Will a bridged PCI slot pollute digital audio in my case?

[chane]

WOW, is it true that PCI implementation is so poorly executed in Z97 boards, at least in part, due to “bridged” or “shared” data or system resources between PCI and PCIe slots? If so, then I presume that this board http://www.asus.com/us/Motherboards/Z97MPLUS/ has a “bridged” PCI slot like this one does
http://www.hardocp.com/article/2014/08/21/asus_z97a_lga_1150_motherboard_review#.VBCf-aNuVYU
Does that mean that rather than a separate hard-wired connection, some kind of chip is used between the PCI and PCI-e slots to share data and resources between them?

That’s why I was advised at Gear Slutz to choose a CPU using a board with a 2011 socket instead,which unlike 1150 boards do not have bridged PCI slots.

Actually, since my last post, I’ve switched from choosing to build an all-in-one ATX desktop (for 1080p video encoding plus HD audio editing and serving) to an audio only micro-ATX.What audiophile could forget the cardinal rule that “separates” are always better? Since audio signal quality is top priority, I’d choose a 2011 socket low power CPU equivalent to one like the Haswell 4790T or 4785T (45 and 35 w TPD). Going this route might insure that my audio won’t get contaminated with higher amplitude RF and/or EMI radiation from a more powerful CPU, video card GPU or the bigger power supply to run them. And since I’ll being playing no games or movies on this pc, only a lean, low power (nVidia) video card would be needed. A Samsung 840 EVO SSD for the system drive and a CD ROM drive for CD ripping completes it.

However, looking for boards with the 2011 socket at the ASUS site, I found next to no ATX boards and only one micro-ATX board, and that one has no PCI slot.

BUT wait! If I did choose a micro-ATX board with an 1150 socket, since I’m doing zero video intensive stuff on this dedicated audio pc, I wouldn’t need a video card if I use the Haswell CPU’s on-chip graphics. So with no (PCIe) video card, my M-Audio PCI card won’t have to “compete” with any PCIe card’s data and no related latency or noise issues should arise. Yes?

On the other hand, it’s quite possible that I will eventually want to add just one PCIe card: A USB card to feed my external DAC. Like this one http://jplay.eu/jcat/ -and powered by an external linear supply. If both my M-Audio card’s SPDIF output and this card’s USB port were outputting data simultaneously that just might cause a sonic mess. BUT unlike a PCIe video card-which would be constantly on line-I’d only be outputting data to my DAC from one of these two digital sources at a time. Moreover, since the USB card is externally powered, I could cut it out of circuit by simply shutting off its external power supply, while outputting from the M-Audio card’s SPDIF (In fact, if the ASUS Z97-M Plus is much like the Z97-A board, its software interface may allow for powering off the M-Audio card too But don’t quote me on that one).

But is THAT why ASUS Tech Support said that though the Z97-M Plus board has a standard sized PCI slot to accept my M-Audio card, the card must be able to work in “X-4” mode? Did he mean that when sharing data path lanes (?) with the video card it would need to have 4 times the throughput as
an ancient PCI 1X card?

However, it says on the M-Audio card’s box “Delta cards have been re-designed to be PCI 2.2 compliant, with support for 3.3v and 5v PCI signaling environments. This guarantees compatibility with PCI-X, 64-bitand standard 32-bit based systems, including Apple G5”.

How does PCI 2.2 relate to “X4” mode?

In any case, again, I can externally power off that USB card,
that would then give the M-Audio card full data lane access (?).

Therefore, would this scheme obviate the need to go with a
2011 socket motherboard to gain an unbridged PCI slot for best performance from my PCI soundcard’s SPDIF output?

 

[heymrdj]

PCI 2.2 doesn't relate to X4 at all. X4 is the amount of lanes it needs on the PCIe system. PCI2.2 is a standard of the old pci slots.

Haswell doesn't really do PCI, at least the PCH's attached to them don't. The PCI slot communicates with the processor through a PCIe converter.

Intel® 8 Series / C220 Series Chipset Family Platform Controller Hub (PCH)
Datasheet
June 2013
...
5.2.1 PCI Bus Interface
The PCI Bus Interface is not available on any PCH SKU.

5.2.2 PCI Legacy Mode
PCI functionality is not supported on new generation of PCH requiring methods such as
using PCIe*-to-PCI bridges to enable external PCI I/O devices. To be able to use PCIe-to-
PCI bridges and attached legacy PCI devices, the PCH provides PCI Legacy Mode.
PCI Legacy Mode allows both the PCI Express* root port and PCIe-to-PCI bridge look
like subtractive PCI-to-PCI bridges. This allows the PCI Express root port to
subtractively decode and forward legacy cycles to the bridge, and the PCIe-to-PCI
bridge continues forwarding legacy cycles to downstream PCI devices.

Note: Software must ensure that only one PCH device is enabled for Subtractive decode at a
time.

 

[chane]

PCI 2.2 doesn't relate to X4 at all. X4 is the amount of lanes it needs on the PCIe system. PCI2.2 is a standard of the old pci slots.

Haswell doesn't really do PCI, at least the PCH's attached to them don't. The PCI slot communicates with the processor through a PCIe converter.

So I guess this means that a micro-ATX board with a 2011 socket is the only good way to go for error and noise free digital audio from a PCI sound card's SPDIF output. Yes?

If so, can you recommend the latest family of Intel CPUs that would be best to use-with TPDs in the 35 to 65w range?

AND will those CPUs work without a "bridge" when communicating with the PCI sound card?

 

[heymrdj]

No I don't really agree with the audiophiles view of pci lanes so I don't really have a recommendation. All I can say is if its a big ordeal get a newer version of the card with native pcie. There is no modern system I would recommend for the money that doesn't emulate pci over pcie.

 

[chane]

All I can say is if its a big ordeal get a newer version of the card with native pcie. There is no modern system I would recommend for the money that doesn't emulate pci over pcie.

The ONLY reason I even bought this M-Audio card is because it alone contains the drivers to run Pro Tools 7.4 DAW software-that I spent $250. on and hundreds more for Serato's Pitch n Time Pro plugin. Then, more than 6 years later, Avid
now makes Pro Tools 10 with software drivers, allowing the user his own choice of hardware. But that upgrade is over $300. Insanity for audiophiles who only edit and play stereo wav files of CD track rips. But I love Serato PnT-probably the best sounding plug in of its kind. Unfortunately, it runs only on Pro Tools. So I need a pc to run that M-Audio PCI card with no hang ups. And no, M-Audio, nor the company that recently bought it, makes a PCIe version.

But if it's true that motherboards having the 2011 sockets use no bridge between the PCI and PCIe slots, then doesn't the mating CPU and/or the PCH communicate directly with the PCI card? Or would I actually have to go back to this hardware
this ancient to do that?
http://en.wikipedia.org/wiki/Southbridge_(computing)

 

[heymrdj]

For the most part other than some niche builds Intel dropped support back after the Q67 chipset for the first i series processors. So a system newer than mid 2011 most likely will not have it. Again, I wouldn't build with anything that old. You can get more time with the C200 chipset, for xeons. With boards based on the E3 Xeon (earlier, not the newest ones) and C200 chipsets you get native PCI. But they're dropping it now too, so again you'll need to use 1-2 year old hardware to make it work.

 

[chane]

I read here www.intel.com/content/dam/.../6-chipset-c200-chipset-datasheet.pdf on p. 123 about how when the user places the chipset in Legacy Mode that the PCIe bridge will look as a “subtraction” to the PCI card-as if PCIe were gone from the routing
of the PCI card’s data and clocking signals?

But would this all likely result in any clearly discernable improvement in two channel stereo digital audio transmission quality from the PCI card’s SPDIF output connector to my external audio DAC? That is, would the digital audio quality likely be substantially better-less chance for noise, data corruption, jitter, latency issues, etc-than if the PCI card
were used in this Haswell Z97 chipset
http://www.asus.com/us/Motherboards/Z97MPLUS/

If the answer is yes, please describe the improvement(s).

And again if yes, please suggest some of those older E3 processors listed here

http://en.wikipedia.org/wiki/Intel_Xeon_chipsets and the C200 and/or here

http://en.wikipedia.org/wiki/List_of_Intel_Xeon_microprocessors

If possible, please choose the CPU(s) for best PCI support that are available in low power versions. This is an audio only pc (no gaming or video encoding), so CPUs as low as 35 watts, 70 w max TPD is fine. That would be great because I’m also hoping to find the C200
chipset in a micro-ATX size.

 

[heymrdj]

I wouldn't know. I'm not nearly into hardware that much. You asked for something that runs native pci, which I provided. I still understand nothing of how all this actually helps the industry. In my field if something requires control so that the possible 1/100th of a second of lag introduced by a hardware abstraction layer is an issue, we get specially build systems with RTOS. We dont bother with hacking together whiteboxes to do the job. But I also run a simple FiiO amp and some cans. Im not a major audio guy and find no discernable difference worth the $$$ above this 400$ of equipment.

 

[richaron]

Not really answering questions, just dribbling ideas. My (Gigabyte) motherboard has dedicated "DAC-UP" USB port designed to have clean power (like that PCIe card you listed). I've seen some high end recent ASUS boards with a similar idea.

I have no idea what's going on in motherboards if they somehow let PCIe devices influence the PCI bus (and I would be interested to know). Obviously this is not ideal. But if you were looking for "audiophile" I don't think you would be using an old, unshielded, PCI internal sound card as your DAC anyway (are you?).

Plus I doubt any possible PCI problems will make a difference in audio quality:
-you will probably never need low latency.
-you will probably never need full PCI bandwidth.
-all audio devices have power circuitry of their own.

Therefore, would this scheme obviate the need to go with a 2011 socket motherboard to gain an unbridged PCI slot for best performance from my PCI soundcard’s SPDIF output?

SPDIF is digital... Any SPDIF device, ever made, at any price, will make exactly the same signal.