MJL21193 said:
Connect a mile of Cat5 between your transport and DAC and tell us what happened. 😉
What we need is a Meitner for the digital questions on this thread, rather than me (mostly analog) or the hear no difference and proud of it, fraternity.
I have designed a CD reproduce system(didn't go into production) and have been around digital audio for 40 years, but I still don't think much of digital that I can actually afford.
I have designed a CD reproduce system(didn't go into production) and have been around digital audio for 40 years, but I still don't think much of digital that I can actually afford.
john curl said:
Good question … 🙂
RCA connectors should be 75 Ohm. Sometimes this is their actual impedance, sometimes not …
One more reason for careful selection of parts …
dac's don't have crc or packet inspection ..BTW cat 5 can only go
about 300' before loss occurs.. they need repeaters or hubs
to go the distance.. optics are the way to go.. look at the telco's.
OS
Andre Visser said:
Instead of doing that...
How about I buy a box or two, cut it into 1 metre lengths, slip some sleek braided sheathing around it, fit a pair of cheap RCA'a on the ends and sell them to folks like you for $500 a pop. 100 metre per box --- $50,000.
Joshua_G said:
????
Joshua_G said:
It is physically impossible for an "RCA" connector to be 75 Ohms. Not even 50 Ohms. If to take the ratio of OD of the pin and ID of the connector ring its below 50 Ohms with just air. Add a female connector and its a lost cause. Same for a PAL connector (Used in EU for RF connections on 75 Ohm cables). A proper 75 Ohm connector is special- either a 75 Ohm BNC (no plastic ring around the center female contact) or a 75 Ohm N connector. Everything else you will encounter will reflect some energy, and those reflections will cause jitter in the signal. How effective the receiver PLL is at rejecting them is the real issue. And reclocking, buffering etc. all help. But they only reduce it, not eliminate it.
Comparing digital audio (or video) to data transmission is misleading. Data over a link like Ethernet, or over the internet isn't too time sensitive. A few milliseconds late is invisible on a document. However a few milliseconds is a loud pop on audio and a badly garbled picture on video.
S/PDIF is from a family of self clocking data links. They do work quite well if your tolerance for timing errors is pretty wide. The data in HDMI is passed the same way, but its timing tolerance is much higher- approx 30% jitter of the bit rate will get the bits decoded properly and it will end up lighting the correct pixel on the LCD (how can it miss?). However the importance of jitter in audio was not understood when S/PDIF was designed. Early CD players only used 14 of the 16 bits, and shared the DAC between channels. Getting better was not essential to launching the product. However when we talk about audio now the DACs are expected to be accurate to at least 1/2 LSB. That means the timing of the clock must be better still to meet a minimum accuracy, or better than 1 part in 2 to the 17th of the sample rate. (or less than 100 dB down). It really needs to be much better.
To put this problem in perspective-A crude analogy is trying to know the precise second when all you have as a reference is when the sun is exactly overhead. At that instant you are pretty close if you can detect it precisely, but your next chance to synchronize is 24 hours later. It requires a lot of precision to be stable, and a long time to get it right. If the seconds weren't critical, no problem, if they are critical its a big challenge.
I'm glossing over a lot with this, it gets quite involved, but I hope I have made the overall issue a little clearer.
MJL21193 said:Instead of doing that...
How about I buy a box or two, cut it into 1 metre lengths, slip some sleek braided sheathing around it, fit a pair of cheap RCA'a on the ends and sell them to folks like you for $500 a pop. 100 metre per box --- $50,000.
????
Yes, why don't you try it? If your theory is correct you can make lots of money.
I would not be interested though, I hope you will have a use for them afterwards. 😉
WBT have a new (well, almost) range of RCA connectors and sockets that they claim have 75 Ohms impedance and bandwidth up to 1 GHz, and they are obviously not full metal constructions. What is your take on those?
FIFO
The first time I was using a FIFO was 38 years ago (a chip from Western Digital). 😀
Regards,
Edmond.
john curl said:
The first time I was using a FIFO was 38 years ago (a chip from Western Digital). 😀
Regards,
Edmond.
MJL21193 said:
Wrong again.
Firstly I would compare it first with a known good digital interconnect and even if it is better, I would not buy it because I've mentioned earlier that I dont like the format, therefore I don't use it. 😉
MRupp said:
There are "workarounds" or compromised that may help a little. if the discontinuity is short with respect to the wavelength of interest it should not cause a reflection. But we don't know how sensitive or what the real minimum wavelength of interest is. If the "target of 10 pS jitter is indicative of the minimum wavelength you can't take any chances. Or you can leave out some of the metal, but you need to do both ends and then you lose the coaxial shield which causes impedance mismatches and emi problems.
Most of the "75 Ohm" RCA's I have seen's real claim was a coaxial crimp shield like a BNC but the connector has the same dimensions as every other RCA.
These are easy to see with a fast TDR. They also effect video, where they are visible as ghosts. Every 75 Ohm RCA I have looked at has been below 50 Ohms.
1audio said:
In the days that I've bothered with surround sound I've used Ecosse The Director SE, now for the next war, it needed to be played in for at least a week before it performed well, when new it was about the same as my homemade '75 Ohm' cable.
Andre Visser said:
A quality name. Easier to effectively market something if it can be personified. I shall call mine "El Gato (5e)" 😀
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