#!/bin/bash

cd /pub/multimedia/audio/music/by-artist
for ARTIST_DIR in */; do
    echo -n "$ARTIST_DIR ..."
    MAX_TS=$(find "$ARTIST_DIR" -maxdepth 1 -mindepth 1 -exec stat -c %Y {} \; | sort -rn | head -1)
    touch -t $(date -d@$MAX_TS +%Y%m%d%H%M.%S) "$ARTIST_DIR"
    echo
done