Adding an audio track is relatively easy in PS. The key is making sure you have the right audio format. For some reason, .mp3 files are troublesome, so it is best to work with .wav files. I would also suggest working with Adobe’s Audition if you are wanting to edit a file together.
This is an example of two different files in Audition. You can see that that sample rates (Hz numbers) are different but their bit depth matches at 24. PS likes audio files that are in the wave format with a sample rate of 48000 Hz and a bit depth of 24.
It is easy to convert the file to the needed requirements. Go to the Edit Menu and choose Convert Sample Type. This then brings up another window where you choose the settings you want.
When you have it converted to what you want, then do a Save As and choose .wav. You will then be able to easily add your audio track to PS.