+ {
+ /* map each context (voice) to its own channel */
+ Context *c = inf.origin_contexts (this)[0];
+ string id = c->id_string ();
+ int channel = channel_map_.size ();
+ /* MIDI players tend to ignore instrument settings on channel
+ 10, the percussion channel. */
+ if (channel % 16 == 9)
+ channel_map_[""] = channel++;
+
+ map<string, int>::const_iterator i = channel_map_.find (id);
+ if (i != channel_map_.end ())
+ channel = i->second;
+ else
+ {
+ channel_map_[id] = channel;
+ if (channel)
+ set_instrument (channel);
+ }
+
+ ai->channel_ = channel;
+ audio_staff_->add_audio_item (ai);
+ }