Part 3 of the translated "Iwata Asks" interviews with the Super Mario Galaxy team is up, and this part's theme is the game's music and sound engineering.

Notable quotes:

Koji Kondo, on why Nintendo rarely uses orchestrated musicIt almost seems like while you're playing the game, the music is coming from a CD player, and not from the game console and it feels like you are obligated to play the game in time to the music. For that reason, Nintendo has only used a live orchestral soundtrack on a few occasions in the past.

Masafumi Kawamara, on the process of precisely mixing sound with streamed music...the game synchronises MIDI data with the streaming data, and this is used to process the sound effects at the right time. When Mario shoots off from the Sling Star, for example, harp music plays as a sound effect. If you listen carefully, this harp will sound in perfect timing with the background music. This kind of technique rarely gets noticed however.

Mahito Yokota, on making the music's tempo fit the gameMusic from the orchestra will play at the tempo that had been set in the studio, which usually is just a little off from the tempo of Mario running. I absolutely wanted to avoid using music that simply played regardless of the game's tempo, so I got this device that works in a similar way to a metronome, where it would tick at the exact tempo with the game. I asked the orchestra, "Please perform at exactly the same rhythm as this."

Iwata Asks: Super Mario Galaxy - Volume 3