snd_opl3_calc_volume
snd_opl3_calc_volume(®_val, vel, chan);
snd_opl3_calc_volume(&vol_op[3], vel, chan);
snd_opl3_calc_volume(&vol_op[2], vel, chan);
snd_opl3_calc_volume(&vol_op[0], vel, chan);
snd_opl3_calc_volume(&vol_op[1], vel, chan);
snd_opl3_calc_volume(&vol_op[1], vel, chan);
snd_opl3_calc_volume(&vol_op[0], vel, chan);
void snd_opl3_calc_volume(unsigned char *reg, int vel, struct snd_midi_channel *chan);