1. https://www.videvo.net/royalty-free-sound-effects/ 2. https://www.motionelements.com/es/free/sound-effects 3. https://www.epidemicsound.com/es/sound-effects/ 4. https://www.freemusicprojects.com/es/41-efectos-de-sonido-gratis 5. https://www.themotionmonkey.co.uk/free-resources/retro-arcade-sounds