So why DOES sound loop when your system hangs?

[Steve]

A friend and I were discussing this a while ago, and it just popped back into my head.

And what the hell, I thought I'd share it with you.

Your sound card, or more likely your sound card's driver, reads data from a portion of memory allocated as an output buffer for your audio. It's a ring buffer.

That means, the sound card plays whatever's in there, and when it gets to the end of the section of memory, it jumps back to the beginning and carries on.

So, as long as your system can update what's already been read before it gets read again, you won't get sound-looping.

But if something goes wrong and your system becomes less responsive than it should be... the buffer under-runs, and because it's a ring buffer it just keeps getting read out.

This post was brought to you by the fact that I'm a nerd, and wanted to show it.

[Hicks12]

Dont know why but tis popped into me head just now, wierd thought since im a bit tipsy atmmm. My sound card seems to hage died or not fitted in properly after movn it to fit a zalman fans adaptor, will have to check it later cos its causin pc to freeze randomly.

[SiM]

Interesting, although they must be able to make a workaround for it because it is damn annoying.

[Steve]

Why would you work around something that only happens once something else is already broken, and goes away when that broken thing is fixed?

[SiM]

Why would you work around something that only happens once something else is already broken, and goes away when that broken thing is fixed?

Well surely the sound card drivers can prevent it from looping when crashing. Its not something that hugely important but it would be nice imo. There is no real reason to work around it - I just find it rubs salt into the wound when something is wrong because its annoying.

Actually, thinking about it bsod crashes normally don't suffer from this sound loop iirc

[Steve]

But there's no way for them to know if the buffer is underrun... not without incurring a large overhead.

As for BSOD, they're generally a STOP error, and so stuff... erm... stops.

[SiM]

But there's no way for them to know if the buffer is underrun... not without incurring a large overhead.

As for BSOD, they're generally a STOP error, and so stuff... erm... stops.

Can't they just put some logic in saying that if the same thing is played twice then stop playing? I am not a programmer so I don't know if this is possible... I guess its one of those things that is easier said than done. Oh well, my comment about the workaround was just a random thought, don't read too much into it

[pauldarkside]

Can't they just put some logic in saying that if the same thing is played twice then stop playing? I am not a programmer so I don't know if this is possible... I guess its one of those things that is easier said than done. Oh well, my comment about the workaround was just a random thought, don't read too much into it

But if everything's stopped (processes halted and further ones are not allowed) how would you check if it's still running after a crash like that... Your sound processor won't be given the instruction to flush the buffer and the "play" process is likely handled by the sound processor so until it's told it won't know.

Edit: At least that's what I'd imagine is going on.

[SiM]

But if everything's stopped (processes halted and further ones are not allowed) how would you check if it's still running after a crash like that... Your sound processor won't be given the instruction to flush the buffer and the "play" process is likely handled by the sound processor so until it's told it won't know.

Edit: At least that's what I'd imagine is going on.

Maybe the sound chip can check on a hardware level?

[pauldarkside]

Maybe the sound chip can check on a hardware level?

Where is it going to get the instruction or confirmation from if the system has been suspended, even if it could then how without wasting valuable resources? Imagine if it didn't work like that (working how you mentioned earlier) and the sound chip was told to loop the buffer (small midi stuff for example) and the system crashed - it would only know if something had gone belly-up if it was constantly checking via a timer.

Besides, it's the default in Windows set to automatically reboot upon a critical system failure? I seem to remember some version having that.

[SiM]

Where is it going to get the instruction or confirmation from if the system has been suspended, even if it could then how without wasting valuable resources? Imagine if it didn't work like that (working how you mentioned earlier) and the sound chip was told to loop the buffer (small midi stuff for example) and the system crashed - it would only know if something had gone belly-up if it was constantly checking via a timer.

Besides, it's the default in Windows set to automatically reboot upon a critical system failure? I seem to remember some version having that.

Chill dude, no detailed analysis required... I was just saying a random thought! I thought that it would be possible given the technology of today, that is all... I am not a software or hardware developer, just a normal dude

[pauldarkside]

Chill dude, no detailed analysis required... I was just saying a random thought! I thought that it would be possible given the technology of today, that is all... I am not a software or hardware developer, just a normal dude

Umm

At least that's what I'd imagine is going on.

And I'll add that I couldn't be more chilled even if I was sedated. After a couple of schmokes, no pancakes - I'll have them later, I'm really not bothered. Kind of keeping myself entertained before heading out. Been a couple of tough weeks

PS I was actually quite shocked not to find any poon, not even a smidgen of tang, on those two hard drives! You're letting yourself go dude

[SiM]

And I'll add that I couldn't be more chilled even if I was sedated. After a couple of schmokes, no pancakes - I'll have them later, I'm really not bothered. Kind of keeping myself entertained before heading out. Been a couple of tough weeks

Well what I really meant was that there was no need to over analyse my random thought...

PS I was actually quite shocked not to find any poon, not even a smidgen of tang, on those two hard drives! You're letting yourself go dude

Well they wouldn't be new if I had done that
But I am sure you will have fun filling them up on your own

[TheAnimus]

ok, you really want to know?

what effectively happens when a PC 'hangs' is that certain level of prioty tasks don't get executed.

We must all of seen PCs (espesually pre NT days) hang with the mouse still working, or the keybord caps lock key still toggling the LED?

This is because PCs have certain levels of important for the preodic tasks (called 'interupts'). Multi-Media is one of the highest level tasks, with something like a timer for a GUI app like the task manager graph in windows, been one of the lowest.

What happens is the device driver that 'runs' the soundcard is a high priority, and able to keep going, but the application thats feeding it, can't. So this means the soundcard can continue to operate, but will not get new data.

Now as to why it loops, when you put sound out to the sound card, your marshalling memory from application A to device driver Z, marshalling accross a boundry is always computationally expensive, even more so when your sharing large amounts of memory. So on windows you have two buffers. The idea is whilst the driver is playing buffer 1, app is loading up buffer 2. and vice versa.

Now what happens is the device driver can keep playing these buffers, but the app thats stacking the data in, can't keep stacking the data in. Hey presto, sound loops.

This can be really common if you've got an application that makes an assumption like, the HDD i'm reading this data off, will always be able to keep up with my read rate.

So tried to keep that simple and un-technical

[Virtual Monkey]

I'd never really considered it before, but it's actually pretty interesting.

[badass]

Useless to me and yet interesting at the same time