#!/bin/sh
# Script to compare my original mp3s to the new 'matched' versions
# Copyright © 2012 W Tristan Collins - All Rights Reserved
# Do what the hell you like with this.
SAVEIFS=$IFS # save the old IFS variable
IFS=$'\n\b' # change IFS to cope with spaces in paths/filenames
oldFILES=source/* # directory of old mp3s
newFILES='/Users/Tristan/Music/iTunes/iTunes Music/*' # iTunes music directory
extension='.mp3' # set the extension we are looking for, in this case mp3
# prepare output file
echo Name,Old Dynamic Compression,New Dynamic Compression > out.csv
echo Name Old New
for file in $oldFILES # for each of the original mp3s
do
oldNAME=`basename $file $extension` # strip the path and extension
newNAMEarray=(`find $newFILES -name $oldNAME\*`) # find the corresponding new file
for i in ${newNAMEarray[*]}
do
# echo "$i" # this is where the comparison could be done
# This is a measure of Dynamic Range Compression
# using [url=http://www.pitchtech.ch/DRC-Meter/index.html]http://www.pitchtech.ch/DRC-Meter/index.html[/url]
# Smaller numbers are better (less obvious compression used)
procold=$(java -jar DRC-Meter/DRC-Meter.jar "$file" | tail -c 5)
procnew=$(java -jar DRC-Meter/DRC-Meter.jar "$i" | tail -c 5)
echo $oldNAME $procold $procnew
echo $oldNAME,$procold,$procnew >> out.csv
done
done
IFS=$SAVEIFS
exit 0

As far as DRC is concerned (and I am aware of the issues measuring this - I am no expert), and without bother to do any complex statistics (just don't have the time), the output indicates that "the 'new' versions supplied by iTunes Match have slightly more DRC (more compressed) than the originals. But this is only slight. The vast, vast majority of the new files are practically identical. There are a few outliers where there are big differences indicating potentially differing sources.

Anyway, I'm happy with iTunes Match.

Just checking: did you verify the results of your script with your ears?

If the file is in Apple's catalogue, you get whatever version they have through Match. This version does not need to have come from the same master source as your file, so differences to your files are very much expected. This is not a backup solution, but rather an option to access your files from anywhere, just like Google Music offers, too. Or, for the more illegal crowd, an opportunity to launder pirated music through Apple.
So, the generalization that ""the 'new' versions supplied by iTunes Match have slightly more DRC" is invalid, since the opposite is just as likely. That said the "Mastered for iTunes" program has some traction among known horrible engineers, which could very likely result in a higher abundance of highly DRCd tracks on iTunes.

That's the most important point. If you fear though that iTunes Match doesn't deliver the quality you have on your CDs, you should probably keep a separate rip of those just in case.