Author Topic: What Causes Crashed/Glitched Digital Audio Motorboating?  (Read 321 times)

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Online Cyberdragon

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What Causes Crashed/Glitched Digital Audio Motorboating?
« on: June 30, 2018, 02:35:54 am »
I haven't been able to find an actual technical answer, just "fixes" and whatnot on forums. It might be because it's not called "motorboating" or something if it's not analog so I don't know how to find it. ::)

I'm interested in the reason (digital system wise) why when a system with digital audio (such as a PC) crashes, overloads, or encounters a problem where it locks up (freezes) while playing audio it sometimes starts repeating the last few samples on loop (resulting in an engine-like purr). Why would it repeat instead of just stopping? Is is because the file reading system gets caught in a loop due to the code lock-up? Or is it something weird going on in the hardware?
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Online blueskull

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Re: What Causes Crashed/Glitched Digital Audio Motorboating?
« Reply #1 on: June 30, 2018, 02:41:31 am »
The hardware clocks out data from a buffer, when buffer is empty, it triggers DMA to copy data from main memory. Now, if the system dies, there's no response from DMA, so the audio system clocks data from the same buffer over and over again.

Similarly, if the DMA still works, it still can't get new data from audio driver, so it repeats the same buffer in audio driver's RAM buffer space without getting updated.
 
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