if [ "$#" -ne 5 ]; then
    echo "Usage: $0 <in.wav> <out.wav> <rate_min> <rate_step> <rate_max>"
    exit
fi

FN_IN=$1
FN_OUT=$2
RATE=$3
STEP=$4
MAX=$5

ITER=0
while true; do
  if (( $(echo "$RATE > $MAX" | bc -l) )); then
    break
  fi
  let ITER+=1
  RATE=`echo "$RATE+$STEP" | bc`
  sox $FN_IN "tmp_$ITER.wav" speed $RATE
done

sox tmp_* $FN_OUT
rm tmp_*