Optical digital interconnects

[tbewick]

Its a generic answer. The distortion of the light signal sent down the optical fibers isnt as great as the signal sent over a digital coax line with added electrical distortion factors also in play, so they say. Sorry I didnt technical geeky, freaky the answer and word it to your liking!!!!

It depends on the quality of the optical or electrical digital cable. Optical cable performance is measured in terms of bandwidth (probably wavelength versus intensity over a certain frequency range) and signal to noise ratio. There are probably other specs that are important as well.

Preferably electrical cable should have bandwidth extending into the MHz region. This helps to prevent jitter, but a good quality DAC should in any case be able to reject jitter. You can measure the quality of the electrical digital signal. If I remember correctly, you feed the signal into an oscilloscope and with some fiddling you get an 'eye pattern'. You can assess the quality of the digital signal using this pattern. The Digital Interface Handbook has some info on this test.

If you wanted to, you could look up the standards specified for the Toslink and electrical S/P-DIF interfaces in a library. That would be very boring and probably pointless because cable manufacturers don't usually give the specifications for their cables. If you really wanted to, you could test the cable performance yourself. Such a measurement would provide more useful information than the usual uncontrolled listening tests of digital cables which some audio reviewers do.

The good thing is that the effect on sound quality should not be significant.

As you said, this is all very geeky and most likely wholly unimportant.
I think things would be much simpler if CD/DVD player manufacturers only provided one socket, either electrical or optical, instead of both. This would stop people having to choose one over the other.

 

[jonnythan]

A calibration DVD is way, way, way better than a total guesstimate.

Get the calibration DVD.

 

[MDS]

MDS, I know this thread has nothing to do with video calibration and I apologize for straying off the topic of discussion, but can you please offer your views on calibration disks for displays ? Like DVE. Are they really "essential" for calibrating displays or are they gimmicks like JAD2 said ?

JAD2's point was that no two dvd players are identical and also that if you calibrate the display using a calibration disc in the dvd player, you have effectively only calibrated the display for the dvd player and those settings may not be correct for other source devices (like say the cable box). All that is true, but in no way makes a calibration disc a 'gimmick'.

- First and foremost, the patterns on the disc are mastered to known color standards and you use them to get the TV to display, as closely as possible, the 'correct' color.

- You CANNOT calibrate your TV by eye until you think it 'looks good' because what you think looks good may not necessarily be correct. For example, people say you should use a very colorful video like Monsters Inc. and just tweak until it looks good to you. The problem with that is you don't know what a monster like Sully looks like in real life (unless maybe you saw one in your bedroom closet when you were a kid. )

So you tweak the color, contrast, and brightness until the monster is a beautiful shade of lime green to your eyes - but the disc was actually mastered with the intent that he appear forest green.

- Newer TVs often allow you to save calibration settings per input. So you can save the settings for the DVD and do the cable box separately (though you need the same patterns to do so and some HD stations transmit them early in the morning). The problem though is that if you are using the receiver as the video switcher with only one cable to the TV then the settings you obtained with the calibration disc will apply to all sources - but they will be pretty damn close to correct unless your dvd player is very poor to begin with.

- You cannot set contrast and brightness by eye. If you think you can you will most likely see 'black crush' where shades of dark gray/black that are supposed to be slightly different actually look the same and the image is too dark with lost detail. Watch any movie with very dark scenes and see if you can easily see the details in the image. IME, this is very hard to get right anyway but the disc does improve things greatly. If your dvd player cannot pass the 'blacker than black' pluge pattern necessary for calibration then buy one that can. It's not fair to say that calibration discs are worthless because some players are poor or cannot pass blacker than black.

All of this stuff is for people who want to get as close to technically correct as possible. I think they are worthwhile (I have both DVE and AVIA).

I agree wholeheartedly with jonnythan that a calibration disc is way better than a total guesstimate.

 

[Jack Hammer]

JAD2's point was that no two dvd players are identical and also that if you calibrate the display using a calibration disc in the dvd player, you have effectively only calibrated the display for the dvd player and those settings may not be correct for other source devices (like say the cable box). All that is true, but in no way makes a calibration disc a 'gimmick'.
...
I agree wholeheartedly with jonnythan that a calibration disc is way better than a total guesstimate.

Do you think the best solution (maybe not cheapest, though) would be to have your tv professionally calibrated (either by purchasing the equipment and doing it yourself or by hiring an outside source)? And then using the test disc to calibrate your dvd player for its optimum performance? Would that be the way to get the best performance and would it really be worth the additional cost?

Jack

 

[JAD2]

First according to the tests performed on DVD players, not many passed the blacker than black levels. So which one do you have would be asked, because if its one than doesnt, well??

Next up is the fact your still using your eyes to judge the levels to the said disc. Unless you know you dont have a color problems, black and white shade problems and your eyes are perfect, would it be correct you setting it.

Then again I'll point out, that most TV's made today and even the so-called creams of the crops cannot correct to near perfect at all its level adjustment range you have to play with. So your doing blacks and whites and out of all the bars given to you a few dont show up no matter how you adjust it!!!! What do you do then???? Call it close enough, but its still incorrect and could be possibly altering the other spectrum's. Unless you can get into the service menu and if you could can you safely actually say YOU KNOW WHAT YOUR DOING, could you correct it.

Now all the settings effect all the other ones showing. So once your done and you think you got it right, you go over it again and find out changing one altered the other and you do it again and again and again. Then on top of that you may not like what you set, something just isnt right to your taste and you drive that one higher and or lower, which now changes it again. Never ending battle, you'll drive yourself nuts trying to perfect it. Wont happen unless you actually believe!!!!! And most do!!!!


Now its said time is money, OK!!!
How much of this time and actual money are you going to spend on interconnects, discs and all that other stuff???

Mr. ISF tech for a few hundred, WILL make it as close to perfect as it can be!!! You'll never achieve his level, not even close!!

Been there, did it, went nuts, thought it was dam good , but after Mr. ISF tech left, I said GIMMICK to disc's!!!!

 

[billy p]

Well

to me if I must contend with all the extra cost for equipment and discs to fine tune my set for every input source I'm better off paying a pro to calibrate it. Laying out a bunch of money and doing it myself and not getting the best results is a waste of time and money so I would agree with Jad2 pay the tech and be done with it .
Also it's a PITA anyways

 

[mtrycrafts]

JAD2's point was that no two dvd players are identical and also that if you calibrate the display using a calibration disc in the dvd player, you have effectively only calibrated the display for the dvd player and those settings may not be correct for other source devices (like say the cable box). All that is true, but in no way makes a calibration disc a 'gimmick'.

- First and foremost, the patterns on the disc are mastered to known color standards and you use them to get the TV to display, as closely as possible, the 'correct' color.

- You CANNOT calibrate your TV by eye until you think it 'looks good' because what you think looks good may not necessarily be correct. For example, people say you should use a very colorful video like Monsters Inc. and just tweak until it looks good to you. The problem with that is you don't know what a monster like Sully looks like in real life (unless maybe you saw one in your bedroom closet when you were a kid. )

So you tweak the color, contrast, and brightness until the monster is a beautiful shade of lime green to your eyes - but the disc was actually mastered with the intent that he appear forest green.

- Newer TVs often allow you to save calibration settings per input. So you can save the settings for the DVD and do the cable box separately (though you need the same patterns to do so and some HD stations transmit them early in the morning). The problem though is that if you are using the receiver as the video switcher with only one cable to the TV then the settings you obtained with the calibration disc will apply to all sources - but they will be pretty damn close to correct unless your dvd player is very poor to begin with.

- You cannot set contrast and brightness by eye. If you think you can you will most likely see 'black crush' where shades of dark gray/black that are supposed to be slightly different actually look the same and the image is too dark with lost detail. Watch any movie with very dark scenes and see if you can easily see the details in the image. IME, this is very hard to get right anyway but the disc does improve things greatly. If your dvd player cannot pass the 'blacker than black' pluge pattern necessary for calibration then buy one that can. It's not fair to say that calibration discs are worthless because some players are poor or cannot pass blacker than black.

All of this stuff is for people who want to get as close to technically correct as possible. I think they are worthwhile (I have both DVE and AVIA).

I agree wholeheartedly with jonnythan that a calibration disc is way better than a total guesstimate.

I do need to add that a DVD player has its own issues of reproducing video accurately or not; most don't. Then, some almost have as many adjustments on them as a TV. If the DVD player is not passing perfect video, it will not pass that perfect calibration video perfectly either.
There are two variables of unknown quantity here, TV and DVD player. The disc is a known standard
If, a known standard could be sent to the TV via computer feed, then the TV set can be calibrated to its max capability. Then, the DVD player can be also calibrated with that disc to its max capability.
If you calibrate the TV with an unknown quality of player, that TV will be at is max performance for DVD playback. but maybe not with other video sources, like the cable box video.

 

[mtrycrafts]

Do you think the best solution (maybe not cheapest, though) would be to have your tv professionally calibrated (either by purchasing the equipment and doing it yourself or by hiring an outside source)? And then using the test disc to calibrate your dvd player for its optimum performance? Would that be the way to get the best performance and would it really be worth the additional cost?

Jack

In my opinion, that depends on how much you value the max performance from a good TV. The disc vill not let you calibrate without other instruments. In no way can you calibrate gray scale. proper color setting for the 6 colors, yes, the primary and secondary too. Perhaps it may not let you properly set 6500K. But, without the extra tools you can still do a pretty good job.
Some pro ISF calibration is reasonably priced

 

[dominic42]

a good article that i found educational.
http://www.impactacoustics.com/links/optical_interconnect_basics.html?

and maybe you guys can answer a question:
i switched from anolog to toslink on my cable box to the reciever and the volume increased by three times why is this?

 

[MDS]

and maybe you guys can answer a question:
i switched from anolog to toslink on my cable box to the reciever and the volume increased by three times why is this?

Cable channels on 'digital cable' broadcast both analog and digital signals at the same time and the digital audio is almost always at a higher average level than the analog - hence it is louder. This is most easily observed on the Music Choice channels where the analog feed is so low it is often barely audible and the digital feed is much louder.

Incidentally this is why receivers have 'auto' settings that detect whether a digital or analog signal is available and automatically switch to the digital when it is present. That way when you change from a channel that has digital audio to one that has only analog audio, the receiver does the switching for you so you don't have to change the settings from digital to analog manually. That feature is a requirement if you have digital cable because everyone knows that many of the channels on 'digital cable' still have analog audio.