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#1
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toslink vs digital cable
Why is the digital coax more accurate than toslink? I thought that light
transmission had a wider bandwidth? |
#2
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Nitro M884 wrote:
Why is the digital coax more accurate than toslink? I thought that light transmission had a wider bandwidth? Digital coax is not necessarily more accurate than Toslink. The bandwidth difference is irrelevant, because the same amount of information (i.e., data) is being sent via the two media. Toslink cables have more loss per unit length compared to coax, and they are less suitable for long runs, unless you use very thick fiber cables. |
#3
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Nitro M884 wrote:
Why is the digital coax more accurate than toslink? I thought that light transmission had a wider bandwidth? "More accurate" is a matter of opinion. The optical-slaters will tell you that the jitter and other timing factors in an optical link is worse, along with less well-controlled rise and fall times. As far as data goes, all of the data gets transferred across an optical link just fine: individual bit failures would give barely noticeable clicks on PCM data, but would murder Dolby Digital and dts signals. I don't see why a properly engineered receiver couldn't make up for any minor timing errors in the signal with a small buffer. After all, PCM is clocked, so timing drifts or anomalies should be correctable. Don't forget to use a gold-plated optical cable, though! ;-) -- Mark. http://tranchant.plus.com/ |
#4
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Nitro M884 wrote:
Why is the digital coax more accurate than toslink? I thought that light transmission had a wider bandwidth? It's not. The quality of the transmission depends more on the specific receiver and transmitter than the type of cable. We've seen and measured cases where Toslink is better and others where coaxial is better. -- Len Moskowitz PDAudio, Binaural Mics, Cables, DPA, M-Audio Core Sound http://www.stealthmicrophones.com Teaneck, New Jersey USA http://www.core-sound.com Tel: 201-801-0812, FAX: 201-801-0912 |
#5
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Nitro M884 wrote:
Why is the digital coax more accurate than toslink? I thought that light transmission had a wider bandwidth? This is not true. A coax cable is driven by a pulse transformer, the bandwidth is at least a couple of 100MHz, almost only depending on the driver circuit. In an optical transmission we need a LED to change the signal into light and a receiver like a photodiode to change it back into an electric signal. The achievable data rate is only 6MHz, the bandwidth will be in the 10s MHz region, less than 10% of the coax. Nevertheless there will be identical performance, if you do not exeed the guaranteed data rate. -- ciao Ban Bordighera, Italy |
#6
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On 15 Dec 2004 00:51:29 GMT, Chung wrote:
Nitro M884 wrote: Why is the digital coax more accurate than toslink? I thought that light transmission had a wider bandwidth? Digital coax is not necessarily more accurate than Toslink. The bandwidth difference is irrelevant, because the same amount of information (i.e., data) is being sent via the two media. Toslink cables have more loss per unit length compared to coax, and they are less suitable for long runs, unless you use very thick fiber cables. One advantage of Toslink is that the optical cables avoid the possibility of ground loops. -alan -- Alan Hoyle - - http://www.alanhoyle.com/ "I don't want the world, I just want your half." -TMBG Get Horizontal, Play Ultimate. |
#7
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"Mark Tranchant" wrote in message
... Nitro M884 wrote: Why is the digital coax more accurate than toslink? I thought that light transmission had a wider bandwidth? "More accurate" is a matter of opinion. The optical-slaters will tell you that the jitter and other timing factors in an optical link is worse, along with less well-controlled rise and fall times. As far as data goes, all of the data gets transferred across an optical link just fine: individual bit failures would give barely noticeable clicks on PCM data, but would murder Dolby Digital and dts signals. I don't see why a properly engineered receiver couldn't make up for any minor timing errors in the signal with a small buffer. After all, PCM is clocked, so timing drifts or anomalies should be correctable. Don't forget to use a gold-plated optical cable, though! ;-) All of this begs the _real_ question. Why was TOSlink introduced to the audio world in the first place? There was never a crying need for it, and it's much more expensive. The only genuine advantage of optical interconnects is galvanic isolation, and my guess is that that is rarely important. Norm Strong |
#8
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"Ban" wrote in :
Nitro M884 wrote: Why is the digital coax more accurate than toslink? I thought that light transmission had a wider bandwidth? This is not true. A coax cable is driven by a pulse transformer, the bandwidth is at least a couple of 100MHz, almost only depending on the driver circuit. In an optical transmission we need a LED to change the signal into light and a receiver like a photodiode to change it back into an electric signal. The achievable data rate is only 6MHz, the bandwidth will be in the 10s MHz region, less than 10% of the coax. Nevertheless there will be identical performance, if you do not exeed the guaranteed data rate. Looks like toslink was designed with extremely limited expectations if what you're saying is correct. The networking guys have been sending gigabits over fiber for some time now. -- JS |
#9
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normanstrong wrote:
All of this begs the _real_ question. Why was TOSlink introduced to the audio world in the first place? There was never a crying need for it, and it's much more expensive. Is it? I thought the reason that a lot of lower-end equipment is optical only is that the co-ax interface requires the use of a (relatively) large, heavy and expensive wideband pulse transformer. -- Mark. http://tranchant.plus.com/ |
#10
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Jim wrote:
"Ban" wrote in : Nitro M884 wrote: Why is the digital coax more accurate than toslink? I thought that light transmission had a wider bandwidth? This is not true. A coax cable is driven by a pulse transformer, the bandwidth is at least a couple of 100MHz, almost only depending on the driver circuit. In an optical transmission we need a LED to change the signal into light and a receiver like a photodiode to change it back into an electric signal. The achievable data rate is only 6MHz, the bandwidth will be in the 10s MHz region, less than 10% of the coax. Nevertheless there will be identical performance, if you do not exeed the guaranteed data rate. Looks like toslink was designed with extremely limited expectations if what you're saying is correct. The networking guys have been sending gigabits over fiber for some time now. -- JS Toslink uses cheap fiber and cheap LEDs whereas networking gear uses high quality expensive fiber and lasers. Mike |
#11
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normanstrong wrote:
All of this begs the _real_ question. Why was TOSlink introduced to the audio world in the first place? There was never a crying need for it, and it's much more expensive. ... The cables and connectors are really dirt cheap to manufactu they're all plastic and no soldering is required for assembly And fiber is EMI-proof. -- Len Moskowitz PDAudio, Binaural Mics, Cables, DPA, M-Audio Core Sound http://www.stealthmicrophones.com Teaneck, New Jersey USA http://www.core-sound.com Tel: 201-801-0812, FAX: 201-801-0912 |
#12
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Nitro M884 wrote:
Why is the digital coax more accurate than toslink? I thought that light transmission had a wider bandwidth? What do you mean by accurate ? The early Toslink devices had a bandwidth of about 6-8 MHz. Coax easily beats this. Graham |
#13
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Jim wrote:
"Ban" wrote in : Nitro M884 wrote: Why is the digital coax more accurate than toslink? I thought that light transmission had a wider bandwidth? This is not true. A coax cable is driven by a pulse transformer, the bandwidth is at least a couple of 100MHz, almost only depending on the driver circuit. In an optical transmission we need a LED to change the signal into light and a receiver like a photodiode to change it back into an electric signal. The achievable data rate is only 6MHz, the bandwidth will be in the 10s MHz region, less than 10% of the coax. Nevertheless there will be identical performance, if you do not exeed the guaranteed data rate. Looks like toslink was designed with extremely limited expectations if what you're saying is correct. The networking guys have been sending gigabits over fiber for some time now. More recent Toslink devices are considerably faster IIRC. Don't forget it was designed as a cheap consumer part ! Graham |
#14
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Pooh Bear wrote:
Jim wrote: "Ban" wrote in : Nitro M884 wrote: Why is the digital coax more accurate than toslink? I thought that light transmission had a wider bandwidth? This is not true. A coax cable is driven by a pulse transformer, the bandwidth is at least a couple of 100MHz, almost only depending on the driver circuit. In an optical transmission we need a LED to change the signal into light and a receiver like a photodiode to change it back into an electric signal. The achievable data rate is only 6MHz, the bandwidth will be in the 10s MHz region, less than 10% of the coax. Nevertheless there will be identical performance, if you do not exeed the guaranteed data rate. Looks like toslink was designed with extremely limited expectations if what you're saying is correct. The networking guys have been sending gigabits over fiber for some time now. More recent Toslink devices are considerably faster IIRC. Don't forget it was designed as a cheap consumer part ! Graham Well, the TOTX173 has 6MHz data rate, and the fastest new link TOTX141 has 15MHz. But what matters is the jitter spec, which is for both +/-20ns. It also doesn't make sense to have a higher Data rate as the medium DVD cannot deliver even this rate(15MHz). In both cases the maximum cable length is 10 meters. Actually the data recovery circuit will digitally reduce the output jitter to values below 1ns, the external Benchmark DAC is a good example what is possible. -- ciao Ban Bordighera, Italy |
#15
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Correct me if I am wrong...
The digital signal from the source drives both the coaxial and the TOSlink output. Any jitter should therefore be the same on both outputs, since the conversion to optical happens after the signal is timed. I like the coaxial better, cables are cheaper and longer runs are possible. "Nitro M884" wrote in message ... Why is the digital coax more accurate than toslink? I thought that light transmission had a wider bandwidth? |
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