What is DPC Latency?

[djgizmo]

What is DPC Latency?

From what I know about it, is if it is too high, it causes audio drop outs / pops / crackles.

The reason I ask, is I have a dell 6400 I bought over a year ago. Specifically for DJ'ing with Torq Xponent. No matter what, I have high DPC latency. I've tried Win XP & Windows 7 (both work fine) but my latency hovers around the 150us mark and spikes to the 2000us mark every 30 seconds. I've pulled the battery, turned off speedstep, wifi, cdrom, turned off every service that can safely be turned off and still get that spike. If I have Torq open and I'm playing music, i'll get a pop in the audio during that spike.

This is all without a single program open, including AV.

My business IBM laptop on the other hand, I'm using right now to write this has a typical latency of 40-100 with peaks at 700us. I've not disabled a thing on this IBM.

What hardware affects this latency?

I'd like to replace my laptop this year with something that will fit my needs a bit better.

Can anyone assist?

Thanks!

Sean

[TheLoud1Please]

did you turn off wifi?

[StereoPari]

Hey,

There is a DPC latency checker utility which you can download somewhere from the web. I don't remember if it shows which applications are requesting I/O's at a given time, but at least Microsoft should have a tool for that. Download a utility which shows you the I/O requests so you can see what application (it can be a driver, windows component, peripheral component etc) is the bad apple. Then work your way up from there and try to fix the problem.

Sorry I don't now remember actually where to download them, but there are tools for this problem on the web and they shouldn't be hard to find. Hope this helps...!

[djgizmo]

I've turned off wifi, but still the spike continues.

As for the MS tool. I believe its called the Windows Performance Kit tool.

I'm unsure how to run it to get the information you mentioned. I have run common DPC Latency Checker (which is where I received my info so far) and its not helped me pinpoint anything yet.

[Blinddot]

This is where you can download the DPC latency checker

DPC Latency Checker

and this is technical info about DPC latency

DPC Latency Checker

The most usual reason for high DPC latency peaks is a conflict between two hardware devices, usually the sound card and something else. You should disable WiFi, LAN, USB controllers, TV cards etc.. one at a time and do the cheking again, in order to find out which is the one getting you in trouble. A good hint is to look at the IRQ sharing, many non-PCIe hardware devices don't like to share IRQ, and by just changing the PCI slot (if possible) you could just fix the problem. Also you should disable in the Bios all the devices you wont be using, like serial and parallel ports, joystick/midi ports, extra hard disk controllers (I recommend to use the chipset one only), integrated modems and sound cards etc.. this disabling will free up a few IRQs and will probably help you with the IRQ sharing issue.

[theblue1]

Yeah... those figures are high. I just checked my old Dell beater box (a 2.8 gHz P4 with 3 audio interfaces, mobo, PCI, and FW, one each) and its latency figures using that checker and, even with two browsers and the not-necessarily-light-on-its-feet Rhapsody streaming player rolling in the background, my max latency figure stays well under a 100 microseconds -- until I switch tasks, which can cause it to jump into the hundreds, mostly hovering in the 150 microsecond range, although I did manage to get it to go up to around 560 at one point. Right now, I'm switching back and forth between FF, Rhapsody and the DPC checker and the max is holding about 173. (I've reset it a few times to get new max results from different operations.) Current latency seems to range from single digits to the 50-60 microsecond range.

[After letting it run for some minutes and bouncing around, I saw a max figure of just under 670. Again, though, I've got IE and FF open (and FF has 10 tabbed windows open), as well as the Rhapsody player streaming music off their servers to me.]

[UPDATE: I have my machine on the network via ethernet and did have the WiFi disabled. So I decided to enable the WiFi but leave the ethernet connected and enabled. Switching to the system connections inteface shot the max up above 1500 microseconds (1.5 ms, to those of us who think in the long scale). Interestingly, my current usage indicator went from the 9-55 microsecond range to 90-150. I'm assuming that had the WiFi found a connection and set it up, its CPU usage would presumably drop some. I'll try that later, perhaps. But it does seem to suggest that, surprise, surprise, the hard-wired ethernet network connection may be less of a drain on resources. Certainly, searching for a WiFi connection definitely takes some CPU cycles. And, as expected, disabling the WiFi in Network Connections dropped the DPC latency current usage way down again.]

[djgizmo]

Originally Posted by Blinddot

This is where you can download the DPC latency checker

DPC Latency Checker

and this is technical info about DPC latency

DPC Latency Checker

The most usual reason for high DPC latency peaks is a conflict between two hardware devices, usually the sound card and something else. You should disable WiFi, LAN, USB controllers, TV cards etc.. one at a time and do the cheking again, in order to find out which is the one getting you in trouble. A good hint is to look at the IRQ sharing, many non-PCIe hardware devices don't like to share IRQ, and by just changing the PCI slot (if possible) you could just fix the problem. Also you should disable in the Bios all the devices you wont be using, like serial and parallel ports, joystick/midi ports, extra hard disk controllers (I recommend to use the chipset one only), integrated modems and sound cards etc.. this disabling will free up a few IRQs and will probably help you with the IRQ sharing issue.

I've used this tool before, as stated in the thread. (3x now)

This issue is dealing with a laptop, not a desktop, so changing pci slots is not an option.
As stated before, I've disabled wifi. The laptop has no tv cards. Disabling USB is not an option. Disabling ports / harddrive controllers in a dell laptop bios is commonly a no go.

From what you're trying to say is that DPC Latencies are caused by IRQ sharing?

[theblue1]

Let's take another angle...

How many background services are running when no applications are opened and running? (In XP, ctrl-alt-delete to bring up the Task Manager, Processes tab.) How much RAM is it taking just sitting there? (Commit charge, bottom of the tabbed interface.) And how many services are running after boot up is completed but before you run any applications; how much RAM is being used? If there are a lot of processes listed (more than 25 or 30 might be considered a lot -- but I've seen brand new machines so loaded with crapware from big vendors like Sony, HP, Dell, etc, that they had 70 or 80 services running after booting up and RAM usage was over 300 MB just sitting there waiting to get started!

For reference, a fresh, clean install of XP can have a RAM footprint after booting up as low as the low 60 MB range. I can't remember how many services a fresh install will have running, but my guess is around 20.

On big vendor machines, I have been known to just open up MSConfig (Start menu/run/ type in MSConfig ), go to the services tab, click "hide all Microsoft services" and uncheck everything that I didn't know was required (like a WiFi driver or such). Ditto the Startup tab. All the crapware like qttask (some absolutely unnecessary QuickTime 'helper' app), jusched (the bloated and idiotic Sun Java updater, which can take as much as 12-15 MB just sitting there waiting for a Java update that might come next year), etc -- I just uncheck 'em all, unless it's something I know should be running from startup. And, guess what, on my machine, that's none of them. (Well, except maybe ctfmon, which always just turns itself back on, anyhow.)

[djgizmo]

Originally Posted by theblue1

Let's take another angle...

How many background services are running when no applications are opened and running? (In XP, ctrl-alt-delete to bring up the Task Manager, Processes tab.) How much RAM is it taking just sitting there? (Commit charge, bottom of the tabbed interface.) And how many services are running after boot up is completed but before you run any applications; how much RAM is being used? If there are a lot of processes listed (more than 25 or 30 might be considered a lot -- but I've seen brand new machines so loaded with crapware from big vendors like Sony, HP, Dell, etc, that they had 70 or 80 services running after booting up and RAM usage was over 300 MB just sitting there waiting to get started!

For reference, a fresh, clean install of XP can have a RAM footprint after booting up as low as the low 60 MB range. I can't remember how many services a fresh install will have running, but my guess is around 20.

On big vendor machines, I have been known to just open up MSConfig (Start menu/run/ type in MSConfig ), go to the services tab, click "hide all Microsoft services" and uncheck everything that I didn't know was required (like a WiFi driver or such). Ditto the Startup tab. All the crapware like qttask (some absolutely unnecessary QuickTime 'helper' app), jusched (the bloated and idiotic Sun Java updater, which can take as much as 12-15 MB just sitting there waiting for a Java update that might come next year), etc -- I just uncheck 'em all, unless it's something I know should be running from startup. And, guess what, on my machine, that's none of them. (Well, except maybe ctfmon, which always just turns itself back on, anyhow.)

I don't mean to be insulting, but how does memory have direct effect on DPC Latency?

No one has defined DPC Latency for me yet.

From what I've been researching, DPC Latency has to do with response from the CPU or other devices in the pc of concern. When the device or cpu do not respond, DPC latency spikes occur.

Yea, I know the bastard children known as jusched and qtask.

When I'm running DPC latency checker, only 10-12 background process show.

Currently I'm running Windows 7 and don 't feel like reformatting again as the latency is similar to XP.

I wish I knew which specific components dell may have skimped on to cause this latency. Some people don't have to disable anything and their latency is picture perfect.

[StereoPari]

Originally Posted by djgizmo

I wish I knew which specific components dell may have skimped on to cause this latency. Some people don't have to disable anything and their latency is picture perfect.

Of course, you should use ASIO drivers. Are you using ASIO?

[Audiop]

Some machines and BIOS are simply not made for streaming audio.I've had a lot of problem of all that crap and even with ASIO I can have some problems.

Someone should design an audio and measurement oriented laptop (no movable parts ie. no fans and no spinning discs) with dedicated OS/software so all the millions of people into this can have troublefree portable audio.

I'm so fed with Win XP but I'm not sure the Mac route is the solution either, seems like people experience almsot as much problems on Mac's.

A specialty built PC running Linux is tempting but then you run into problems finding software and drivers for some hardware.

All this crap should be a thing of the past really... *puke*


Ok, thanks for listening, I fell much better now!



/Peter

[manning1]

i was showing a guy who sells retail laptops dpc latency checker a few months back.
he is also into recording..nice guy.
every name brand lappie we tried had spikes in the store.
i personally think its gonna need another technology round before these things get decent.
so moi is staying away.
staying desktop.

[hugol]

Originally Posted by djgizmo

I don't mean to be insulting, but how does memory have direct effect on DPC Latency?

No one has defined DPC Latency for me yet.

From what I've been researching, DPC Latency has to do with response from the CPU or other devices in the pc of concern. When the device or cpu do not respond, DPC latency spikes occur.

Yea, I know the bastard children known as jusched and qtask.

When I'm running DPC latency checker, only 10-12 background process show.

Currently I'm running Windows 7 and don 't feel like reformatting again as the latency is similar to XP.

I wish I knew which specific components dell may have skimped on to cause this latency. Some people don't have to disable anything and their latency is picture perfect.

Ok I'll have a go - and I'm sure someone will jump in to correct if I get any details wrong And it hasn't got anything to do with background processes - it's about device drivers - it's a software problem. A dodgy BIOS can also cause issues (Gigabyte had problems for a while with some P35 board BIOS versions for example).

Deferred Procedure Calls are basically a mechanism with which Windows handles interrupt servicing. As you might know interrupts are a mechanism with which devices can proactively signal they need attention from the processor - e.g. data is available. IRQ lines (Interrupt ReQuest) are the hardware mechanism that supports this.

Hundreds or thousands of interrupts are occuring every second within a PC. Windows needs to manage and prioritise these - critical interrupts might be handled in full immediately, whereas lower priority requests will be queued - and this is where DPCs come in. Windows will acknlowledge the interrupt and queue it - and come back to actually do something about it later.

An interrupt from an audio interface (to say there is some audio data available) isn't considered critical. The driver uses the DPC mechanism in Windows along with most other devices. So even if the audio interface needs data for its buffer (for output) or has data avaialble in its buffer (for input) the actual audio driver code that will move this data isn't actually invoked till Windows gets round to processing the relevant DPC item on the queue.

This is where problems can occur. Windows will process other things ahead in the queue before servicing the audio request. If (other) drivers are badly implemented they can use too much processing time delaying processing of our audio request (our audio driver can also use too much time). Clearly as audio is time critical if there is too much of a delay before data transfer occurs the audio buffer may empty (output) or overflow (input) - therefore audible pops and clicks occur. Obviously this is why having a bigger buffer helps.

The DPC latency tool just measures how much time is being spent servicing DPCs - i.e. how long all the drivers are actually taking to do their required DPC processing. Obviously we want a low as possible value which indicates all the drivers are well written and efficient - the lower the value the less likelihood that they'll prevent timely audio data transfer and the better chance of being able to use smaller buffer sizes for lower latency without pops and clicks.

[Absolute]

First, programs being opened usually doesnt mean anything--its a component. BTW..you should not have any peaks--700 is still a problem for audio and video. Honestly..stop trying to understand it because its not gonna help. Its just confusing you because it has nothing to do with any processes running. I know very little about its fine details and have fixed this problem more than once.

I know how you feel man..this is total BS--total neglect from hack component makers.

Laptops are riddled with DPC problems to the point where many honest manufacturers will warn against using them

It is usually the USB or the network card or chip looking for access. The spikes are caused by terrible designs, errors in hardware or software controlling the hardware, or just a plain disregard for audio

I have found that #3 is the most common. They just dont have enough DAW users to justify fixing these things.

One things many new DAW users dont understand is there are only a few machines that actually work flawlessly with audio. The Intel P5k, P35, and P5b being a few of them. These motherboard chipsets take audio into account or just got lucky. Either way--if you use one of these motherboards and have a DPC problem it will almost always be the Video card or an add-on card

Some Nvidia cards cause huge DPC spikes--a few ATI's too. Boot up with the generic VGA driver and test--or stick in an old video card

This is how to find the problem djgizmo---by disabling and removing each one by one. It can even be a wireless keyboard. If its your mother boards chip set you probably screwed but you can try disabling each USB hub etc in your operating system but search your chipset on the web under audio pops and crackles and you will quickly find out if its a big offender---the bad news is most chipsets except a few are going to cause some type of problem

If you know any daw builder they know this topic like the back of their hands--they know what to use and the boatload of components to avoid

[Gordon]

here's a conundrum . . .

Same hardware, in XP I get a typical DPC latency of about 9 microseconds. In Windows 7 64 it's about 100.

Asus P6T
I7 920
6 GB Corsair 1600MHz RAM
Profire 2626

[StereoPari]

Originally Posted by djgizmo

I've turned off wifi, but still the spike continues.

As for the MS tool. I believe its called the Windows Performance Kit tool.

I'm unsure how to run it to get the information you mentioned. I have run common DPC Latency Checker (which is where I received my info so far) and its not helped me pinpoint anything yet.

Hey I found the tool I was referring to:

Process Monitor

If you use both the DPC latency checker and this one, you'll probably see what's causing those spikes.

I'm on Win XP and have managed to get a pretty solid system by turning off lots of processes. You have to be careful tho, and make notes about the changes you've made -in case something goes wrong, that's your insurance.

[Styxx]

I realise that this thread is about a year and a half old, but I've found it through Google while trying to sort some shit out on my PC and thus far it's been fairly helpful. I downloaded the latency checker and it checked all the latencies which are most definitely there for the checking. Now I'm looking for a solution. I'm reasonably sure that the issue I'm having is with my wireless card, but I want to be sure before taking any action, so I tried downloading that process monitor in StereoPari's post. I ran it but there's just way too much information there and I have no idea what I'm looking at/for.

Could someone please tell me what I should be looking for with the process monitor? There's a filter on it but I don't really know what I should be filtering and what is useful information.

[jruberto]

I noticed my DPC latency was spiking to around 600 microseconds on mouse usage. Normal idle being around 10 microseconds with all non-essential stuff shut down.

Jacking the mouse directly into a USB port instead of into the USB hub cut those spikes down to 50 microseconds, much better. Might be worth checking that out if you are having DPC latency problems.

[rogerdodger]

Good advice

[fastlanestoner]

I use an HP Elitebook laptop and the DPC latency was immaculate right out of the box. After disabling what I don't need it's never let me down. Quality and priority for audio definitely differs from manufacturer to manufacturer but it's entirely possible to get a great audio machine without much tweaking.

[rksguit]

Originally Posted by hugol

Ok I'll have a go - and I'm sure someone will jump in to correct if I get any details wrong And it hasn't got anything to do with background processes - it's about device drivers - it's a software problem. A dodgy BIOS can also cause issues (Gigabyte had problems for a while with some P35 board BIOS versions for example).

Deferred Procedure Calls are basically a mechanism with which Windows handles interrupt servicing. As you might know interrupts are a mechanism with which devices can proactively signal they need attention from the processor - e.g. data is available. IRQ lines (Interrupt ReQuest) are the hardware mechanism that supports this.

Hundreds or thousands of interrupts are occuring every second within a PC. Windows needs to manage and prioritise these - critical interrupts might be handled in full immediately, whereas lower priority requests will be queued - and this is where DPCs come in. Windows will acknlowledge the interrupt and queue it - and come back to actually do something about it later.

An interrupt from an audio interface (to say there is some audio data available) isn't considered critical. The driver uses the DPC mechanism in Windows along with most other devices. So even if the audio interface needs data for its buffer (for output) or has data avaialble in its buffer (for input) the actual audio driver code that will move this data isn't actually invoked till Windows gets round to processing the relevant DPC item on the queue.

This is where problems can occur. Windows will process other things ahead in the queue before servicing the audio request. If (other) drivers are badly implemented they can use too much processing time delaying processing of our audio request (our audio driver can also use too much time). Clearly as audio is time critical if there is too much of a delay before data transfer occurs the audio buffer may empty (output) or overflow (input) - therefore audible pops and clicks occur. Obviously this is why having a bigger buffer helps.

The DPC latency tool just measures how much time is being spent servicing DPCs - i.e. how long all the drivers are actually taking to do their required DPC processing. Obviously we want a low as possible value which indicates all the drivers are well written and efficient - the lower the value the less likelihood that they'll prevent timely audio data transfer and the better chance of being able to use smaller buffer sizes for lower latency without pops and clicks.

Most accurate/realistic,response in regards to the OP's situation,too cool

[mowmow]

I had a bad experience with DELL laptop.
DPC latency issue drove me nuts.
I could not pin point the cause of the latency so finally I had to get rid of DELL and get new PC.
Latency is lower than before and drop out problem is gone.
But I still think PC really is not made for streaming audio.

[MacMacMac]

My Dell laptop works fine. But it needed an external sound card to make it so. I use a Presonus AudioBox.

[rksguit]

Originally Posted by mowmow

I had a bad experience with DELL laptop.
DPC latency issue drove me nuts.
I could not pin point the cause of the latency so finally I had to get rid of DELL and get new PC.
Latency is lower than before and drop out problem is gone.
But I still think PC really is not made for streaming audio.

Patently UN True.It depends on hardware/drivers[which PC/mac share[HW] MORE than EVER before].A lot of INFORMATION, that was across the board,even 1 year ago,is NOW utterly in-correct, as newer hardware/drivers are introduced.

Something I thought was GOSPEL,was proven WRONG today,as NEW stuff keeps the situation "ever changing"

It was VERY TRUE a Dell XPS "501x",was crap for audio,even with an RME Babyface[Cheapest/Highest Quality Interface Available] However!!!, My XPS L50"2"x[2011/latest/basic consumer/Non Workstation model]is actually fantastic BETTER than with my VERY basic,USB 1.1 interface: cakewalk/Edirol UA25-EX, with THE ON BOARD "REALTEK/JBL/WAVES maxxaudio",AND[Most Importantly] "ASIO4all".....2.4ms RTLatency[for listening only,total perfection]and 5 to 9ms RTLatency for recording[Line In].

For using with my average interface[Anything under $500....but even THAT is changing] I use an i7 2600k PC desktop [LESS than $800 in the US] overclocked @ 4.4GHz[better than stock cooling....32c temp.]TOTALLY STABLE,Ludicrous POWER, and MAN can that "PC" STREAM AUDIO.

[mowmow]

Originally Posted by rksguit

Patently UN True.It depends on hardware/drivers[which PC/mac share[HW] MORE than EVER before].A lot of INFORMATION, that was across the board,even 1 year ago,is NOW utterly in-correct, as newer hardware/drivers are introduced.Something I thought was GOSPEL,was proven WRONG today,as NEW stuff keeps the situation ever changing.It was VERY TRUE a Dell XPS "501x",was crap for audio,even with an RME Babyface[Cheapest/Highest Quality Interface Available] However!!!, My XPS L50"2"x[2011/latest/basic consumer/Non Workstation model]Is actually fantastic BETTER than with my VERY basic, USB 1.1 interface: cakewalk/Edirol UA25-EX, with THE ON BOARD "REALTEK/JBL/WAVES maxxaudio",AND[Most Importantly] "ASIO4all".....2.4ms RTLatency[for listening only,total perfection]and 5 to 9ms RTLatency for recording[Line In]. For using with my average interface[Anything under $500....but even THAT is changing] I use an i7 2600k PC desktop [LESS than $800 in the US] overclocked @ 4.4GHz[better than stock cooling....32c temp.] and MAN can that "PC" STREAM AUDIO.

I understand but you never know if your next PC will act that way. PC is designed to work with many different hardwares and different tasks which means it is not the machine dedicated for audio streaming.
Standard PC maker will never design their PC just for audio since there aren't that many audio users compare to the rest of users.
If I experience one drop out in year, I'd consider it is not so stable and not really dependable. Unless it has super performance I'd think it's a toy. But this is just me.

[rksguit]

Originally Posted by mowmow

I understand but you never know if your next PC will act that way. PC is designed to work with many different hardwares and different tasks which means it is not the machine dedicated for audio streaming.
Standard PC maker will never design their PC just for audio since there aren't that many audio users compare to the rest of users.
If I experience one drop out in year, I'd consider it is not so stable and not really dependable. Unless it has super performance I'd think it's a toy. But this is just me.

Complete mac BOLLOCKS,Macs use SAME hardware smart boy+Ina couple years Id want to upgrade anyway cause of tech improvements,+I Built my own,please,F

[DECBEATS]

Look for ways to get rid of bloatware? Thats what ive been told to do in a situation like this

[Dj K 4 Yahweh]

Originally Posted by fastlanestoner

I use an HP Elitebook laptop and the DPC latency was immaculate right out of the box. After disabling what I don't need it's never let me down. Quality and priority for audio definitely differs from manufacturer to manufacturer but it's entirely possible to get a great audio machine without much tweaking.

Hi, i'm looking for a laptop for audio recording at the momment...which model HP Elitebook laptop do u have?

Thanks!

[jruberto]

Originally Posted by DECBEATS

Look for ways to get rid of bloatware? Thats what ive been told to do in a situation like this

Depending on what a particular piece of bloatware does, it may or may not have any effect on DPC latency.

But that's a good practice for an A/V machine at any rate, just to conserve RAM and CPU resources. I'm still clinging to Windows XP on my aging DAW and when I boot clean, I have 28 processes running. Most bloated up machines that I see have more like 60 or 70 processes running, so, yeah.. do that.

[Fnx]

I had the same problem. I disabled devices one by one, and DPC latency was way beyond 1000 microsec.

Then I realised that if I stress the CPU 100%, DPC was constantly under 100 microsec. So I modified on Control panel/power options - the minimum processor state. It was on 5%. Putted on 100 and the problem was solved. No more latency. I played with that and realised that the minimum required was 55%. I'm on Windows 7 32bit.
Hope this helps..