Sound archives are essential in adding sound design to your mix. Here are some good examples of places to find free (and good!) sound: 

BBC Sound Effect Archive

Envato Elements

Free Music Archive

Free Sound

Incompetech

Internet Archive 

• Audio Archive
• Folsoundomy: Sound Effects and Recorded Ambiance
• Music, Arts & Culture

Melody Loops

Premium Beat

SoundBible.com

Further Resources:

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