The difference is the use of perfective and imperfective forms. If you use two perfective verbs (Alberto OYÓ la música y SALIÓ de casa) you are describing a sequence of actions. One thing happened after another. If you use an imperfective form and a perfective one (Alberto OÍA la música cuando SALIÓ de casa) the imperfective verbs sets the scenario of what was happening when something else (the perfective form) took place. Esta mañana lavé la ropa y saqué a pasear al perro. ("lavé", perfective form of "lavar" and "saqué" perfective form of "sacar"). This morning I did the laundry and I walked the dog. Casandra veía televisión cuando llegué a casa. ("veía" imperfective of "ver" and "llegué" perfective of "llegar). Casandra was watching TV when I got home. You can find a more detailed explanation and examples if you read the following article: https://mgvillarroel.wordpress.com/2014/07/23/perfective-and-imperfective/ I hope that helps.

Right Alberto's response is correct A literal translation to English, would be: "Alberto heard the music from the party and left home" and "Alberto was hearing the music from the party when he left home"

"Alberto oyó la música de la fiesta y salió de casa": es una acción pasada que ya terminó. "Alberto oía la música de la fiesta cuando salió de casa": es una acción pasada que no está terminada.

I would say that in the first one, it's a sequence of events, first Alberto listens to the music then he leaves the house. In second one, both things are happening at the same time.