chn_setvolume_matrix
ret |= chn_setvolume_matrix(c, vc, i, left);
ret |= chn_setvolume_matrix(c, vc, i, right) << 8;
ret |= chn_setvolume_matrix(c, vc, i, center) << 16;
chn_setvolume_matrix(c, SND_VOL_C_PCM, SND_CHN_T_VOL_0DB, db);
chn_setvolume_matrix(c, vc, i, c->volume[vc][SND_CHN_T_VOL_0DB]);
int chn_setvolume_matrix(struct pcm_channel *c, int vc, int vt, int val);