Asrock B85M Pro4 DPC latency

[tuga4ever]

Hi,
I'm having audio pops every few minutes to an hour. When it pops it's only one pop.
I did a clean install of windows 8.1, installed all latest drivers but the problem presisted.

After i disable the CPU C-states i have no more audio pops or DPC latency spikes. I'm sure the problem is the BIOS (latest 1.90), anyone has similar problems? Will Asrock fix this?

I had DPC latency spike of 4000us once with C-states enabled, with c-states disabled i never saw DPC get over 400us in 30 minutes under normal use and streamming music through spotify.

Edit:
i5 4570
asrock b85m pro4
gskill 2x4gb 1600 cl9
gtx 660ti
xfx 550w

[parsec]

Re: Asrock B85M Pro4 DPC latency

High DPC latency is common on Intel 8-series chipset boards, although that varies a bit between manufactures. In general it is higher than previous Intel platforms.

Don't forget what C-states do, they are a CPU power saving feature. The "higher" (or lower, depending on your perspective) the C-state (C1 to C6, and C7 in Haswell processors) the more a processor core is reduced from its normal operating state. As a core is in a higher C-state, the longer it takes to come out of it to the core's normal operating state. Although that time is short, it can be noticeable, as you have seen when you disabled C-states on your board.

The way that C-states work is how Intel designed it, and is not under the control of a board's BIOS, except to enable or disable them. So it is impossible for a board manufacture to fix anything in a BIOS (which they purchase from someone else, AMI for ASRock boards) related to C-states.

Are the pops you get on your PC are more like a noise, or a momentary mute followed by the audio continuing? The former could be a static electricity discharge, but since that does not happen with C-states disabled, it probably isn't a static discharge.

Your testing of the DPC latency with C-states on and off IMO confirms it is the high C-states causing the problem.

What other specific BIOS problem could be fixed, as you think is possible?

[tuga4ever]

Re: Asrock B85M Pro4 DPC latency

The pops are a momentary mute followed by the audio continuing, i noticed now they still happen with C-states off.

I will do some more testing, since i only can hear them with my headphones on, the pops have low volume. I'm using Xonar DG as a sound card.

[parsec]

Re: Asrock B85M Pro4 DPC latency

One thing you can try is an option in your Windows Power Plan. In the Advanced settings, the PCI Express entry has the Link State Power Management option. If it is set to Maximum or Moderate power savings, try setting it to Off.

The pops on the headphones could be a momentary loss of connection caused by the headphone jack on the PC, or the plug on the headphones.

[tuga4ever]

Re: Asrock B85M Pro4 DPC latency

My sound card is PCI.

When the pop happens the audio is not interrupted.

I'll have to test this better since my sound card is right under my graphics card and it can electrical interference.

Edit: I think i've found the issue, i had the pci bracket from the sound card in contact with the graphics card's bracket, i had to unscrew the sound card and screw it again about 2 millimiters below. I haven's heard any pops since. I'll watch a movie to see if it pops again, it used to pop more often when i was playing games or watching movies.

I've disabled C3 power state since it makes almost no difference in power consumption and reduces DPC spikes a lot. I've also disabled C6 and C7 since my PSU doesn't support it.

[tuga4ever]

Re: Asrock B85M Pro4 DPC latency

It's fixed, audio pops are gone.

[parsec]

Re: Asrock B85M Pro4 DPC latency

Great, and interesting fix. Could have been a grounding issue, when the cards were in contact with each other via the brackets. Or static was discharging from the video card into the sound card. Thanks for the info, I'll remember this.