HDMI vs. Coaxial Digital Interconnects

[garylkoh]

Thanks for that Gary! Geez, I have Neutrik XLR, TRS, and Speakon connectors all over various installs, never considered their RCA line... Duh!

Glad to be of help. I'm going to be building a S/PDIF cable using these using Amir's and your guidance in this and the other threads and hopefully get to even more transparency for my analog/digital dialectic.

[Orb]

I borrowed a 1 meter and a 2 meter UltraLink coaxial cable (Challenger II), both low/mid priced from the same line. I also borrowed a 2 meter Purist Audio 75 Ohm cable (retail ~ $330) to compare.

Results: The 1 meter exhibited the midbass tubbiness and lack of high-frequency extension I mentioned with my own coaxial cable. The 2 meter reduced that tubbiness a bit, but still lacked the high end extension. The Purist Audio cleaned up the midbass a bit more, but still left some tubbiness. It had a bit more extension, but still not the transparency of the Purist HDMI in my system.

It is quite possible that the coaxial output of my Denon 3930CI has an intrinsically high level of jitter, which no coaxial cable can rectify. In the end, I still preferred the HDMI from my Denon 3800 Blu-ray player for CD playback.

Lesson learned: Each device probably has unique levels of jitter and also differing levels of attention paid to different circuits in that device. A little experimentation is probably necessary in any case to achieve the best results.

Lee

More for Don/Amir.
Is this possibly down to slight impedance mismatch causing reflections (whether connector or chip-hardware)?
Reason I ask is that I never see this myself when using AES-XLR digital connections (use 1m most of the time but had longer in comparison).

This aside, one thing this raises that I feel is of interest is how some products can support 192/24 over their single RCA S/PDIF while many do not try to implement this, seems to be a combination of all that is so far discussed including quality of the S/PDIF receiver chip/etc.

Thanks
Orb

[naturephoto1]

I borrowed a 1 meter and a 2 meter UltraLink coaxial cable (Challenger II), both low/mid priced from the same line. I also borrowed a 2 meter Purist Audio 75 Ohm cable (retail ~ $330) to compare.

Results: The 1 meter exhibited the midbass tubbiness and lack of high-frequency extension I mentioned with my own coaxial cable. The 2 meter reduced that tubbiness a bit, but still lacked the high end extension. The Purist Audio cleaned up the midbass a bit more, but still left some tubbiness. It had a bit more extension, but still not the transparency of the Purist HDMI in my system.

It is quite possible that the coaxial output of my Denon 3930CI has an intrinsically high level of jitter, which no coaxial cable can rectify. In the end, I still preferred the HDMI from my Denon 3800 Blu-ray player for CD playback.

Lesson learned: Each device probably has unique levels of jitter and also differing levels of attention paid to different circuits in that device. A little experimentation is probably necessary in any case to achieve the best results.

Lee

Hi Lee,

Thanks for the update. However, I am still of the opinion that cables need a burn in process including Coax and probably even HDMI. But, you have demonstrated to yourself and it confirms my/our findings that different Coax cables sound different and in different lengths which is counter to what many claim. Did you have a chance to also compare different HDMI cables and in different lengths as well?

Rich

[RBFC]

Hi Lee,

Thanks for the update. However, I am still of the opinion that cables need a burn in process including Coax and probably even HDMI. But, you have demonstrated to yourself and it confirms my/our findings that different Coax cables sound different and in different lengths which is counter to what many claim. Did you have a chance to also compare different HDMI cables and in different lengths as well?

Rich

I didn't compare different HDMI cables. Since I use the HDMI-active player for Blu-ray anyway, I just went for the better cable and left it alone. Not as thorough, I know, but that's where it is currently. The reason I continued to try different coaxial cables is that I fully expected coax to be better than HDMI due to published data on jitter.

Lee

[Orb]

......(Amir -- are there extra bits for scrambling and error detection/correction in the S/PDIF format?).......

Because the datastream stucture is a frame format, its best to present this as an overhead; there is a minimum and maximum number of data bits transmitted in a subframe that will require preamble-control-sync-etc bits.

Going over one of the links I gave it comes out to this:
Every sample is transmitted as a 32-bit word (subframe). These bits are used as follows:

bits meaning
0-3 Preamble (see links; special structure)
4-7 Auxillary-audio-databits (used for 24 bit recordings however I think its invalid to use this as 24bit data for AES/EBU XLR)
8-27 Sample-Actual Audio Data (can set up to 20 bit recordings max)
A CD-player uses only 16 bits, so only bits 12 (LSB) to 27 (MSB) are used. Bits not used are set to 0).
To transmit 24bit recordings it must used the bits relating to 4-7.
28 Validity When this bit is set, the sample should not be used by the receiver. A CD-player uses the 'error-flag' to set this bit.
29 Subcode-data
30 Channel-status-information
31 Parity (bit 0-3 are not included)

So for every 32bits transmitted (this is data and other stuff as shown above), we have an overhead for audio between 8-to-16bits (depending if 16,20,24 bit recording).
This is repeated for each channel, so the above subframe example would be for 1 channel, then the next subframe will be the other stereochannel.

The preamble is the bits used to ensure the break is seen between each channel and can also hold the sync information.
That sync info is different to the DAC clocking, as the DAC clocking is embedded with the data (how this changes its looks is also shown in the links).

Ah where it was asked, the bitrate frequency is 2.8mhz when transmitting CD.
Cheers
Orb

Edited for corrections.