[necubi]

Audio processing is real-time, which means that you cannot miss your deadline. If you do miss you get audible glitches, whereas in graphics you just get a slowdown. For that reason, audio code is written in a very particular, real-time safe style that avoids locks, allocations, syscalls, and anything else that is not guaranteed to return within a bounded amount time.

How long the deadline is depends on your buffer size and sample rate. To my ear, buffer sizes of >128 samples (at a sample rate of 44.1 KHz) have detectable latency (although the amount of latency will depend also on how many applications are in your signal chain). At 128 samples you have just under 3ms to do your processing.

Also note that for graphics, the output is the GPU itself. So you don't need to wait for the output to move back to the CPU, it's already where it needs to be.

[viraptor]

But let's keep some realistic context. The audio output is under 1 MBps. You can push that much over original PCI (not express) and ~1ms delay on PCI was "everything must be broken, reset the whole bus". Pushing audio samples both ways on PCIe will not be an issue.

https://www.cycfi.com/2019/04/gpu-dsp-latency/

> PCI-E 3.0 standard guarantees data transfer for 4 kb data with 1-2 μsec (3-10 round trip).

Copying CPU-GPU-CPU:

> size: 8192 bytes, time: 4.72 us,

This should not be a meaningful impact in any audio workflow.

[andi999]

What OS are we talking? It sounds like you need a real time os.

[necubi]

MacOS has the ability to prioritize audio threads to avoid scheduling misses [0]. Linux has a set of patches [1] to give it soft real-time capabilities. I don't know as much about Windows, but I assume it has similar capabilities.

And it's not like this is ABS firmware, where someone might die if you miss your deadline, and where hard real-time OSes are used. But you do get glitches in the audio stream, which in performance contexts is still pretty bad.

[0] https://developer.apple.com/documentation/audiotoolbox/workg... [1] https://wiki.archlinux.org/index.php/Professional_audio#Real...

[krzepah]

What are you talking about ? Most people working with sound today do so by using a DAW like Ableton, QBase or Fruity Loop that work on Windows or sometimes Mac Os

[andi999]

Comment before was saying you cannot miss a deadline; i didnt know this was possible with windows or macos.

[viraptor]

They're not hard-realtime, so they definitely can miss a few samples. You can workaround that by reconfiguring an external device rather than generating the samples locally, but that's not what Ableton or FL do.

Win and Mac have soft-realtime scheduling and the mentioned software does what it can without guarantees https://help.ableton.com/hc/en-us/articles/209072289-How-to-... I've been to a live gig before where the performance was paused a few times because artist's mac was misbehaving.