What are some ideas for a music-based birthday cake?

A cake topper that hides a tiny mp3 player in it.

Or buy one of those music cards and cut out the music playing part, then have one of the cake toppers become the trigger to play the music.

Or get one of those little push-button, it sings toys and use that as a cake topper.

If you’re talking about cake decoration ideas, can’t go wrong with music notes.

http://www.coolest-birthday-cakes.com/party-cakes.html

Shaped like a music note?
Put some lyrics on it?
The name of his/her favorite song, or band?

Decorate the cake to look like a piano, guitar or a scene from a concert with the band in one corner and all the fans covering the rest of the cake.

You can get a container of decorative frosting with a piping nozzle available in many colors. Frost the cake as smoothly as your can. Pipe 5 evenly spaced straight lines across the cake. Pipe a treble clef sign on the left end of the lines. Write Happy Birthday in cursive across the lines. That’s the easiest I can think of.

These
Are
Super
Cool
Ideas.

Make a long sheet cake and decorate it in a circus atmosphere. In the middle of the cake, center a Jack in the Box. At the birthday party. make a wish and play the song and wait for Jack to present himself with a small note that says, “Happy Birthday”.

Eeeeeasy. White sheet cake. Buy black writing icing and draw a treble clef and five lines. Use M&Ms for the circle part of the notes, and the icing for the stems. It’ll look great!

Make a layer cake. Draw lines around it that look like a staff. Place musical notes on it.

Music notes shaped in chocolate, marzipan or merengue. You can decorate the notes with edible gold dust too, it comes in a bunch of colors.

if you want to make music notes, you could just look for cookie cutters in the shape of one, roll out some coloured fondant icing (I think it’s easiest to find that in the UK and USA, or just order it online) and just cut out the shapes… :)