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A proposed optical digital cable test

post #1 of 138
Thread Starter 
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
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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
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  • 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
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CD or WAV files

Method
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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 ?
post #2 of 138
Do you think you could directly connect the optical output to optical input with connectors without the actual cable? Also what length glass optical cable do you want to use? I recently ordered something from yourcablehookup.com and they have really discounted glass optical cable, will see if they can cancel my order and let me add a glass cable for you.
post #3 of 138
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.
post #4 of 138
Thread Starter 
Quote:
Originally Posted by haloxt View Post
Do you think you could directly connect the optical output to optical input with connectors without the actual cable? Also what length glass optical cable do you want to use? I recently ordered something from yourcablehookup.com and they have really discounted glass optical cable, will see if they can cancel my order and let me add a glass cable for you.
A direct connection is not possible. I was thinking about using 1M cables. I will check out the yourcablehookup.com site, thanks. I do have a budget for this, but want feedback before I sepnd cash. I have been through this loop before and want to address concerns in advance.
post #5 of 138
Thread Starter 
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.
I am skeptical myself which is why I would rather create samples for others to test and mostly confine myself to the magnitude of measurable differences, I will do my own blind tests of course but cannot avoid my own biases.

My aim here is to see what is wrong with my method before expending the effort...
post #6 of 138
Quote:
Originally Posted by nick_charles View Post
I am skeptical myself which is why I would rather create samples for others to test and mostly confine myself to the magnitude of measurable differences, I will do my own blind tests of course but cannot avoid my own biases.

My aim here is to see what is wrong with my method before expending the effort...
I'll keep a eye on this just to see what your findings are, seems interesting.
post #7 of 138
The Sony POC-DSE10 Digital Audio Optical Toslink Cable is quite impressive!

I'm trying to convince myself that I'm not an anti-cable troll...but trying to hear the refined improvements with my non-audiophile level of hearing, is like splitting the atom. Or the one that's in my brain when it comes to making distinctions between different cables

On a price issue - the Sony costs around £40; a digital plastic Toslink freebie thrown in with some other gear costs ...well, free. No contest.

So how did I end up with the expensive Sony one then?
post #8 of 138
The only thing I'd suggest for protocol is use a foot massage machine on top of cables to try to measure vibration induced differences as some claim to have vibration protection. Wonder if it might make a difference to convert it to analog and then analyzing, like the author of xxhighend claims will show the effects of media player jitter.
post #9 of 138
Thread Starter 
Quote:
Originally Posted by haloxt View Post
The only thing I'd suggest for protocol is use a foot massage machine on top of cables to try to measure vibration induced differences as some claim to have vibration protection.
I could jiggle them about a bit !

Quote:
Wonder if it might make a difference to convert it to analog and then analyzing, like the author of xxhighend claims will show the effects of media player jitter.
That would introduce an intemediary step and while a digital to digital *should* be clean the D/A/D model adds a step which may introduce its own distortions that might possibly swamp any differences. Certainly recording the analog output is prone to (small) variability.
post #10 of 138
I really like this idea , these are the cables id be interested in being compared

lifatec glass cabes
SILFLEX Glass Toslink MiniPlug Digital Audio Optical Cables, ST, Mini Plug, Duplex and Armored

dayton glass cable
Parts-Express.com:*Dayton GOC-3 Glass Optical Digital Cable 3 ft. | toslink optical cable glass optical fiberoptic. digital optical Dolby digital 5.1

ebay glass cable
3' 3 ft GLASS TOSLINK DIGITAL OPTICAL CABLE - Premium - eBay (item 390163917329 end time Mar-30-10 23:00:04 PDT)


When testing the cables that I had, I tested a 10ft glass optical cable from sonicwave, a 6ft mini to toslink from monoprice and a 3ft toslink cable I got with my ibasso D10. For the 3ft and 10ft glass cable I had to use a toslink to mini adapter I got from monoprice to connect them to my macbook pro.
I found that the glass one sounded better than the monoprice cable but the best one of ll three was the 3ft cable, it had the clearest sound and more extended detail of all three. Im now interested in trying out a 3ft glass cable but Im not ure which to get.

A problem Im worried about though is the toslink to mini adapter, since these use plastic they will probably limit the full bandwidth capabilities of a glass cable.
post #11 of 138
Do you have a 30 foot optical cable just for laughs? Also when you realize there's no difference between the cables and become desperate to see a difference, start bending all the cables into circles to try to induce attenuation (careful not to go past bend radius of expensive glass cables).
post #12 of 138
Thread Starter 
Quote:
Originally Posted by Kawai_man View Post
A problem Im worried about though is the toslink to mini adapter, since these use plastic they will probably limit the full bandwidth capabilities of a glass cable.
Plastic has a 5 - 6 mhz bandwidth more than enough for red book, however one could compare two cables from the same stable , one with toslink to mini and the other toslink/toslink with a mini-adaptor ?
post #13 of 138
very nice! but sadly, "measuring" digital audio cables w/ loopback WAVE audio files recordings would be like eating soup w/ a fork...they will all be "bit-perfect" if that can reassure you, and avoid wasting your time and money unnecessarily.

you want to measure the jitter of the stream transport, maybe you could borrow PeterSt's equipment? Measuring XXHighEnd

measuring jitter is indeed rocket science.

some food for thoughts: TOSLINK Interconnect History & Basics
Quote:
An often-overlooked cause of jitter is bandwidth limiting of the digital signal. Quoting from the Rémy Fourré Stereophile article "Jitter and the Digital Interface" published in the October, 1993 issue; " A word about optical links. Still using the example above with digital signals A and B, a low-pass filter at 5MHz-typical of TosLink-causes a time difference of 121ps. A 6MHz low-pass filter causes a time difference of 33ps. For adequate performance, optical links must have a bandwidth of 9MHz minimum. To operate at 48kHz and have a 15% margin for speed adjustments, the interface bandwidth must be at least 11MHz."
anyway, I can see where that project of yours is gonna go...you're gonna post zillions of FFT's and the conclusion will be "ya see, they're all the same to me!"

I would suggest this method to add jitter on purpose: http://www.head-fi.org/forums/f133/h...7/#post6338056

it's said to work w/ coax, you'd have to test beforehand whether it'd work w/ toslink too
post #14 of 138
Isn't the jack internally for toslinks emitter and detector, plastic?
post #15 of 138
Thread Starter 
Quote:
Originally Posted by leeperry View Post

An often-overlooked cause of jitter is bandwidth limiting of the digital signal. Quoting from the Rémy Fourré Stereophile article "Jitter and the Digital Interface" published in the October, 1993 issue; " A word about optical links. Still using the example above with digital signals A and B, a low-pass filter at 5MHz-typical of TosLink-causes a time difference of 121ps. A 6MHz low-pass filter causes a time difference of 33ps. For adequate performance, optical links must have a bandwidth of 9MHz minimum. To operate at 48kHz and have a 15% margin for speed adjustments, the interface bandwidth must be at least 11MHz."
This article bases much of it's maths on Julian Dunn's articles , Dunn never empirically determined audibile jitter levels, it is a model and also based on a 120db signal, this is questionable as a good model...Dunn's writings were in Benjamin and Gannon's bibliography and they used optical links in 1998 to test jitter audibility and they did not find toslink to be a limiting factor see fig 4 on page 4

Quote:
Figure 4 shows the spectrum of jitter measured from a laptop PC DVD ROM with optical output. Excellent performance is achieved despite the use of an optical interface. The jitter spectrum is basically white phase noise jitter with a spectrum level of 7 ps rms and small additional sinusoidal components at 250 Hz and 1.3 kHz.
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