If you’re just a beginner, There’s a free music school called Siddartha, at ቀጨኔ around Medhanialem. They’re really good even for advanced musicians. You’ll learn jazz and every other rhythms. But if you have some musical background you can take entrance exam and enroll at Jazz Amba, around Piassa Taytu hotel, for almost free price. If you’re rich enough and want a full time music class, go to Seminary Music School around Mekanisa.