Here's a shell approach. It will delete any directories that don't contain .mp3 files of the >= 320 kbps bitrate:

find /path/to/Music -type d -print0 | 

    while IFS= read -r -d '' dir; do 

     mp3=$(find "$dir" -type f -iname '*.mp3' | head -n 1); 

     [ -e "$mp3" ] && [[ $(mp3info -x "$mp3" | grep -oP 'd+(?=s*kbps)') -lt 320 ]] && 

            rm -rf "$(dirname "$mp3")"; 

    done

Notes

• This will remove any directories that contain at least one mp3 file with a bitrate less than 320. If another file exists in the same directory with the right bitrate, that will be deleted as well. This approach assumes that all files in a directory have the same bitrate.

  
  



• This will miss files of variable bitrate.

  
  



• It should work with any type of file name, including those with spaces, newlines or even backslashes.

  
  



• You might need to install mp3info: sudo apt-get install mp3info

  
  



• Run it on a test directory first.

  
  

Explanation

• find /path/to/Music -type d -print0 : find all directories under /path/to/Music and print them separated by the null string. This is needed to deal with strange file names.

  
  



• while IFS= read -r -d '' dir; do : go through each of the results of find, saving them in the $dir variable.

  
  



• mp3=$(find "$dir" -type f -iname '*.mp3' | head -n 1); : save the name of the first mp3 file in this directory as $mp3.

  
  



• [ -e "$mp3" ] : if this file exists. This is needed for skipping directories with no mp3 files.

  
  



• [[ $(mp3info -x "$mp3" | grep -oP 'd+(?=s*kbps)') -lt 320 ]] : this checks the bitrate of $mp3. It runs mp3info, greps the bitrate and checks if it is less than 320.

  
  



• rm -rf "$(dirname "$mp3")"; : delete the directory that contains the mp3 file. This will only be run if its bitrate is less than desired.