Sound latency?

[jan-kleks]

This is a really great project! Does it add sound latency due to the fact there is an additional emulation layer? If yes, how much?

[crazii]

Yes, the emulated DMA transfer may not start immediately, but after about 0~5ms.

[jan-kleks]

Hmm... I guess it is neglectable then in comparison to the latency you would get running an emulator on a modern OS?

[crazii]

I overlooked the total buffering of the PCI sound card. with the total buffering size as 16384 bytes, and with format as 16bit PCM, stereo, 22050Hz, the delay will be 0~180ms, which is noticeable.

[crazii]

the last update (beta2b) reduces the latency to an acceptable value, (10~20ms) you can try it at: https://www.vogons.org/viewtopic.php?f=62&t=93006

[jan-kleks]

This is awesome! Thank you! I think it should be totally fine now... But if there is room for pushing the latency even further down without breaking SBEMU (at least on more powerful hardware) -- go for it! Of course, I mean, at some point in the future when other more important issues are ironed out...

[jan-kleks]

@crazii At this stage of the project can we theoretically reduce the buffering even further? -- For even lower latency. :)

[crazii]

@crazii At this stage of the project can we theoretically reduce the buffering even further? -- For even lower latency. :)

Theoretically yes, but if smaller buffer are used, the sound might becomes stuttering - the sound card finishes playingback the buffer too fast that there's no more buffer for it.

It's a common dilemma in sound buffering that requires real-time reaction: large buffer may cause latency and yet too small buffer might cause stuttering.
If no real-time reaction is needed (i.e. playing a music), then the buffer could be as large as possible and it doesn't matter.

As you can read dosbox-x.conf, in [mixer] section's comments:

#       blocksize: Mixer block size, larger blocks might help sound stuttering but sound will also be more lagged.

[jan-kleks]

@crazii I see, thank you for this detailed explanation! So how does SBEMU sound latency compare to real cards it emulates?