If you install lame and mp3info into your Mint (or Debian) Linux box, the following code will help you downsample your music collection from one directory to another.

#!/bin/bash

  INPUT_DIR="/data/PhoneMusic1"
 OUTPUT_DIR="/data/downsampled"
ARCHIVE_DIR="/data/OriginalMusicArchive"
NEW_BITRATE=128
SAVINGS=0

IFS=$'*'

cd ${INPUT_DIR}

for ALBUM in *
do

  if [ "${ALBUM}" != "$0" ]
  then

    ORIGINAL_SIZE=$(du -sch ${INPUT_DIR}/${ALBUM} | grep total | awk -F'M' '{print $1}')

    cd    "${INPUT_DIR}/${ALBUM}"
    pwd

    if ! [ -d "${OUTPUT_DIR}/${ALBUM}" ]
    then

      mkdir "${OUTPUT_DIR}/${ALBUM}"

    fi

    for TRACK in *.mp3
    do

      if ! [ -f "${OUTPUT_DIR}/${ALBUM}/${TRACK}" ]
      then

        OLD_BITRATE=$(mp3info -r a -p "%f %r\n" ${TRACK} | awk '{print $NF}'| awk -F'.' '{print $1}')

        if [ ${OLD_BITRATE} -gt ${NEW_BITRATE} ]
        then

          echo "Downsampling ${OLD_BITRATE}->${NEW_BITRATE}: Track: ${TRACK}"
          lame --mp3input -b ${NEW_BITRATE} -q0 "${TRACK}" "/tmp/${TRACK}" > /dev/null 2>&1
          mv "/tmp/${TRACK}" "${OUTPUT_DIR}/${ALBUM}"

        else

          echo "Low Sample Rate: ${OLD_BITRATE}, ${OUTPUT_DIR}/${ALBUM}/${TRACK}"
          cp "${TRACK}" "${OUTPUT_DIR}/${ALBUM}/${TRACK}"

        fi

      else

        echo "Previously Converted: ${OUTPUT_DIR}/${ALBUM}/${TRACK}"

      fi

    done

    NEW_SIZE=$(du -sch ${OUTPUT_DIR}/${ALBUM} | grep total | awk -F'M' '{print $1}')
    DELTA=$((${ORIGINAL_SIZE}-${NEW_SIZE}))
    SAVINGS=$((${SAVINGS}+${DELTA}))

    echo "Original Size: ${ORIGINAL_SIZE}M, New Size: ${NEW_SIZE}M, Delta: ${DELTA}M & Savings: ${SAVINGS}M"

    cd "${INPUT_DIR}"
    mv "${ALBUM}" "${ARCHIVE_DIR}"

  fi

done