Amy X. Wang for Rolling Stone:

In the first media visit Apple has ever allowed to its under-the-radar Music Apps studio, the team of engineers showed Rolling Stone how the creation process for Garageband's two types of sounds – synthetic and "real" – can span weeks or sometimes months per instrument, with new hurdles at every turn. Synthesized sounds (i.e. the type of obviously artificial notes often heard in EDM) are made from code and tweaked by code; "real" sounds have to be recorded in a drop-dead-silent studio setting, dozens of times, then pieced together like patchwork to form single perfect notes, one by one.

Some instruments are extra excruciating. In the digital reproduction of an American upright bass, a player in the studio plucks a string, holds his breath for seven seconds to ensure there's no extra noise on the recording whatsoever as the note shivers into the air (engineers have custom-coded an app to time the duration precisely), and repeats the endeavor at different finger positions, volumes and pressures, day in and day out. After wheeling each of the cavalcade of instruments out of the studio, the team pores over the hundreds of recordings to pick out the best. When adding a suite of East Asian instruments in a recent product update, the engineers consulted with designers across the world to pick out the specific color of wood and font of a poem that would make a Chinese guzheng appear the most authentic. Engineers also constantly browse music-making forums for complaints, suggestions and thoughts on what to tweak next.

It's truly amazing that Apple spends so much time and effort on a free app.