Jocko,
That is fine and clears things up for immensely. The fact that the master clock is embedded in the source signal tells me 2 things... avoid a crystal (new clock) and the potential for infinite data storage as there is no handshaking to interrupt data transmission.
Once again, we have been led down the "golden path" by schleps. that need to save 50 cents in wire or a buck or two in dual bus RAM.
I'll remember to stay away from spdif in the future. I have always been "****** off" about the cheap crystals put in CD players and the like. I don't have "perfect pitch" or at least never thought so... but listening to music "flat" or "sharp" bothers me a bit.
Thanks,
That is fine and clears things up for immensely. The fact that the master clock is embedded in the source signal tells me 2 things... avoid a crystal (new clock) and the potential for infinite data storage as there is no handshaking to interrupt data transmission.
Once again, we have been led down the "golden path" by schleps. that need to save 50 cents in wire or a buck or two in dual bus RAM.
I'll remember to stay away from spdif in the future. I have always been "****** off" about the cheap crystals put in CD players and the like. I don't have "perfect pitch" or at least never thought so... but listening to music "flat" or "sharp" bothers me a bit.
Thanks,
Since I do not know you.........
I have no idea where you were back in the early 80s.
I was reading the stinking JAES, and the only thing useful that I ever got out of it was seeing what a kludge CDs in general, and SPDIF in specific, were going to be.
J. A. Pan, Inc. wanted a 32 Khz sample rate. Tom Stockham pushed for 100 kHz. We were lucky they budged to 44.1 kHz.
SPDIF......and its evil twin....AES/EBU.......
Well, I don't think they ever expected anyone to use SPDIF. Besides, it was only consumer gear, and good enough is more than good enough. My proof: they introduced TOSLINK to do it. Yuk. The coax versions on Sony and Philips gear is awful, designed to minimise EMI.
AES/EBU was even more flawed. I talked to the guy who headed up that group (I think he did.........he is/was a big name in the "bidnis", and was at least one of the high mucky-mucks). I 'splained to him what was wrong.......he listened.........thanked me.......and several years later they revised it. Probably because they found out it did not work as planned. It is still lousy, but better than it was.
The crystals are not bad. Had one spec'ed by someone in that "bidnis": Q = 100 k. They would like to have sold me a primo one, Q = 150 k, for $$$$. Nope, the crystal is not the problem. It is that they usually stick the xtal in the filter chip. Yuk.
Speaking of "Crystal"........the info that they give in their data sheets runs counter to everything that I have learned in the.........14 or so years ......that I have futzing with it. The Schmitt trigger inputs have to go for starters.
Jocko
I have no idea where you were back in the early 80s.
I was reading the stinking JAES, and the only thing useful that I ever got out of it was seeing what a kludge CDs in general, and SPDIF in specific, were going to be.
J. A. Pan, Inc. wanted a 32 Khz sample rate. Tom Stockham pushed for 100 kHz. We were lucky they budged to 44.1 kHz.
SPDIF......and its evil twin....AES/EBU.......
Well, I don't think they ever expected anyone to use SPDIF. Besides, it was only consumer gear, and good enough is more than good enough. My proof: they introduced TOSLINK to do it. Yuk. The coax versions on Sony and Philips gear is awful, designed to minimise EMI.
AES/EBU was even more flawed. I talked to the guy who headed up that group (I think he did.........he is/was a big name in the "bidnis", and was at least one of the high mucky-mucks). I 'splained to him what was wrong.......he listened.........thanked me.......and several years later they revised it. Probably because they found out it did not work as planned. It is still lousy, but better than it was.
The crystals are not bad. Had one spec'ed by someone in that "bidnis": Q = 100 k. They would like to have sold me a primo one, Q = 150 k, for $$$$. Nope, the crystal is not the problem. It is that they usually stick the xtal in the filter chip. Yuk.
Speaking of "Crystal"........the info that they give in their data sheets runs counter to everything that I have learned in the.........14 or so years ......that I have futzing with it. The Schmitt trigger inputs have to go for starters.
Jocko
Re: Re: Re: Re: Digital stream switching
Well, time and time again I find that if I do A/B testing with friends, and there is no audible difference, they all blame the switches and/or the cabling for masking differences that HAD to be there. So, by keeping the switching absolutely simple, I try to circumvent that particular trap. Not sure it'll be enough though.
Jan Didden
rfbrw said:
Well, time and time again I find that if I do A/B testing with friends, and there is no audible difference, they all blame the switches and/or the cabling for masking differences that HAD to be there. So, by keeping the switching absolutely simple, I try to circumvent that particular trap. Not sure it'll be enough though.
Jan Didden
Jan Didden,
While I can't speak for Jocko, I pretty certain he was not referring to the effects of "Off Isolation" between inputs, and the resultant effect on jitter....
With only 30dB to 40dB isolation between inputs infers that the "Off" signal modulates the "On" signal by -30dB to -40dB which is pretty disastrous from a Jitter performance standpoint.
John
While I can't speak for Jocko, I pretty certain he was not referring to the effects of "Off Isolation" between inputs, and the resultant effect on jitter....
With only 30dB to 40dB isolation between inputs infers that the "Off" signal modulates the "On" signal by -30dB to -40dB which is pretty disastrous from a Jitter performance standpoint.
John
Re: Since I do not know you.........
Ideally, the master system clock should reside electrically near the DAC chip itself, the point where the digits become analog audio. Not in the digital only transport box and the DAC only having a PLL (which always have jitter no matter how skillfully designed). Or at least have a clock only coax cable in addition to the data coax cable (could have used "S video" cables for this, those are just a pair of 75 ohm coax cables, nothing more). You'd just take the master clock, buffer it, feed the coax, and receive it at the far end with a simple buffer (not a PLL) and feed that to the DAC. The data coax can have large amounts of jitter but it would get reclocked and cleaned up. In the digital domain, as long as the FIFOs are large enough, jitter isn't a big issue. The data coming off the disk itself likely has a large amount of "wow and flutter" but that is cleaned up with the use of a FIFO clocked off a stable clock (and the FIFO tells the disk spin motor to spped up or slow down to keep the FIFo about half full). In any event, it's at the DAC chip where the rubber meets the road.
Jocko Homo said:
Ideally, the master system clock should reside electrically near the DAC chip itself, the point where the digits become analog audio. Not in the digital only transport box and the DAC only having a PLL (which always have jitter no matter how skillfully designed). Or at least have a clock only coax cable in addition to the data coax cable (could have used "S video" cables for this, those are just a pair of 75 ohm coax cables, nothing more). You'd just take the master clock, buffer it, feed the coax, and receive it at the far end with a simple buffer (not a PLL) and feed that to the DAC. The data coax can have large amounts of jitter but it would get reclocked and cleaned up. In the digital domain, as long as the FIFOs are large enough, jitter isn't a big issue. The data coming off the disk itself likely has a large amount of "wow and flutter" but that is cleaned up with the use of a FIFO clocked off a stable clock (and the FIFO tells the disk spin motor to spped up or slow down to keep the FIFo about half full). In any event, it's at the DAC chip where the rubber meets the road.
janneman said:
I was referring to the relatively complex nature of glitch-free switcher compared to a simple switch. A glitch-free switcher switches at the start of an audio frame, so a far as the dac is concerned there is no discontinuity therefore no noise on swithing inputs. For this to work, all the inputs have to be synchronized which means each input has to have its own SPDIF decoder and the whole system has to run off a common clock. In a facility or a studio this is common practice. At home things are a little different but then again with some of the people around here I'm not so sure.
rfbrw said:
OK, I read you. In my app this wouldn't be a problem; it's OK for the listeners to hear that there is a switch over. But all the previous posts now make me think the RF switch idea probably isn't a good one. But the alternative of using an solid state switch or more complex buffering-and-distribution would defeat the purpose of comparing two digital sources unprocessed as much as possible.
So what do I do now?
Jan Didden
Maybe not.
Look here https://www.surplussales.com/Relays/rfcoaxialrelays/rfcoax_bnc.html
for cx-230 (56dB isolation).
The isolation will be improved by using two relays (picture below).
Regards,
Milan
Attachments
Jan,
Just out of curiosity, what are looking to learn/dispell with your A vs. B testing?
I ask because based on Jocko's explanation, the ones and zeros may be the same, but their time-of-arrival would indeed have the potential to cause distortion. The signals are undoubtedly derived from crystals... so the accuracy, as long as the signals are kept clean, is probably more than sufficient.
Either way, I am on your "side".
Just out of curiosity, what are looking to learn/dispell with your A vs. B testing?
I ask because based on Jocko's explanation, the ones and zeros may be the same, but their time-of-arrival would indeed have the potential to cause distortion. The signals are undoubtedly derived from crystals... so the accuracy, as long as the signals are kept clean, is probably more than sufficient.
Either way, I am on your "side".
Here.........build something like this for each input:
http://www.diyhifi.org/forums/viewtopic.php?p=5761#5761
You can then use relays after to switch inputs. It will have the benefit of making it sound better than using the stock '841x all by itself.
Don't know about the paper you are refering to, as I left the AES by then. But if you recall, the original incarnation allowed for......what was it...........3 transmitters and 7 receivers, all hung on the same coax.
Yeah, I know.....Ethernet did similar stuff. The diference was it didn't have to sound good.
Jocko
http://www.diyhifi.org/forums/viewtopic.php?p=5761#5761
You can then use relays after to switch inputs. It will have the benefit of making it sound better than using the stock '841x all by itself.
Don't know about the paper you are refering to, as I left the AES by then. But if you recall, the original incarnation allowed for......what was it...........3 transmitters and 7 receivers, all hung on the same coax.
Yeah, I know.....Ethernet did similar stuff. The diference was it didn't have to sound good.
Jocko
poobah said:Jan,
Just out of curiosity, what are looking to learn/dispell with your A vs. B testing?
I ask because based on Jocko's explanation, the ones and zeros may be the same, but their time-of-arrival would indeed have the potential to cause distortion. The signals are undoubtedly derived from crystals... so the accuracy, as long as the signals are kept clean, is probably more than sufficient.
Either way, I am on your "side".
Well, after several years on this forum I am slowly getting converted to the value of a comparative listening test (as long as it is blind, of course
. This particular test should tell me whether all CD drives sound the same or not. I mean we know that bits is bits, but there is the issue of jitter (time distortion?). So by transparantly switching between CD drive digital outputs either there will be an audible difference or not. If there is, it's good to know because we can improve the sound by improving the CD drives/ digital output. If there isn't, there is another question: is it because all CD drives sound the same or is it because the rest of the system masks the differences?Either way, it should prove interesting.
Jan Didden
Pardon the digression, but.......
Many years ago, when my company was making money, I needed trained listeners to evaluate the products we were developing.
The first step in chosing a tester was to put a short cable in the tape loop, and see if they heard a difference. Add to that, sometimes I would flip the switch, but they were still listening to the same position, over and over.
The guys who claimed they heard a BIG difference flunked. I won't mention any names, as you guys may recall one or two of them as members here. Heh, heh.
Now I know.......some will claim that there should have been at least SOME difference. OK........FWIIW......Dave Wilson.......you know who he is........he will claim that he can hear differences in wire, solder, etc, blah, blah.
He probably can. But he uses several dozen or so tied together, not just one by itself. That is how he does it.
Jocko
Many years ago, when my company was making money, I needed trained listeners to evaluate the products we were developing.
The first step in chosing a tester was to put a short cable in the tape loop, and see if they heard a difference. Add to that, sometimes I would flip the switch, but they were still listening to the same position, over and over.
The guys who claimed they heard a BIG difference flunked. I won't mention any names, as you guys may recall one or two of them as members here. Heh, heh.
Now I know.......some will claim that there should have been at least SOME difference. OK........FWIIW......Dave Wilson.......you know who he is........he will claim that he can hear differences in wire, solder, etc, blah, blah.
He probably can. But he uses several dozen or so tied together, not just one by itself. That is how he does it.
Jocko
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