Slow down whole project

Hi.

i want to be able to temporarily slow down the whole project while editing so I can hear all the MIDI and audio as normal but in slow motion.

if I slow the tempo of the project the audio regions get dramatically smaller in length and the midi regions stay the same size. So essentially the audio sounds exactly the same time not slow motion.

Is there any way of slowing the project but keeping regions the same size.

Any help greatly appreciated.

Hope this makes sense

Thanks

Keith