After you have found music and sound effects for your sound design, you will want to make sure they are just right. Sometimes a song starts at the wrong place or gets too loud at a certain point. Sometimes you need to loop a sound or add an effect to it.
Although my digital audio workstation of choice is Ableton Live, Garageband is free and comes preloaded on most Macs, so I will be using it for demonstration. It has many features, but I will only cover the ones most necessary for basic sound design. For a more detailed tutorial, check out Udemytutorials or Macworld. Below is the basic Garageband workstation.
You will first want to drag whichever sound file you wish to edit to the track labelled Audio 1. From here, you can control its volume, adjust its length, and add effects.
First, we will adjust the length of a sound effect. I made a sound effect of a scream, followed by a gunshot, and I want to cut out the scream. To do this, I will drag from the top left of the sound file (circled in red) to the beginning of the gunshot so that only the second sound plays.
Second, we will adjust the volume. I wanted my sound effect of dogs growling to fade out slowly after 5 seconds, so I clicked the fader button (circled in red) and clicked the yellow volume line to create three points (also circled). I then dragged the second two down to created a gradual fade out effect.
Next, we will loop a sound effect. This can be useful if a sound needs to be playing throughout an entire scene. I am going to loop a sound effect of waves splashing. The sound effect starts with one loud splash that I only want at the beginning, however, so we will need to skip that for subsequent loops. I created a new track, and used my volume sliders to make the audio switch between the two tracks on a loop.
Finally, we will add an effect. I want my gunshot to sound like it is coming from far away, so I am going to add reverb to it. To do this, I hit the mixer button (circled in red) and adjusted the reverb knob. Perfect!
Feel free to ask questions in the comment section, and make sure to follow Staging Sounds for more information about theatrical sound design!