Harman International, parent company of JBL, Lexicon, Digitech, AKG, Soundcraft, Crown, BSS Audio, and more fine brands, is offering a great, free opportunity for you to improve your critical listening skills. A free, beta version of their How to Listen software is available for download.
The software supports stereo and multi-channel audio playback of WAV files and provides a variety of training exercises where different kinds of timbral, spatial, and dynamic distortions are added to music — simulating situations often encountered in recording and audio playback chains. As you work your way through the exercises, the software automatically adjusts the difficulty of successive exercises based on your performance.
Both Mac and Windows platforms are supported.