I need to slow down speech files (audiobooks) at around 80 percent of the original speed. Please advice a good audio editor that you know can do the job without loosing the pitch, or that it can compensate for it. Major packages ok. Need not to be a specialized one.

Thanks for the help

Audacity will do what you require.

It's freeware and will allow you to slow down any audio file without changing the pitch.

Once installed, open the file and click 'Edit > Select > All'. While it is highlighted click 'Effect > Change Tempo' and try out different settings by using the 'Preview' button on the Change Tempo panel.