func toBytes(l, r []int16) []byte {
	if len(l) != len(r) {
		panic("len(l) must equal to len(r)")
	}
	b := make([]byte, len(l)*4)
	for i := range l {
		b[4*i] = byte(l[i])
		b[4*i+1] = byte(l[i] >> 8)
		b[4*i+2] = byte(r[i])
		b[4*i+3] = byte(r[i] >> 8)
	}
	return b
}
func toBytes(l, r []int16) []byte {
	if len(l) != len(r) {
		panic("len(l) must equal to len(r)")
	}
	b := make([]byte, len(l)*4)
	for i := range l {
		b[4*i] = byte(l[i])
		b[4*i+1] = byte(l[i] >> 8)
		b[4*i+2] = byte(r[i])
		b[4*i+3] = byte(r[i] >> 8)
	}
	return b
}
// toBytes returns the 2ch little endian 16bit byte sequence with the given left/right sequence.