objective c - Can't set multiple musical instruments in iOS using MusicPlayer and AUGraph -

i have musicplayer holds musicsequence containing 3 musictracks. have set augraph 3 ausampler nodes plugged multichannel mixer, in turn connected output node.

i using soundfont, , 3 different musictracks play on 3 different musical instruments, described here. however, code i've got doesn't work - instead, plays 1 of parts.

i create augraph follows:

newaugraph (&_processinggraph); aunode samplernode, samplernodetwo, samplernodethree, ionode, mixernode;  audiocomponentdescription cd = {}; cd.componentmanufacturer     = kaudiounitmanufacturer_apple;  //---------------------------------------- // add 3 sampler unit nodes graph //---------------------------------------- cd.componenttype = kaudiounittype_musicdevice; cd.componentsubtype = kaudiounitsubtype_sampler;  augraphaddnode (self.processinggraph, &cd, &samplernode); augraphaddnode (self.processinggraph, &cd, &samplernodetwo); augraphaddnode (self.processinggraph, &cd, &samplernodethree);  //----------------------------------- // 2. add mixer unit node graph //----------------------------------- cd.componenttype          = kaudiounittype_mixer; cd.componentsubtype       = kaudiounitsubtype_multichannelmixer;  augraphaddnode (self.processinggraph, &cd, &mixernode);  //-------------------------------------- // 3. add output unit node graph //-------------------------------------- cd.componenttype = kaudiounittype_output; cd.componentsubtype = kaudiounitsubtype_remoteio;  // output speakers  augraphaddnode (self.processinggraph, &cd, &ionode);  //--------------- // open graph //--------------- augraphopen (self.processinggraph);  //----------------------------------------------------------- // obtain mixer unit instance corresponding node //----------------------------------------------------------- augraphnodeinfo (                              self.processinggraph,                              mixernode,                              null,                              &mixerunit                              );  //-------------------------------- // set bus count mixer //-------------------------------- uint32 numbuses = 3; audiounitsetproperty(mixerunit,                               kaudiounitproperty_elementcount,                               kaudiounitscope_input,                               0,                               &numbuses,                               sizeof(numbuses));    //------------------ // connect nodes //------------------  augraphconnectnodeinput (self.processinggraph, samplernode, 0, mixernode, 0); augraphconnectnodeinput (self.processinggraph, samplernodetwo, 0, mixernode, 1); augraphconnectnodeinput (self.processinggraph, samplernodethree, 0, mixernode, 2);  // connect mixer unit output unit augraphconnectnodeinput (self.processinggraph, mixernode, 0, ionode, 0);  // obtain references of audio units nodes augraphnodeinfo (self.processinggraph, samplernode, 0, &_samplerunit); augraphnodeinfo (self.processinggraph, samplernodetwo, 0, &_samplerunittwo); augraphnodeinfo (self.processinggraph, samplernodethree, 0, &_samplerunitthree); augraphnodeinfo (self.processinggraph, ionode, 0, &_iounit); 

i load 3 instruments soundfont (ids 0, 1 , 2 in soundfont) follows, passing in 'bankurl' of soundfont:

// load first instrument ausamplerbankpresetdata bpdata; bpdata.bankurl  = (__bridge cfurlref) bankurl; bpdata.bankmsb  = kausampler_defaultmelodicbankmsb; bpdata.banklsb  = kausampler_defaultbanklsb; bpdata.presetid = (uint8) 0;  audiounitsetproperty(self.samplerunit,                               kausamplerproperty_loadpresetfrombank,                               kaudiounitscope_global,                               0,                               &bpdata,                               sizeof(bpdata));  // load second instrument ausamplerbankpresetdata bpdatatwo; bpdatatwo.bankurl  = (__bridge cfurlref) bankurl; bpdatatwo.bankmsb  = kausampler_defaultmelodicbankmsb; bpdatatwo.banklsb  = kausampler_defaultbanklsb; bpdatatwo.presetid = (uint8) 1;  audiounitsetproperty(self.samplerunittwo,                               kausamplerproperty_loadpresetfrombank,                               kaudiounitscope_global,                               0,                               &bpdatatwo,                               sizeof(bpdatatwo));  // load third instrument ausamplerbankpresetdata bpdatathree; bpdatathree.bankurl  = (__bridge cfurlref) bankurl; bpdatathree.bankmsb  = kausampler_defaultmelodicbankmsb; bpdatathree.banklsb  = kausampler_defaultbanklsb; bpdatathree.presetid = (uint8) 2;  audiounitsetproperty(self.samplerunitthree,                               kausamplerproperty_loadpresetfrombank,                               kaudiounitscope_global,                               0,                               &bpdatathree,                               sizeof(bpdatathree)); 

finally, set ausampler nodes used each musictrack follows:

//------------------------------------------------- // set ausampler nodes used each track //------------------------------------------------- musictrack track, tracktwo, trackthree; musicsequencegetindtrack(testsequence, 0, &track); musicsequencegetindtrack(testsequence, 1, &tracktwo); musicsequencegetindtrack(testsequence, 2, &trackthree);  aunode samplernode, samplernodetwo, samplernodethree; augraphgetindnode (self.processinggraph, 0, &samplernode); augraphgetindnode (self.processinggraph, 1, &samplernodetwo); augraphgetindnode (self.processinggraph, 2, &samplernodethree);  musictracksetdestnode(track, samplernode); musictracksetdestnode(tracktwo, samplernodetwo); musictracksetdestnode(trackthree, samplernodethree); 

however, when play musicplayer, hear single part playing. problem arising in trying use different instruments - when use single instrument standard musicplayer setup (instead of editing augraph above), works fine.

does have idea i'm doing wrong?

i've found solution. before loading instruments soundfont, following line needed:

musicsequencesetaugraph(testsequence, self.processinggraph); 

as long point @ line run comes before instruments loaded soundfont , before various musictracks assigned ausampler nodes, seems work - parts played on different instruments, desired. this answer related question helped me figure out.