A friend of mine is a bit of an audiophile (always strikes me as a bit of a Nasty Description, that, not too distantly related to other kinds of 'philes, but I digress). He's worked in the sound and home entertainment industry for many years and with a lot of stuff he really sounds like he knows what he's talking about and I appreciate his opinion. However the other day he was talking about some $120 TOSLINK cables, and was telling us How Much Better they sounded. I laughed and said he must be joking, that digital data transmitted optically either gets there or it doesn't – spending more than $15 on a standard link TOSLINK is an absolute waste of money. He disagreed and said that with a lower quality cable you can lose data that is repaired with error correction, resulting in poorer sound.
Now correct me if I'm wrong, but if you're listening to a CD (or audio DVD) and you lose data bits, somehow, due to a "lower quality" cable, don't you end up with clicks, pops or a complete absence of sound, depending on your equipment and how it handles the data loss? AFAI was aware, with digital media you're either getting the whole data stream, or if it becomes unsynced or corrupt there is NO question about it. Am I totally off track here, or does my friend need a refresher course in digital media connectivity solutions?
It seems to me that audio is an industry where there's a lot more voodoo going on and a lot less science. Personally I find that a bit confusing - being a tech industry, I would have thought the people in it would DEMAND scientific evidence and justification. I mean, sound in all its forms is measurable well beyond what the human ear can perceive - why don't we have labs with audiometers testing scientifically whether cable A improves the sound quality over cable B etc? Why isn't there an audio website with a central, seachable database that proves and debunks various voodoo cable/speaker/amplifier/wooden volume knob myths?
A friend of mine once connected the demo speakers in a sound lab up to the secondary channel from the amplifier using 500m rolls of EXTREMELY cheap cable (you know, your 4c a metre rubbish that ships with $15 car speakers). Yes, that's 500m rolls for EACH speaker, and he said you couldn't tell the difference between that and the $400/m 3m cable that was connected on the primary channel. He demonstrated it in a blinded test to all the sales guys there too, and they couldn't believe it. Its an example that's sold me - I know enough not to buy cable that can't handle the current you're trying to pass through it, but I'll buy a $50 cable over a $400 one if they both do the job any day!
Trevor
Answer:
Your friend's error correction idea is an excellent theory, with only two minor flaws.
One, PCM digital audio streams don't have any error correction, and two, PCM digital audio streams don't have any error correction. Now I realise that technically speaking that's only one flaw, but I thought that it was such a big one that it was worth mentioning twice.
There's error correction on CDs, and I don't know the details of error correction for the compressed movie audio formats, but it's important to remember that error correction in the disc reader is separate from error correction (if any) in the digital data link from the reader to the separately-boxed decoder/DAC.
In the case of a CD player feeding a digital interconnect, the player does its best to get the right bits - or, at least, inoffensively interpolated bits - off the disc, but after that the data's on its own.
If your digital connection's dropping bits then it certainly can affect the sound of the system, but, as you say, it's rare for a digital interconnect to be less than perfect in such a way as to make an audible difference, without that audible difference to be that there just isn't any music any more, or at least that the music's cutting out and/or hideously distorted. That's the nature of digital data - it's generally either perfect, or very obviously broken. It doesn't handle data loss as elegantly as analogue.
At this point, audiophiles usually launch into an explanation involving detection thresholds and clock jitter and so on and so forth, but that's irrelevant too, because it's all stuff that happens before, or after, the cable. All the cable has to do is move the bits; all it can do to them on the way is attenuate the signal somewhat.
Attenuation can be significant for optical cables once the cable starts getting pretty long. There are various factors to consider then, and cheap TOSLINK cables have a plastic lightguide, which is no good for cable runs of more than a few metres - actually, I can believe that the very cheapest ones could start crapping out at rather shorter lengths. Cheap and nasty cables are also more prone to connector or lightguide damage if they're not treated very carefully - which they may not have been by the person who put 'em in the box at the factory, for all you know.
Digital audio isn't a very demanding task anyway. Since even maximum bit rate DTS audio - which may or may not be used on any DVDs - only needs 1536 kilobits per second (a bit more than the data rate of uncompressed CD audio), and most DVDs require less than a third of that data rate, for regular digital audio cable runs of a foot or two you can pretty much use a piece of clean string.
On the subject of the demand, or lack thereof, for science in the consumer audio industry - I'm sure some of the companies involved care about it a great deal. But industries have customers, and it's their demand, as steered by the shadowless blank-eyed man-things with marketing degrees, that drives the product development decisions. Since psychoacoustic factors are powerful, and the audio reproduction industry long since passed the point where most listeners cannot actually be more satisfied with the sound of the system, the manufacturers were forced to move into less quantifiable factors, whether those factors actually existed or not.
Some of the further development has been very worthwhile. The continuing advances in portable players and headphones, cheap-ish car stereos and boom boxes that can play MP3 CDs, user interface improvements, multi-room audio and so on. And bells and whistles qualify, as well; I'm not a fan of mini systems with indifferent sound and a million blinking lights, but if someone likes the idea of a Starship Enterprise stereo and is happy enough with the sound, then good luck to them.
But real advances only go so far, while the ability of human beings to fool themselves is pretty much limitless. I'm sure that some of the hi-fi snake oil merchants know they're scam artists, but justify their activities on the grounds that gullible people with fat wallets are going to spend their money on some damn thing they don't need. If the "audiophiles" were going to give the money to charity, they would have already. They'll probably get more joy out of a pile of hi-fi crap than they would out of an obscure supercar that spends 96% of its life in the shop, and it's not as if hi-fi scammers are robbing the poor.
Well, that's how I'd justify it if I were in that business, anyway.
Why isn't there a site with a database of reviews of goofy hi-fi tweaks? Because snake oil enthusiasts reject empirical testing, preferring a heady mix of faux skepticism and self-important subjectivism. They're unsinkable rubber ducks, like a lot of believers in the paranormal; the ad hoc explanations flow thick and fast when countervailing evidence is presented.
Anyone who wanted to run a site like the one you suggest would have to pay an awful lot of money for voodoo devices to test, since it's not as if he'd get free review product (well, not after he put the first few reviews up, anyway...). He'd also have a dickens of a time finding anyone willing to advertise on the site - the makers of Acme Medium Duty Figure 8 Bell Wire, "Just as good as Monster Cable!", probably aren't too interested in selling speaker-cable lengths of their stuff at a buck profit per unit, even if audiophiles can be talked into buying it instead of electrically-identical-at-audio-frequencies stuff that makes its manufacturers a thousand bucks per unit.
And, on top of that, such a site would be boring to run. How many double blind tests that end up supporting the null hypothesis would you like to organise per week?
On the one hand, at least the audiophile nuts aren't likely to declare holy war on anyone about the directionality of cables or how much better CDs sound after you've frozen them. But, on the other, he who's happy to believe one crazy thing for no reason is likely to be happy to believe another; the frequently heard "Where's the harm?" argument falls down there, as it can be argued that all irrational beliefs, no matter how apparently innocuous, help to pollute the world with yet more nonsense and make the truth about anything harder to find.
I'll restrict myself to only one James Randi link, at this point.
Copied and pasted from here http://www.dansdata.com/danletters158.htm
Rintek
Now correct me if I'm wrong, but if you're listening to a CD (or audio DVD) and you lose data bits, somehow, due to a "lower quality" cable, don't you end up with clicks, pops or a complete absence of sound, depending on your equipment and how it handles the data loss? AFAI was aware, with digital media you're either getting the whole data stream, or if it becomes unsynced or corrupt there is NO question about it. Am I totally off track here, or does my friend need a refresher course in digital media connectivity solutions?
It seems to me that audio is an industry where there's a lot more voodoo going on and a lot less science. Personally I find that a bit confusing - being a tech industry, I would have thought the people in it would DEMAND scientific evidence and justification. I mean, sound in all its forms is measurable well beyond what the human ear can perceive - why don't we have labs with audiometers testing scientifically whether cable A improves the sound quality over cable B etc? Why isn't there an audio website with a central, seachable database that proves and debunks various voodoo cable/speaker/amplifier/wooden volume knob myths?
A friend of mine once connected the demo speakers in a sound lab up to the secondary channel from the amplifier using 500m rolls of EXTREMELY cheap cable (you know, your 4c a metre rubbish that ships with $15 car speakers). Yes, that's 500m rolls for EACH speaker, and he said you couldn't tell the difference between that and the $400/m 3m cable that was connected on the primary channel. He demonstrated it in a blinded test to all the sales guys there too, and they couldn't believe it. Its an example that's sold me - I know enough not to buy cable that can't handle the current you're trying to pass through it, but I'll buy a $50 cable over a $400 one if they both do the job any day!
Trevor
Answer:
Your friend's error correction idea is an excellent theory, with only two minor flaws.
One, PCM digital audio streams don't have any error correction, and two, PCM digital audio streams don't have any error correction. Now I realise that technically speaking that's only one flaw, but I thought that it was such a big one that it was worth mentioning twice.
There's error correction on CDs, and I don't know the details of error correction for the compressed movie audio formats, but it's important to remember that error correction in the disc reader is separate from error correction (if any) in the digital data link from the reader to the separately-boxed decoder/DAC.
In the case of a CD player feeding a digital interconnect, the player does its best to get the right bits - or, at least, inoffensively interpolated bits - off the disc, but after that the data's on its own.
If your digital connection's dropping bits then it certainly can affect the sound of the system, but, as you say, it's rare for a digital interconnect to be less than perfect in such a way as to make an audible difference, without that audible difference to be that there just isn't any music any more, or at least that the music's cutting out and/or hideously distorted. That's the nature of digital data - it's generally either perfect, or very obviously broken. It doesn't handle data loss as elegantly as analogue.
At this point, audiophiles usually launch into an explanation involving detection thresholds and clock jitter and so on and so forth, but that's irrelevant too, because it's all stuff that happens before, or after, the cable. All the cable has to do is move the bits; all it can do to them on the way is attenuate the signal somewhat.
Attenuation can be significant for optical cables once the cable starts getting pretty long. There are various factors to consider then, and cheap TOSLINK cables have a plastic lightguide, which is no good for cable runs of more than a few metres - actually, I can believe that the very cheapest ones could start crapping out at rather shorter lengths. Cheap and nasty cables are also more prone to connector or lightguide damage if they're not treated very carefully - which they may not have been by the person who put 'em in the box at the factory, for all you know.
Digital audio isn't a very demanding task anyway. Since even maximum bit rate DTS audio - which may or may not be used on any DVDs - only needs 1536 kilobits per second (a bit more than the data rate of uncompressed CD audio), and most DVDs require less than a third of that data rate, for regular digital audio cable runs of a foot or two you can pretty much use a piece of clean string.
On the subject of the demand, or lack thereof, for science in the consumer audio industry - I'm sure some of the companies involved care about it a great deal. But industries have customers, and it's their demand, as steered by the shadowless blank-eyed man-things with marketing degrees, that drives the product development decisions. Since psychoacoustic factors are powerful, and the audio reproduction industry long since passed the point where most listeners cannot actually be more satisfied with the sound of the system, the manufacturers were forced to move into less quantifiable factors, whether those factors actually existed or not.
Some of the further development has been very worthwhile. The continuing advances in portable players and headphones, cheap-ish car stereos and boom boxes that can play MP3 CDs, user interface improvements, multi-room audio and so on. And bells and whistles qualify, as well; I'm not a fan of mini systems with indifferent sound and a million blinking lights, but if someone likes the idea of a Starship Enterprise stereo and is happy enough with the sound, then good luck to them.
But real advances only go so far, while the ability of human beings to fool themselves is pretty much limitless. I'm sure that some of the hi-fi snake oil merchants know they're scam artists, but justify their activities on the grounds that gullible people with fat wallets are going to spend their money on some damn thing they don't need. If the "audiophiles" were going to give the money to charity, they would have already. They'll probably get more joy out of a pile of hi-fi crap than they would out of an obscure supercar that spends 96% of its life in the shop, and it's not as if hi-fi scammers are robbing the poor.
Well, that's how I'd justify it if I were in that business, anyway.
Why isn't there a site with a database of reviews of goofy hi-fi tweaks? Because snake oil enthusiasts reject empirical testing, preferring a heady mix of faux skepticism and self-important subjectivism. They're unsinkable rubber ducks, like a lot of believers in the paranormal; the ad hoc explanations flow thick and fast when countervailing evidence is presented.
Anyone who wanted to run a site like the one you suggest would have to pay an awful lot of money for voodoo devices to test, since it's not as if he'd get free review product (well, not after he put the first few reviews up, anyway...). He'd also have a dickens of a time finding anyone willing to advertise on the site - the makers of Acme Medium Duty Figure 8 Bell Wire, "Just as good as Monster Cable!", probably aren't too interested in selling speaker-cable lengths of their stuff at a buck profit per unit, even if audiophiles can be talked into buying it instead of electrically-identical-at-audio-frequencies stuff that makes its manufacturers a thousand bucks per unit.
And, on top of that, such a site would be boring to run. How many double blind tests that end up supporting the null hypothesis would you like to organise per week?
On the one hand, at least the audiophile nuts aren't likely to declare holy war on anyone about the directionality of cables or how much better CDs sound after you've frozen them. But, on the other, he who's happy to believe one crazy thing for no reason is likely to be happy to believe another; the frequently heard "Where's the harm?" argument falls down there, as it can be argued that all irrational beliefs, no matter how apparently innocuous, help to pollute the world with yet more nonsense and make the truth about anything harder to find.
I'll restrict myself to only one James Randi link, at this point.
Copied and pasted from here http://www.dansdata.com/danletters158.htm
Rintek
Ah, the SPDIF-cable war ! 
I once also thought that this is complete nonsense. Well, this error correction is nonsense... It takes a lot to loose bits in a digital stream, easy to verify. Take a cheap cable for spdif and play a DTS/DD stream through it. As this is packed data, it can't tolerate single bits lost and you get completely dropped frames. I made that with a 10meter standard RCA-cable, no problems.
BUT, there is the jitter problem, there are spdif receivers without reclock, using the clock provided by spdif. In these cases you need the highest quality cable possible (>100$), as not only digital data is transfered, also the clock for DA conversion. Or, you have a 5$ reclocking device...
Have you ever heard of high quality modem cables for better sounding mp3s ?
Mike
I once also thought that this is complete nonsense. Well, this error correction is nonsense... It takes a lot to loose bits in a digital stream, easy to verify. Take a cheap cable for spdif and play a DTS/DD stream through it. As this is packed data, it can't tolerate single bits lost and you get completely dropped frames. I made that with a 10meter standard RCA-cable, no problems.BUT, there is the jitter problem, there are spdif receivers without reclock, using the clock provided by spdif. In these cases you need the highest quality cable possible (>100$), as not only digital data is transfered, also the clock for DA conversion. Or, you have a 5$ reclocking device...
Have you ever heard of high quality modem cables for better sounding mp3s ?
Mike
Just for comparison DVB from satelite gets lower than 10^-11 BER.
What's the problem with audio bit stream with cable then?
It seems, that it would be a great business introducing all these CRC, convolutional encoding, Reed-Salomon encoding and so on to SPDIF. Audiphiles would probably appreciate one bit error for a month.
What's the problem with audio bit stream with cable then?
It seems, that it would be a great business introducing all these CRC, convolutional encoding, Reed-Salomon encoding and so on to SPDIF. Audiphiles would probably appreciate one bit error for a month.
analog_sa said:
Or, doesn't work, in this case!
Has anyone had a look at the jitter spec of the TOSLINK receiver? Terrible stuff, so I think even if you have an expensive optical cable there, the receiver will just fuzz up the timing...
How difficult is it to build a low-jitter coax interface to replace the TOSLINK? Seems there's a lot of science and voodoo associated with the isolation transformers needed for it...
Cheers!
Clem
Define "difficult"... http://sound.westhost.com/project85.htm
A simple DAC, using the crystal spdif receiver containing reclock. With reclocking spdif becomes what it should be, a simple transfer of digital data...
Mike
A simple DAC, using the crystal spdif receiver containing reclock. With reclocking spdif becomes what it should be, a simple transfer of digital data...
Mike
I used to use Toslink receivers for data communications years ago. The problem is that the rise and fall times are not equal and very signal level dependant, actually too much signal is very bad. Different cables are going to have various losses so the pulse width distortion, which in turn causes recovered clock jitter, will vary.
One side effect of this is that the cable dress (bends cause extra loss) will have an effect on the jitter.
If you are actually getting bit errors on a fibre optic link something is very wrong.
Coax links are much better, and using a separate clock link is far better still
One side effect of this is that the cable dress (bends cause extra loss) will have an effect on the jitter.
If you are actually getting bit errors on a fibre optic link something is very wrong.
Coax links are much better, and using a separate clock link is far better still
It is not hard to build a good coax SPDIF TX/RX circuit. Even a lousy one should out-perform TOSLINK.
Getting rid of the jitter needs to be done after the RX chip. That is a bit trickier, but that holds true no matter how you get the signal from the transport to the DAC.
Others have accurately stated the problems with TOSLINK, no need for me to repeat them. There is simply no reason to use it. Period.
Ok..........if your circuit radiates too much, and you simply can not tolerate any EMI..............
(There are ways to fix that.)
Jocko
Getting rid of the jitter needs to be done after the RX chip. That is a bit trickier, but that holds true no matter how you get the signal from the transport to the DAC.
Others have accurately stated the problems with TOSLINK, no need for me to repeat them. There is simply no reason to use it. Period.
Ok..........if your circuit radiates too much, and you simply can not tolerate any EMI..............
(There are ways to fix that.)
Jocko
Jocko Homo said:
Hi Jocko,
I know you have tons of experience here, could you point me to a link on how to build a "good coax SPDIF" receiver circuit ("really good" preferred!). Lets just say that getting rid of the jitter after the RX chip is not an option, so may as well reduce the jitter as much as possible at the RX right?
Cheers!!
Clem
Well........
Since I keep everything in my head......and I never write anything down.......I'm not sure exactly where "my students" have posted what they have managed to wrangle out of me. I'll look around......maybe I will find something. Sit tight, don't hold your breath. Maybe one of them will come forward, and save me the effort.
Jocko
Since I keep everything in my head......and I never write anything down.......I'm not sure exactly where "my students" have posted what they have managed to wrangle out of me. I'll look around......maybe I will find something. Sit tight, don't hold your breath. Maybe one of them will come forward, and save me the effort.
Jocko
OK........here is one place to look.......
It is only part of the circuit. I think everyone is waiting on me to give them the rest of the clues. Lots of other good stuff in that thread.
http://www.diyhifi.org/forums/viewtopic.php?p=5761#5761
Jocko
It is only part of the circuit. I think everyone is waiting on me to give them the rest of the clues. Lots of other good stuff in that thread.
http://www.diyhifi.org/forums/viewtopic.php?p=5761#5761
Jocko
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