#!/bin/sh
find ./ -type f -iname "*.mp3" -printf "%p\n" | while read f
do
    fname="${f%.mp3}"
    sox -S "$f" -c 1 -r 16000 "$fname.wav" gain -n -3;
    ./fdkaac -p 2 -b 11 -m 0 --transport-format 2 "$fname.wav" -o "$fname.m4a";
    rm -f "$fname.wav";
    rm -f "$fname.mp3";
done