Okay, so tonal memory is when you remember a sound in your head without actually hearing it at the moment. Just like how you remember a picture in your head, tonal memory is when you remember a sound.
For example, if you hear a song on the radio and then later on you start humming the tune of the song without actually listening to it, that's tonal memory. Your brain remembers the sound and you can replay it in your head even if you're not hearing it out loud.
It's like when you remember your mom's voice saying, "Time to brush your teeth!" even when she isn't there telling you to do it. That's your tonal memory at work!