iOS sound fader for AvAudioPlayer written in Swift

This is an iOS utility class that allows to fade sounds in and out with AvAudioPlayer. One can set duration and velocity of the fade. Velocity can vary from linear to logarithmic.

Installation

Copy iiFaderForAvAudioPlayer.swift file to your project.

Usage

Play an audio file

import AVFoundation

let soundURL = CFBundleCopyResourceURL(CFBundleGetMainBundle(), "my_lovely_horse.mp3", nil, nil)
let player = AVAudioPlayer(contentsOfURL: soundURL, error: nil)
player.play()
player.volume = 0

Instantiate a fader

let fader = iiFaderForAvAudioPlayer(player: player)
fader.fadeIn()
fader.fadeOut()

I would create a fader property somewhere in my app and keep a strong reference to the fader.

Set fade duration and velocity

fader.fadeIn(duration: 3, velocity: 2)

Supply fade start/end volume, completion callback

fader.fade(fromVolume: 0.3, toVolume: 0.7, duration: 3, velocity: 2) { finished in
  // fading finished
}

Set the quality of fade

fader.volumeAlterationsPerSecond = 20

Larger numbers will produce finer fade effect at expense of CPU juice.

Volume functions

The following graph shows how sound volume changes during the fade.

Fade in formula

Fade out formula

Where x is time and v is velocity.

Velocity of 0 creates a linear fade. Values greater than zero produce more logarithmic fade affect. Logarithmic fade sounds more gradual to a human ear. I personally use velocity values from 2 to 5.

Live graph demo: https://www.desmos.com/calculator/wnstesdf0h

Demo app

Attribution

The lovely music was recorded by Carlos Vallejo and downloaded from http://www.flashkit.com/loops/Easy_Listening/Ill_Be_-Carlos_V-10012/index.php

Project home

https://github.com/evgenyneu/sound-fader-ios