On Sat, May 02, 2015 at 08:30:50AM +0000, dave(a)661.org wrote: Hold on, weren't you the guy who couldn't mix two audio streams into one three days ago, and now you want to address surround? How about taking a step back and getting the basics, first? Correct surround sound is a delicate subject, and entire companies have been founded to get it right. If you really want to, read some basics about positioning sound sources, maybe start with the many papers on spatial audio from the past Linux Audio Conferences. It won't get you anywhere near, but it will get you started. Expect some math to be involved in this. No. Upmixing from stereo to any kind of surround can be arbitrarily complex. If you want it centered, send it to front-left, front-right, rear-left and rear-right with different gains depending on your desired position. Sum it to mono and apply an LPF with an appropriate cut-off for your .1 bass channel. Quite the contrary, the industry is already doing it: http://www.iosono-sound.com/game-audio/ Have you already figured out what mix buffers are and how you keep a single stereo stream open that is fed from multiple sources? To save you some time, here's how to do it properly: * keep the stream open all the time - send zeroes if you have nothing to output * don't rely on external software (like pulse) for mixing multiple streams. That said, send a single stereo stream from your application. * use float32 as the internal representation, with audio normalised to -1.0 .. 1.0. * mixing is adding two floats: float a, b, mix; mix = a + b; * volume is multiplying with a scalar (usually 0..1, occasionally larger): float in, out, gain; out = in * gain; * you might find non-interleaved channels easier to handle: float left[512], right[512] instead of float stereo[1024] * ask your libs (like libsndfile) to return you floats, then sum the individual buffers and hand the result to the output stream. If need be, lower the volume as a final step. * use power-of-two block sizes. Not strictly necessary but convenient. * Keep an eye on SIMD All in one: float lout[512], rout[512]; float output_gain = 0.5; for i=0; i < bufszie; i++ { lout[i] = lsrc1[i] + lsrc2[i] ... // potentially another for loop rout[i] = rsrc1[i] + rsrc1[i] ... lout[i] *= output_gain; // or fold into line about rout[i] *= output_gain; } If you have many sources, you will ultimately write a matrix mixer. You have N inputs an M outputs. Your NxM matrix then holds the gain values that express how much of input n should go to output m. Zero means nothing, one is "all". M will most likely be two (stereo). If you're striving for perfection, mind cache efficiency and the order in which you nest the loops. The float buffers are contiguous and hence benefit from hardware prefetching if you traverse them linearly. Cheers and good luck -- mail: adi(a)thur.de http://adi.thur.de PGP/GPG: key via keyserver