Walking Player offers standard OS Music Player library.(AVAudioPlayer)The adjust the tempo using the playback speed adjustment function, but not so good quality for Tempo adjustment after depending on the song. Song especially in the Ballad of vibrato highly seasoned stand deterioration. Song of the drum reverse beats clearly the less noticeable degradation.

If the sound quality comes to mind "Player screen"The let us Skip play mode, tap the playback mode display. Skip play mode will skip play specified tempo range if the original tempo and the original tempo tempo range of songs only play at the original playback speed. For this reason, sound quality without, you can play only songs in the specified tempo range.

I think better for playback sound quality about the sound quality of the playback rate coordination, future research, and more comfortable.