While sheet music will give you the full melody of a song, there is always the instrumental or Contra Melodies that may be in the song
and are not always included in the sheet music, so one of the ways to figure them out is by ear. This can be a long laborious task
so heres a little app that is basically free that will allow you to slow down the tempo of any audio file while still retaining the original pitch
Which will make your practicing of the instrumental or Contra Melodies adlib bits a little easier.

The basic app is free, but there are additional add ons that can be purchased if required, like transpose etc.
Please be aware that this app has received mixed reviews and I havent tried it myself personally




https://itunes.apple.com/us/app/tempo-slowmo-bpm-music-practice/id460008289?mt=8&ign-mpt=uo%3D4

Brian007