You can create the audio file in an editor such as Audacity or Free Audio Editor. Both are linked in SeeMyWorld. PD does not have any advanced audio editing, but you actually put your music in the timelines, create an A/V file, then rip the sound from that file in the library. HP Envy Phoenix/4thGen i7-4770(4@3.4GHz~turbo>3.9)
Nvidia GTX 960(4GB)/16GB DDR3/
Canon Vixia HV30/HF-M40/HF-M41/HF-G20/Olympus E-PL5.
Tape capture using 6 VCR, TBC-1000, Elite BVP4+, Sony D8 camcorder with TBC.
https://www.facebook.com/BarryAFTT

Quote: but you actually put your music in the timelines, create an A/V file, then rip the sound from that file in the library.

Thanks for the quick reply. What do you mean by ripping the file in the library?

Place music in timeline.
Create file. (this will create an A/V file, even though the video is empty).
The new file will automatically go into your library.
Right-click the file.
There should be an option to extract the audio.
This will create an audio file from the soundtrack of the A/V you created.
You can then add that to your slideshow.

Note: When you create your A/V, any type will do, it's the audio you're chasing after. HP Envy Phoenix/4thGen i7-4770(4@3.4GHz~turbo>3.9)
Nvidia GTX 960(4GB)/16GB DDR3/
Canon Vixia HV30/HF-M40/HF-M41/HF-G20/Olympus E-PL5.
Tape capture using 6 VCR, TBC-1000, Elite BVP4+, Sony D8 camcorder with TBC.
https://www.facebook.com/BarryAFTT

Thank you very much Barry. No, I am not a member but I will check it out.