Change mp3 bitrate

Hi, how can change the mp3 bitrate, from 128 to 64 or 96 on airtime 1.70 o 1.6.1?



I tried to change the file ls_script.liq on airtime 1.6.1 with this new line

""
if output_icecast_mp3 then
out_mp3 = output.icecast(%mp3,
host = icecast_host, port = icecast_port,
password = icecast_pass, mount = mount_point_mp3,
fallible = true,
bitrate = 96,
restart = true,
restart_delay = 5,
url = icecast_url,
description = icecast_description,
genre = icecast_genre,


but the output was always at 128

how can I do? thanks and sorry for the trouble!