Our second entry in the timeline comes from Nintendo's Tetris for the GameBoy. This song was created in 1989, and was composed by Hirokazu Tanaka in Japan. (3) While the other themes in Tetris are based on famous classical Russian orchestral pieces, this is the first original song composed for this game.
This song premieres on a handheld console, and as such has lower sound capacity when compared to stationary home consoles of its time. And while no true instruments can be heard -- 'beeps' and 'boops' are still only tone being created -- the slightly higher complexity of the piece is evident.
The first few measure of the song's sheet music seen here elaborates on that complexity. While DigDug had only two melodies playing at once, Tetris improves upon that slightly by having three simultaneous rhythms playing at once, two of which being the main melody and one providing a bass line.
A debut mechanic in the timeline is seen here with the GameBoy: the use of a 'noise-wave'. This can be heard as the faint drum-like sounds in the background of the track.