Digital Coaxial vs Optical Toslink

[Eug]

Originally posted by: TastesLikeChicken
There are valid arguments for both sides of this issue. Theoretically, digital coax does have some advantages over TOS transmission since there's no digital to optical conversion. It also has some drawbacks, such as the potential for ground-loops.

Yep, and IMO this is a HUGE drawback of coaxial, and obviously much more so than any theoretical jitter arguments.

I've encountered ground-loops before using coaxial. It doesn't happen very often, but when it does, it's very, very, very irritating. Ground loops are obviously not an issue with optical.

The main drawback of optical IMO is simply the cables. Longer optical cables can be problematic, they aren't as flexible as copper wire, and optical cables may cost more.

Actually, scratch that last point. In 2007, if you're going cheap, you're actually better off going with a cheap optical cable than a cheap coax cable IMO. The cheap coax cables often have poor shielding --> higher risk of ground loops. Oh and scratch the second last point too. Well-shielded coaxial cables aren't that flexible either.

In regards to audible differences, no blind tests have ever been able to establish that people can hear a difference between the two, even when people who claim to be able to detect a difference are used. The only real difference is apparent when the people tested know what type of transmission mode is being used in advance, which would imply that any audible difference is psychological in nature and not truly perceptive.

Yup. The "golden ears" effect.

The weird part is for those "golden ears" it should be moot anyway, since they should probably be using HDMI and lossless, or else analogue outputs.

 

[Auric]

There's more variety of coaxial cable. Flexibility isn't a problem beyond the cheapest "CATV" schtuff. One of the main advantages is being able to make your own so easiliy with a wide variety of both cable and connectors and likewise being able to modify them on a whim. The same schtuff can also be used for video, audio, and powered subs. 'nutha advantage is durability versus fiber.

 

[alfa147x]

Ok so what are ground loops?

 

[TVNoob]

Am I missing something here? Surely with digital tranmission there shoudl not be any interference from other signals?

The ground loop effect would not affect co-axial cables unless it completely destroyed the signal to such an extent the 1's and 0's could not be determined at the receiver?

You won't get the same sort of effect as you do in analogue transmission where the signal can be modified slightly by inference and the resulting different in voltage/frequency will actually effect the signal at the speaker. With digital, as long as your 1's and 0's are not lost in the cable then the receiver will do it's D>A and squirt it out the speaker.

Wouldnt there be redundant coding & error checking in digital signals too?

 

[spidey07]

Originally posted by: TVNoob
Am I missing something here? Surely with digital tranmission there shoudl not be any interference from other signals?

The ground loop effect would not affect co-axial cables unless it completely destroyed the signal to such an extent the 1's and 0's could not be determined at the receiver?

You won't get the same sort of effect as you do in analogue transmission where the signal can be modified slightly by inference and the resulting different in voltage/frequency will actually effect the signal at the speaker. With digital, as long as your 1's and 0's are not lost in the cable then the receiver will do it's D>A and squirt it out the speaker.

Wouldnt there be redundant coding & error checking in digital signals too?

Of course there is interference, there always is. But that's not the problem.

It's not a question of 1s or 0s because keep in mind that digital is analog. It's just a state change. But the transition from 0 to 1 is not instantaneous and never will be. This is where the bandwidth of a cable comes into play and jitter shows up. Not really from the cable per say, but from the transmitter and receiver because there is no common clock.

A cable doesn't lose information, it changes it. How the transmitter and receiver deal with this is the point. With such a low bandwidth, TOSlink is more prone to jitter.

 

[montypythizzle]

They are not the same!!! Use Monster Cable and you guys can definitely tell the difference, no joke. I did a double blind test between the two and they sounded different using crappy Monoprice cables and sounded the same using Monster Cable.

 

[TVNoob]

Originally posted by: spidey07
It's not a question of 1s or 0s because keep in mind that digital is analog. It's just a state change. But the transition from 0 to 1 is not instantaneous and never will be. This is where the bandwidth of a cable comes into play and jitter shows up. Not really from the cable per say, but from the transmitter and receiver because there is no common clock.

This doesn't make sense to me.

Of course there is a state change, but if there is no common clock then the receiver must be keeping it's own time and applying the received 1's and 0's on this clock. So any noise around the state change would have to be enough to delay a whole period for the receiver to mis-receive it.

Additionally, I would expect redundant error correction in the encoded signal so it could cope with this. Surely in 2007 the latest digital protocols are designed to cope with trivial stuff like this.

 

[TVNoob]

The weird part is for those "golden ears" it should be moot anyway, since they should probably be using HDMI and lossless, or else analogue outputs.

Are you implying there is a difference between the digitally encoded sound signal on HDMI (lossless) and the digitally encoded sound signal on co-ax? I don't think this is true.

 

[PurdueRy]

Originally posted by: TVNoob

The weird part is for those "golden ears" it should be moot anyway, since they should probably be using HDMI and lossless, or else analogue outputs.

Are you implying there is a difference between the digitally encoded sound signal on HDMI (lossless) and the digitally encoded sound signal on co-ax? I don't think this is true.

the only way to get the lossless audio formats is via analog 5.1/6.1/7.1 connections or HDMI. They can't be transmitted via digital coax or optical.

 

[vi edit]

Originally posted by: TVNoob

The weird part is for those "golden ears" it should be moot anyway, since they should probably be using HDMI and lossless, or else analogue outputs.

Are you implying there is a difference between the digitally encoded sound signal on HDMI (lossless) and the digitally encoded sound signal on co-ax? I don't think this is true.

I'm trying to find the links/references but failing at teh google...

I'm pretty sure that *technically* HDMI can carry the new uncompressed audio formats on Blu-Ray/HD-DVD without altering them. Optical will introduce some compression.

That being said, I honestly have no idea if your average person, on an a typical home theater setup would ever be able to tell the difference.

 

[spidey07]

Originally posted by: TVNoob

Originally posted by: spidey07
It's not a question of 1s or 0s because keep in mind that digital is analog. It's just a state change. But the transition from 0 to 1 is not instantaneous and never will be. This is where the bandwidth of a cable comes into play and jitter shows up. Not really from the cable per say, but from the transmitter and receiver because there is no common clock.

This doesn't make sense to me.

Of course there is a state change, but if there is no common clock then the receiver must be keeping it's own time and applying the received 1's and 0's on this clock. So any noise around the state change would have to be enough to delay a whole period for the receiver to mis-receive it.

Additionally, I would expect redundant error correction in the encoded signal so it could cope with this. Surely in 2007 the latest digital protocols are designed to cope with trivial stuff like this.

Of course they are. But what are you going to do if a frame is errored - it's a one way transmission constrained by time.

It sounds like you understand EE so I'll ask a simple question - what is the limiting factor to the bandwidth of a cable ? Think time.

 

[TVNoob]

the only way to get the lossless audio formats is via analog 5.1/6.1/7.1 connections or HDMI. They can't be transmitted via digital coax or optical.

Can you explain what the difference is between digital coax/digital optical and HDMI?

Are far as I understand it, the digital audio signal squirted down HDMI is the same as the one squirted down the coax/fibre cables?

 

[PurdueRy]

Originally posted by: TVNoob

the only way to get the lossless audio formats is via analog 5.1/6.1/7.1 connections or HDMI. They can't be transmitted via digital coax or optical.

Can you explain what the difference is between digital coax/digital optical and HDMI?

Are far as I understand it, the digital audio signal squirted down HDMI is the same as the one squirted down the coax/fibre cables?

its copyright protection. HDMI is simply the only form that players are allowed to transmit the HD audio formats over(besides 5.1/6.1/7.1 analog). It's not necessarily a limitation of the cable...but a restriction imposed by those who think it will stop people from copying the material.

 

[vi edit]

Originally posted by: PurdueRy

Originally posted by: TVNoob

the only way to get the lossless audio formats is via analog 5.1/6.1/7.1 connections or HDMI. They can't be transmitted via digital coax or optical.

Can you explain what the difference is between digital coax/digital optical and HDMI?

Are far as I understand it, the digital audio signal squirted down HDMI is the same as the one squirted down the coax/fibre cables?

its copyright protection. HDMI is simply the only form that players are allowed to transmit the HD audio formats over(besides 5.1/6.1/7.1 analog). It's not necessarily a limitation of the cable...but a restriction imposed by those who think it will stop people from copying the material.

Is it all formats(True-HD, DTS-MA) or just PCM? And from I read, 2 channel PCM will go across, but the 5.1 and 7.1 won't.

 

[TVNoob]

its copyright protection. HDMI is simply the only form that players are allowed to transmit the HD audio formats over(besides 5.1/6.1/7.1 analog). It's not necessarily a limitation of the cable...but a restriction imposed by those who think it will stop people from copying the material.

I understand - so this is only an issue for dts®-ES and Dolby® Digital EX ?

What you describe makes sense if this is the case. I don't think DTS or DD5.1 suffer from this issue as they were standards before HDMI?

So to clarify this discussion - the loss of quality using digital coax instead of HDMI has nothing to do with signal interference or bandwidth and everything to do with those two formats being locked down so they will only work on content protected links

 

[YOyoYOhowsDAjello]

Originally posted by: TVNoob

its copyright protection. HDMI is simply the only form that players are allowed to transmit the HD audio formats over(besides 5.1/6.1/7.1 analog). It's not necessarily a limitation of the cable...but a restriction imposed by those who think it will stop people from copying the material.

I understand - so this is only an issue for dts®-ES and Dolby® Digital EX ?

What you describe makes sense if this is the case. I don't think DTS or DD5.1 suffer from this issue as they were standards before HDMI?

So to clarify this discussion - the loss of quality using digital coax instead of HDMI has nothing to do with signal interference or bandwidth and everything to do with those two formats being locked down so they will only work on content protected links

We're talking about Dolby True HD and DTS HD

http://www.dolby.com/promo/hd/trueHD.html
http://www.dtsonline.com/dts-hd/

Not DD-EX / DTS-ES

 

[TVNoob]

Originally posted by: spidey07

Of course they are. But what are you going to do if a frame is errored - it's a one way transmission constrained by time.

It sounds like you understand EE so I'll ask a simple question - what is the limiting factor to the bandwidth of a cable ? Think time.

I think a question more germaine to this discussion is whether there is any sort of bandwidth limitation sending digital audio down co-axial cable.. and the answer is is big fat no. The signal isn't anywhere near constrained by the bandwidth of the medium.

By the way, you don't seem to be clear on what the word REDUNDANT means in terms of a redundant encoding algorithm.... it allows the receiver to piece back the signal even if parts of it are lost. So there is no need to re-request the packet (are you sure you're not confusing this with TCP/IP!) as the information has already been sent to allow for correct of transmission errors (redundant information)

 

[TVNoob]

We're talking about Dolby True HD and DTS HD

http://www.dolby.com/promo/hd/trueHD.html
http://www.dtsonline.com/dts-hd/

Not DD-EX / DTS-ES

Got it - so the point about

"the loss of quality using digital coax instead of HDMI has nothing to do with signal interference or bandwidth and everything to do with those two formats being locked down so they will only work on content protected links "

is correct, for Dolby True HD and DTS HD ? But DD-EX / DTS-ES will sound idential whether played over HDMI or digital co-ax ?

 

[YOyoYOhowsDAjello]

Originally posted by: TVNoob

We're talking about Dolby True HD and DTS HD

http://www.dolby.com/promo/hd/trueHD.html
http://www.dtsonline.com/dts-hd/

Not DD-EX / DTS-ES

Got it - so the point about

"the loss of quality using digital coax instead of HDMI has nothing to do with signal interference or bandwidth and everything to do with those two formats being locked down so they will only work on content protected links "

is correct, for Dolby True HD and DTS HD ? But DD-EX / DTS-ES will sound idential whether played over HDMI or digital co-ax ?

Yeah, that's my understanding of it.

 

[biggestmuff]

Originally posted by: PurdueRy

Originally posted by: migo
than with...

I'm talking about the normal cables that you get with most speaker systems. Every time I place a call or get an incoming call I can hear it ahead of time on my speakers since the cable picks up the signal. That's mainly dependent on the length of the cable from what I understand. Are S/PDIF coax cables shielded in such a way that this doesn't occur?

not likely to happen. With analog cables any signal induced into the cable WILL be played out the speakers. With a digital connection you have to induce a 1 or a 0...which is fairly hard to do.

Unless balanced cables are used.

Originally posted by: PurdueRy

Originally posted by: migo
Thanks. That makes perfect sense.

Another option is to buy shielded 3.5mm cables. I believe most 3.5mm cables that come with speakers sets aren't shielded...or at least not well. This makes them perfect antennas.

Grounding both ends would make a perfect antenna.

 

[PurdueRy]

Originally posted by: biggestmuff

Originally posted by: PurdueRy

Originally posted by: migo
than with...

I'm talking about the normal cables that you get with most speaker systems. Every time I place a call or get an incoming call I can hear it ahead of time on my speakers since the cable picks up the signal. That's mainly dependent on the length of the cable from what I understand. Are S/PDIF coax cables shielded in such a way that this doesn't occur?

not likely to happen. With analog cables any signal induced into the cable WILL be played out the speakers. With a digital connection you have to induce a 1 or a 0...which is fairly hard to do.

Unless balanced cables are used.

Originally posted by: PurdueRy

Originally posted by: migo
Thanks. That makes perfect sense.

Another option is to buy shielded 3.5mm cables. I believe most 3.5mm cables that come with speakers sets aren't shielded...or at least not well. This makes them perfect antennas.

Grounding both ends would make a perfect antenna.

I am not aware of any computer speaker systems that have balanced inputs. So balanced cables have no bearing on his situation.

As for the antenna, grounding both ends wouldn't make much of an antenna with a purpose.

 

[Eug]

Originally posted by: TVNoob
Am I missing something here? Surely with digital tranmission there shoudl not be any interference from other signals?

The ground loop effect would not affect co-axial cables unless it completely destroyed the signal to such an extent the 1's and 0's could not be determined at the receiver?

I think you're missing the point.

I've had the (admittedly infrequent) situation where plugging in the coaxial cable introduced hum in the system. It had nothing to do with the digital transmission per se. The DVD player could be completely off and the hum was still there, and was only removed by unplugging the coax digital cable.

Granted, at the time I had only a lower mid-end receiver, and lots of poorly shielded cables, but nonetheless the problem existed with coaxial digital. This type of problem simply doesn't exist with optical.

 

[JAG87]

Originally posted by: Eug

Originally posted by: TVNoob
Am I missing something here? Surely with digital tranmission there shoudl not be any interference from other signals?

The ground loop effect would not affect co-axial cables unless it completely destroyed the signal to such an extent the 1's and 0's could not be determined at the receiver?

I think you're missing the point.

I've had the (admittedly infrequent) situation where plugging in the coaxial cable introduced hum in the system. It had nothing to do with the digital transmission per se. The DVD player could be completely off and the hum was still there, and was only removed by unplugging the coax digital cable.

Granted, at the time I had only a lower mid-end receiver, and lots of poorly shielded cables, but nonetheless the problem existed with coaxial digital. This type of problem simply doesn't exist with optical.

exactly, its called 60 Hz hum, and I cant believe it took 4 pages to bring this up.

 

[Rubycon]

You're hearing a hum because there is a difference in the ground potential between connected components. This is called a ground loop.

Optical has electrical advantages however in the case with consumer SPDIF TOSLINK connected devices time domain errata can cause serious playback implications where there is no clock sync. The quality of the optoelectronic conversion (as there are no truly optical DAC/ADC components) will ultimately determine the sound quality in playback equipment chains using this method.

 

[destrekor]

besides ground loop acting as a major issue with digital coax, the other issue I am also familiar with is the interference. however, I don't know the nature of the data.. is it anything similar to networking and is there a built-in 'checksum', so to speak, for audio codecs? Are there still frames of data, maybe even packets? I ask about the checksum/build in error checking/correction, because severe interference can cause a loss of 1's or 0's. Normally the hardware receiving the data can also detect whether a badly-formed 1 or 0 is indeed a 1 or 0, but that all depends on the degree of differential. If a 1 is lowered enough, it could appear to be a noisy 0. Think of it this way, if severe noise is introduced on the line in place of a 0, it may reach, say, .5.. the receiver is likely to treat that .5 as a 0 still, but what if a 1 approaches the same level at a different point in time, is it going to be dropped and replaced with a 0? Is there built in computations for error checking to determine if a 1 or 0 was lost somewhere in transmission due to noise/interference? During CCNA training I remember a lot of this, however I have also lost some knowledge due to never taking the CCNA test or getting certified due to my lack of interest once I graduated highschool. And I also have no knowledge of the data packaging for audio codecs in digital transmission.