A free app for Android, by palcoder.

Smart Audio Effects & Filters is a free audio effects editing app. You can apply various filters and effects on sound or a full blown song, such as Echo, Delay, Speed, Fade in/Fade out, Bass, Pitch, Treble, Chorus, Flanger, Earwax sound effect, and many more. It also has a powerful equalizer with bass, treble, mid, and high frequencies. You can also use this app to trim audio files and make your own ringtone.

It is a very simple app with a user-friendly interface. You can use it with or without learning C++ programming. It also works on Android 4.2 and above.