Sorry for the clickbait title. I promise this post delivers: 44100 Hz stereo with near-Opus bitrates using about 4% of the N64’s CPU time.
But first, some history: The options for playing and storing audio data on the N64 were dire. The PlayStation could just stream uncompressed redbook audio straight from the CD. On the N64, cartridge space was at a premium and time on the 93 MHz CPU was limited.
Worse, access to the vector co-processor, the RSP, was guarded by Nintendo for the longest time. Nintendo's own platform library, Libultra, internally used the RSP for various graphics and sound-related tasks, but Nintendo didn't allow third-party developers to directly write code for it.
Libultra provided some functions to transparently play back compressed audio using an ADPCM scheme (adaptive differential pulse code modulation). The RSP handled decompression on the fly, just before the audio was sent to the output buffer.
