|CD's use uncompressed pulse code modulation data, DVD's use a compressed mpeg format so there may be differences in the decoders used to play them. |
I would suspect however, that what you are hearing is a difference in audio material and audio compression. Most audio engineers today seem to love to compress the crap out of music so you can really crank up your stereo and perceive the sound to be louder. It also makes CD's sound better on smaller audio systems and portable players as well as mp3 players using headphones. DVD audio discs are tailored more for high end systems that can handle the wide dynamic range and are usually mastered with less compression than CD's. The more compression used, less difference between the quite and loud parts of the song. Movies on the other hand are very dynamic. Background music and speech is more subdued and the audio effects are usually quite loud.