The new DAC's are made by Cirrus. This link has lots of graphs and discusses the sound differences, and includes several links to the topic at the bottom:
http://homepage.mac.com/marc.heijligers/audio/ipod/comparison/measurements/measurements.html
So far, my favorite sounding Ipod was the original shuffle.
http://homepage.mac.com/marc.heijligers/audio/ipod/comparison/measurements/measurements.html
So far, my favorite sounding Ipod was the original shuffle.