Hacking the PSP Blog

StrmnNrmn on Daedalus Audio Support

So, back to audio support in Daedalus. I had come to the point with implementing various dynarec improvements that I felt it was worth looking into audio to get an idea how how well it would work, and how much of a performance hit there was. As I was saying, one of the reasons I'd been putting off implementing audio support was that I knew that taking a high-level approach was going to be time consuming and error prone. The alternative, low level emulation, just wasn't practical from a performance point of view.

In the end, I decided to see if I could find the source for a PC audio plugin, and adapt this for use with Daedalus. I was fortunate enough to discover that Azimer had made the source for v0.55 of his audio plugin available (Azimer - if you're reading this, please drop me a line to say hello :) My reasoning was that if I could get something up and running in a couple of evenings then I could figure out how much work would be involved in getting it polished. If it looked like it was going to be too much work then I could revert all my changes and at most I'd have wasted just a few hours.

In the end it all went incredibly well. Azimer's source was very self-contained, with just a couple of hooks to implement to get it working. There were a few small issues to solve like having to upsample the output to 44.1KHz (as the PSP output is fixed at this frequency), but nothing that took more than a couple of hours.

So, how does it sound? Well, it's pretty variable. It sounds great in places where there's a high enough framerate to keep the audio buffer full. Mario 64 is pretty good for this - it seems 25fps is a minimum to avoid any choppiness in the output. When the framerate drops lower than this the audio quality does start to suffer significantly. On the plus side, it seems to be decoding everything correctly in all the roms

Which brings me to my next point - how does enabling audio support affect the performance of the emulator? I've not had chance to measure this empirically, but it probably slows things down by about 10-20%. Given that R9 is running about 40-100% faster than R8, you should be able to run R9 with audio and still see a small speedup. In any case, I've added an option to enable or disable the audio in the front-end (this is also accessible from the pause menu while the rom is running). I've tested so for, which means that the quality is only going to improve as I make further improvements to the performance of the emulator.