OpenCL GPU Audio

Question

There's not much on this subject, perhaps because it isn't a good idea in the first place.

I want to create a realtime audio synthesis/processing engine that runs on the GPU. The reason for this is because I will also be using a physics library that runs on the GPU, and the audio output will be determined by the physics state. Is it true that GPU only carries audio output and can't generate it? Would this mean a large increase in latency, if I were to read the data back on the CPU and output it to the soundcard? I'm looking for a latency between 10 and 20ms in terms of the time between synthesis and playback.

Would the GPU accelerate synthesis by any worthwhile amount? I'm going to have a large number of synthesizers running at once, each of which I imagine could take up their own parallel process. AMD is coming out with GPU audio, so there must be something to this.

Answer 1

For what it's worth, I'm not sure that this idea lacks merit. If DarkZero's observation about transfer times is correct, it doesn't sound like there would be much overhead in getting audio onto the GPU for processing, even from many different input channels, and while there are probably audio operations that are not very amenable to parallelization, many are very VERY parallelizable.

It's obvious for example, that computing sine values for 128 samples of output from a sine source could be done completely in parallel. Working in blocks of that size would permit a latency of only about 3ms, which is acceptable in most digital audio applications. Similarly, the many other fundamental oscillators could be effectively parallelized. Amplitude modulation of such oscillators would be trivial. Efficient frequency modulation would be more challenging, but I would guess it is still possible.

In addition to oscillators, FIR filters are simple to parallelize, and a google search turned up some promising looking research papers (which I didn't take the trouble to read) that suggest that there are reasonable parallel approaches to IIR filter implementation. These two types of filters are fundamental to audio processing and many useful audio operations can be understood as such filters.

Wave-shaping is another task in digital audio that is embarrassingly parallel.

Even if you couldn't take an arbitrary software synth and map it effectively to the GPU, it is easy to imagine a software synthesizer constructed specifically to take advantage of the GPU's strengths, and avoid its weaknesses. A synthesizer relying exclusively on the components I have mentioned could still produce a fantastic range of sounds.

While marko is correct to point out that existing SIMD instructions can do some parallelization on the CPU, the number of inputs they can operate on at the same time pales in comparison to a good GPU.

In short, I hope you work on this and let us know what kind of results you see!