DPC latency = help urgently needed, *please!*

Hello

I've come here because I'm desperately in need of some technical help and I'm hoping that maybe somebody here can assist me before it's too late!

I'm a music producer and one half of a dance music act called Far Too Loud ( www.myspace.com/fartooloud). Having been DJing club gigs for some time, we're about to take our Live show on the road. For this purpose I have purchased a laptop with the following specs:

Dell Precision M6300
Intel Core2Duo X7900
4GB RAM
NVidia Quattro 1600M gfx
Windows XP Pro

Now this machine had been recommended to me by a few people, and I thought the fact that it was nice and powerful and a "workstation" machine would mean that it would be nice and stable for live use...however I was wrong.

It seems that I'm unable to run my audio at low latency without it suffering from dropouts, clicks and pops. After doing some research into the matter I was advised to try a tool called DPClat to check my machine's DPC latency. Sure enough, the tool revealed that whilst DPC latency was generally fairly low, there are frequent spikes of 8000 microseconds or more which coincide with the audio dropouts:



In an attempt to solve the problem, I have tried:

Disabling every device driver in the device manager (except for system devices and the system HDD and controller)
Updating the BIOS from A03 to A10
Updating the HDD and GFX drivers to the latest versions
Turning the level of GFX accelleration down to none
Disabling system restore
Changing performance option to favour background services instead of programs
Disabling "Powermizer" feature of NVidia graphics
Disabling external PCI checking, COM & Printer port, Wifi, LAN, CPU Speedstepping, CPU dynamic accelleration, USB ports and execution prevention from the BIOS
Fixing the laptop's fan speed using I8KGUI
None of these made the slightest bit of difference to the DPC latency spikes. I have contacted Dell but all they could tell me was that they couldn't help but to install XPerf to try to trace the problem, however this doesn't seem to work with Windows XP.

I am running out of ideas and am seemingly no closer to solving this problem. The laptop is central to our live rig and our first gig is a festival appearance and only weeks away!! Whilst I am fairly technically-minded I am no computer expert, so if any of you can suggest anything which might help then please let me know...I'm losing a lot of hair over this!!!

much appreciated
Dom FTL

 

Have you updated any other drivers, such as the chipset drivers, LAN drivers, audio drivers or any other low level devices? There must be a buggy driver or something, like the latency checker suggested.

-J.B.

 

try using RMCLOCK to lock the multiplier to the highest value...

the spikes may be a result of speed-stepping which is the CPU slowing down when not under heavy load....

when the CPU speeds up or down it could be causing the spikes

see the UNDER VOLTING GUIDE

post questions in there about how to achieve the disabling of speed-step

 

I'm not much of an audio guy, but... have you looked into ASIO? It's supposed to be a low-latency audio thingy. Check it out here: http://en.wikipedia.org/wiki/Audio_Stream_Input/Output
There are some links at the bottom of the Wikipedia page that might help you... I'd start with trying ASIO4ALL.
Alternatively, Windows Vista is supposed to have a low-latency audio mixer built in if I understand correctly. I'm not suggesting buying Vista for this purpose, as there are ways to get low-latency audio on XP as I described above... but if you happen to have access to a copy of Vista, it could be an easy solution.

Also, there are probably better forums for discussing this stuff... people in audio-related forums would know lots of stuff that people here including me don't really know about.

 

Thanks for the replies

I've tried updating chipset, LAN, wireless, bluetooth, audio, HDD controller and GFX drivers, and I have also disabled every driver except for the system devices and the system HDD controller from the device manager

i also ran the computer with CPU speedstepping disabled in the BIOS, but that didn't make any difference. I'll try what you suggest though Bigozone, thanks for that.

Swarmer, my applications are already using ASIO drivers via my novation nio audio interface. ASIO4All suffers from less glitches, and although it claims latency of 12ms or so, the real-world latency of it isn't as good, and not short enough to play softsynths live.

Does anyone here know anything about RATTV3? I've installed it and it's been monitoring my system for a while, but I don't know enough about it to know how to interpret the results to find out what is causing the problem

 

Try using SysInternals' Process Explorer utility to identify more precisely which process(es) are generating the excess latency.

Also, have you followed through on all of the suggestions from the Sound on Sound forum thread to which you posted the same question?

In particular, from the text you posted above, you don't seem to have explored any issues regarding the battery (e.g., taking the battery out and running solely on the A/C Adapter) or grounding problems in the wiring into which your a/c adapter is plugged - try getting a ground loop eliminator, which is supposed to filter out power cycling noise, such as the Ebtech Hum Eliminator[/ur] or the Line Shifter, which also contains a hum eliminator. This would be a particularly good idea if, as a result of using SysInternal's Process Explorer, you find that some process related to the power/battery management system is causing, or is related to, the excessive latency you're experiencing.

 

seconded on the battery - just discovered that sorted out a similar but less severe problem on my Zepto...

In Device Manager, disable ACPI-compatbile battery (when on AC power), and try dpclat again... worked for me.

 

Ahh, it turns out that merely disabling the battery in device manager isn't enough. Indeed if I physically remove the battery form the laptop then the spikes disappear whilst the machine is idle.

As soon as I start doing anything however (even just browsing the HD) the spikes return. I tried fixing the fan speeds using I8Kfangui but this didn't seem to work as the guy on the SOS forum described.

I don[t know much about the subject, but I'm wondering if this could be something to do with ACPI. Would it be advisable to uninstall ACPI and use "standard PC" instead? Also is it safe to do this? I really can't afford to break my windows installation at this stage as I have too many gigs coming up

 

Well, first, you really should have a backup clone copy of your entire hdd before you start monkeying around under the hood if the thing is too sensitive to risk a loss that requires reinstallation. Use something like Acronis True Image Home to make a complete backup image that can be used to get you back to where you are now.

Once you've done that, I'd say give it a try disabling ACPI - if you're going to be running the thing on A/C adapter when you're performing, then you really don't have to have ACPI enabled - at least as far as I know. However, turning it off might cause some hiccups, particularly with plug-n-play components, so I would test it with inserting and ejecting any USB or other pnp devices you typically use, and I would almost certainly not insert or eject any USB or pnp device during your performance if you disable ACPI for that performance.

 

Hi, guys. I have the same issue like the one explained in this thread but in an Inspiron 1525, XP SP3. My spikes are only in the yellow zone, about 2 times a minute, on top of a smooth green background of 180 microseconds. I cannot detect the sourse of these spikes and i tried disabling everything, removing the batt, etc.
I am blaming it on a faulty implementation of the BIOS. I have the latest version available for this laptop.
There is also a weird behaviour with the DPC latency checker, namely when I installed more things in the XP, like Ableton Live, drivers for the sound cards, etc, the average of the latencies went down to below 100 microseconds, although the yellow spikes do still appear regularly. How can it be that with more processes running, the total DPC latency decreases? I came across other forums reporting the same weird behavior.

Achtern Styg

 

Probably because, prior to adding the additional processes, you weren't using 100% of the capacity of the CPU, so there were spare CPU cycles to be used by those processes, and the added processes generate deferred procedure calls ("DPCs") that, on average, have less latency than the processes that were running prior to the addition of those extra processes; effectively, those new processes slotted into the available CPU cycles without causing any of the pre-existing DPCs to be further deferred.

 

Hi, Shyster. Thanks for your reply.
My CPU is in both cases extremely little used and I using Speedswitch to maximize performance. I understand what you were saying, but i have a hard time agreeing with it
Cheers,
Achtern Styg

 

I am thinking that it's probably something to do with the BIOS too, as I've tried nearly everything else. Unfortunately Dell Tech Support have told me (after a long email conversation and many suggestions which I have listed here) that they can't help me

Looks like I'll be in the market for another laptop soon

 

What additional processes may this be?
I have the same problem with DCP spikes (over 1000 microseconds) that generates audio problem.
Running Vista 32 Home Premium. BM Asus P5Q, CPU Quad core E6600. Geforce 8800, HDD 2xWD Raptor150.

Is there any way to disable this processes that occur when OS or CPU under low load. I tried using process explorer but can not find the source.

Thanks in advance and sorry for bad English.
/op

 

I don't know what "additional processes" might be running on anyone's particular system, so I can't tell you that. However, there are, in very general terms, three things that affect the amount of latency generated by a deferred procedure call ("DPC") from a particular process: the relative priority of that call relative to all other processes running at the time, the amount of CPU cycles the DPC needs to finish its business, and the extent to which that process either locks resources needed by other processes or the extent to which it has to wait for resources that have been locked by another process.

Generally, DPCs are given a fixed priority level that is the same for all DPCs regardless of the priority given to the process that made the DPC, so that will generally not give rise to any variation in DPC latency.

In terms of the other factors, you could have a situation where you add an additional running process but it doesn't cause an increase in the latency of a particular DPC. For example, assume that you have a process that makes a DPC that gives rise to a latency of x cycles because it has to wait for an I/O process to complete that has a higher priority, and has a lock on a resource that the DPC needs to access. However, while that particular I/O process may keep the resource in question locked for x cycles (assume the resource is a file for simplicity), it doesn't actually need to consume x cycles of CPU time, only, say, x/2 CPU cycles.

If you then introduce another process that also has higher priority than the DPC, but equal priority with the I/O process in question (perhaps another I/O process that does not need to access the resource that the first I/O process has locked), and that only needs x/3 cycles to complete its business, then, because there are still x/2 cycles available for use by another process during the x-cycles for which the DPC is blocked, that second I/O process can be slotted into the time left over by the I/O process that's blocking the DPC, and the second I/O process will be completed without having to extend the number of cycles during which the underlying DPC is blocked. As a result, adding that second I/O process is not going to extend the amount of latency suffered by the underlying DPC; however, because you now have 3 processes running instead of 2, the average latency per process will drop.

 

Thank you Shyster1!

Really appreciate your post. I have learned something about DCP latency.

Beginning to understand that I know to little to even ask the right questions.

Just want a system that don't gives me audio artifacts. Bought all new hardware just to get rid off the problem but it has not worked. Hope I can blame Vista and bad driver coding for the problem.

/op