let mut acb_vec = [0; SUBFRAME_LEN];
let mut tmp = [0; SUBFRAME_LEN * 2];
for i in (0..SUBFRAMES).step_by(2) {
let buf = &mut self.synth_buf[LPC_ORDER + SUBFRAME_LEN * i..];
self.subframe[i].gen_acb_excitation(&mut acb_vec, buf, self.is_6300);
let mut acb_vec = [0; SUBFRAME_LEN];
let mut tmp = [0; SUBFRAME_LEN * 2];
for i in (0..SUBFRAMES).step_by(2) {
let buf = &mut self.synth_buf[LPC_ORDER + SUBFRAME_LEN * i..];
self.subframe[i].gen_acb_excitation(&mut acb_vec, buf, self.is_6300);