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Adding Audio Clips

ScriptableObjects for audio can be created by "Right Clicking anywhere in the project panel > Create > Sound" or duplicating an already created SO.
ScriptableObjects will all have specific settings that control the audio clip which is used, that you can change, the volume, pitch, variance and whether it can loop. All features of the default "AudioSource" component.
In the "AudioManager" is good to add the size of the "Sounds" array to the number of sounds which will play within this system. By default it has 8 SO audio clips, these should be added to access them all.
In the "PLController" - Look at the inspector and you'll see slots for each of the applicable SO which you create in the project panel, add any of these to the appropriate slots. This allows you to play that specific SO from the audio manager.
Refencing the Audio Manager Use the code, within your scripts to reference your sounds to play
PLAudioManager.instance.Play(VariableSound.name);