Noise reduction will remove noise from your signal. Your audio file can be a voice over or mixed song. Most recording devices (analog or digital) have self noise that can use reducing. The better the hardware, the less noise usually needs to be removed. The noise can be random or white noise. White noise is a random signal with a constant power spectral density. Electronically recorded music usually have a hiss influenced by the voltage of the output signal.
Run audio through noise reduction toolsAutomation on top of compression for extra consistencyEQ to add clarity