I welcome testing and will accept the results, whatever they may be. Shame that can't be said for those whose income depends on cables or those who blindly accept marketing claims as true.

If test results show a positive difference, I'll buy cables that make an improvement. I fully support Nick's tests, as should anyone else.
post #24 of 138
sadly for the cable haters, you can measure jitter in a digital interconnect w/ the proper equipment: Stereophile: A Transport of Delight: CD Transport Jitter

this sucks, I know...I dearly hope that the OP will find a way to come up w/ this kind of figures.
post #25 of 138
When I'm bored at night, I purposely create jitter.

YouTube - Optical Toslink Fun

Yea, I hover my toslink at my DAC like teasing a kid with candy, makes it crackle.. Lol
post #26 of 138
Quote:
Originally Posted by mmd8x28 View Post
When I'm bored at night, I purposely create jitter.

YouTube - Optical Toslink Fun

Yea, I hover my toslink at my DAC like teasing a kid with candy, makes it crackle.. Lol
You should have whispered then you could have been e-famous like Patrick.
post #27 of 138
What? don't understand.
post #28 of 138
Quote:
Originally Posted by nick_charles View Post
A while back I did a series of crude tests on Analog audio cables. I am considering a set of tests on Toslink optical cables and am petitioning opinions on my protocol.

Equipment
----------

Western Digital HDTV optical output or
Marantz CC4300 CD player optical output

Edirol UA-1EX USB card with optical (Mini-Toslink) digital in

Toslink cables
-------------
  • Freebies and current cheapies
  • Monoprice basic
  • Monoprice premium
  • Two $50 - $60 Toslink cables (I'll buy these)
Toslink to Mini-Toslink adaptor

Lenovo Y710 Ideapad 4GB RAM, Windows Vista 32 bit

Audacity 1.2.4 recording software

Source files
-----------
CD or WAV files

Method
-------
With each cable : same process.

Record a 1 minute segment from the same track/tracks as a digital recording at 16/44.1 at digital max recording level, record a 2nd sample of the same 1 minute , trim and align so that sample 1 and sample 2 are the same length and time-aligned, repeat for samples 3 thru 10.

Analyze the frequency response for all 10 samples 1024 or 2048 FFT. Import the data into Excel, average the results.

Plot the differences between each cables data points.

Choose a sample from each set with the *least* deviation from the mean, uses these as DBT samples, post here for members to DBT.

Suggestions ?
nick_charles,

Since you asked for suggestions, here is my opinion on the proposed test.
I noticed that there some flaws in your test protocol that will undoubtedly reveal no difference whatsoever between the tested cables.

First, you are assuming that your test equipment will let you reveal any difference between those optical cables if such difference existed.
You make the assumption that jitter is not audible below 1 ns, so you don’t use all the ultra-low jitter nonsense equipment used by many “audiophools”.
However, if you want to scientifically prove that there is no difference between optical cables, you would have to use test equipment beyond reproach (even if it doesn’t make sense to you).
In my opinion, a sound card such as the “Edirol UA-1EX USB” (as well as the other two devices you mentioned) is not low jitter enough to show a significant difference between digital cables.
To make a significant test, you would have to use something like the Audio Precision System 2 used by Stereophile or at the very least some professional sound cards that are known to have stable clocks (Lynx Aurora or Prism).
Stereophile has already measured years ago the difference between digital cables.

Second, analyzing the frequency response won’t prove or disprove anything in my opinion. It will be much more interesting if you could measure other parameters that can have a big effect on the sound.
Since we don’t listen at the bits on the digital cable but at the analog output of the DAC (where the jitter shows up). Here is what I suggest.
a)Choose a clean measuring non-upsampling DAC;
b)Select a few budget optical cables as well as reference class glass optical cables;
c)Measure the analog output DAC from a low jitter source (Audio Precision 2, DCS, Lynx Aurora, Prism ...) using a short reference class coaxial cable (such as the Stereovox XV2);
d) Measure the analog output of that DAC with the optical cables.

And for the tests, it would be nice to not only measure the frequency response but also impulse responses, IMD, jitter...

If you do the following test and find nothing significantly different then I will believe that all the Optical cables should sound the same (be it a $1 plastic cable or $1000 super high end glass cable).

However, since I know you pretty well, you are probably going to pretext that even if such a measurable difference existed it would be below the audible range of human hearing and you are probably going to link to a few research papers (it is what you have done countless of time).

The sad thing it that those research papers were not conducted in a proper environment to make such definitive claims. Gladly, there are some scientists that are starting to apply a real scientific and investigative method to this audibility threshold problem. If you read the links below, you will see that when listening tests are conducted with the proper equipment, the human sensitivity to temporal resolution is far greater than previous scientists have assumed before.
Information for prospective students
http://www.physics.sc.edu/kunchur/pa...rge-Foster.pdf

I understand that it is sometimes necessary to make assumptions in a scientific research, however when you start making too much assumptions there is a risk in getting skewed results.

So of course, if the only difference between two cables is 0.1 db in the frequency domain, it would be inaudible to humans. However, by measuring only the frequency response, you are not measuring the temporal response and you are making the assumption that it doesn’t matter.

It is really saddening that people who call themselves objectivists seem to be in fact the most subjectivists of all. They live by a certain set of defined parameters and they don’t try to question themselves. Throughout history scientists has been wrong on many subjects and newer theories have replaced older ones. I just hope that one day more “objectivists” will try to be more open minded and will try to understand why so many people find differences between cables instead of just repeating the same things over and over. In my personal opinion, “objectivists” are the one who are living in a placebo world because they try to believe what some very limited set of measurements tell them despite what their sense tell them.
post #29 of 138
Quote:
Originally Posted by nick_charles View Post
A while back I did a series of crude tests on Analog audio cables. I am considering a set of tests on Toslink optical cables and am petitioning opinions on my protocol.


Suggestions ?
How about splitting the light signal and testing two identical lengths of different toslink cables simultaneously.

Compare the two signals real time in the digital domain, or convert back to analogue with two identical high frequency capable DACs, (on the same clock?).

Matching separately recorded signals at the level of very small time intervals could be a real issue. Perhaps recording simultaneously like this could remove some of these issues.

Good luck and keep us posted how you go.
post #30 of 138
Thread Starter 
Quote:
Originally Posted by slim.a View Post
nick_charles,
First, you are assuming that your test equipment will let you reveal any difference between those optical cables if such difference existed.
Yes, but I can also examine the quality of the transfer by comparing against the original wav signal so that any deviations between the baseline and a recording of a cable under test can be shown. If there was a big difference then the set-up would clearly not be good enough.

Quote:
You make the assumption that jitter is not audible below 1 ns, so you don’t use all the ultra-low jitter nonsense equipment used by many “audiophools”. However, if you want to scientifically prove that there is no difference between optical cables, you would have to use test equipment beyond reproach (even if it doesn’t make sense to you).
I have not mentioned jitter at all in this thread, until now.

Quote:
In my opinion, a sound card such as the “Edirol UA-1EX USB” (as well as the other two devices you mentioned) is not low jitter enough to show a significant difference between digital cables.
The Edirol merely acts as a pass-through taking a digital signal and passing it through as a USB stream. Unless you happen to know the jitter measurements for the Edirol you are speculating. Likewise my other components you do not know the jitter measurements.


Quote:
Second, analyzing the frequency response won’t prove or disprove anything in my opinion. It will be much more interesting if you could measure other parameters that can have a big effect on the sound.
Any deviation in the frequency response between cables will show that there is a difference between cables, jitter shows up in sidebands or in random noise, both will affect the FR as will other added distortions.

I have a very good measuring Entech 203.2, but this involves an extra D/A and then A/D set of steps which means that any variability in the A/D step could mask differences. I do not have the kit to measure other parameters.

Quote:
However, since I know you pretty well, you are probably going to pretext that even if such a measurable difference existed it would be below the audible range of human hearing and you are probably going to link to a few research papers (it is what you have done countless of time).
If you read my first post again I was going to make samples from each cable available for others to test thru listening not assume that differences were inaudible, do not put words in my mouth.

Quote:
The sad thing it that those research papers were not conducted in a proper environment to make such definitive claims. Gladly, there are some scientists that are starting to apply a real scientific and investigative method to this audibility threshold problem. If you read the links below, you will see that when listening tests are conducted with the proper equipment, the human sensitivity to temporal resolution is far greater than previous scientists have assumed before.
I will read those papers and get back to you...
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