The phenomenon you're describing is often referred to as "hearing" or "auditory imagination," where you can mentally recreate or recall sounds, such as a favorite song, without any external sound waves actually entering your ears. While it may seem like you are "hearing" the sound inside your head, the experience is not based on the physical transmission or reception of sound waves.
The ability to internally "hear" sounds is a product of our brain's capacity to generate mental representations and simulate auditory experiences. When we listen to music or any other sound, our brain processes the auditory information and stores it in memory. We can then recall and reconstruct these stored memories, including the sounds associated with them, without the need for actual sound waves.
The process of mentally "hearing" a song or sound in your head involves activating neural circuits in the auditory cortex of your brain. These neural circuits simulate the patterns of neuronal activity that would typically occur when you hear the sound externally. It's a form of mental imagery or cognitive processing that recreates the perception of sound.
While the experience of hearing sounds in your head can be vivid and detailed, it is important to note that it is a subjective internal experience rather than an external auditory sensation. It relies on the brain's ability to recall and simulate auditory information, and it does not involve the physical transmission or reception of sound waves.