fx_twice_value
#define fx_lfo1_freq fx_twice_value /* [0,127] 84mHz */
#define fx_lfo1_volume fx_twice_value /* [0,127] 0.1875dB */
#define fx_lfo1_cutoff fx_twice_value /* [-64,63] 56.25cents */
#define fx_lfo2_freq fx_twice_value /* [0,127] 84mHz */
#define fx_cutoff fx_twice_value /* [0,127] 62Hz */
static int fx_twice_value(int val);