[devote]

var MusicArray = {
 "0":[123, 133, 1, 21231233123, 1323,213323,1231],
 "1":[321,231, 33, 2123,12323,21323,123323],
 "2":[223,211, 95, 213123,1223,2213,13223],
 "3":[233,223, 7, 213123,11223,23123,132123],
 length: 4
}

Array.prototype.sort.call( MusicArray, function( a, b ) {
    return a[2] > b[2] ? 1 : a[2] < b[2] ? -1 : 0;
});

alert( JSON.stringify( MusicArray ) );