On my Core2Duo E6850 3GHz, Windows 7 Profellional 64bit, I only have 25% CPU usage when re-compressing MP3 files. When I assign only one core to the CDEx process in Windows task manager, the process runs 100% on that core, i.e. 50% in total.
This are my compression settings:
CDEx 1.70 beta 4, Lame 1.32 engine 3.98
Converting to MP3 64kbit/s CPR, stereo (from 128 kbit/s source)
Output sample rate 44100 kbit/s
Thread priority normal