I am currently listening to a collection of Bach's complete organ works for the organ. I love Baroque music and Bach in particular, but I am not very familiar with the organ from the performer's perspective (I play the piano). I know that the organ console has sets of "stops" which are used to activate sections of pipes which may have the same pitch, but different sound characteristics, but that's about it.
Anyway, while listening to the music, I noticed some of the works sounding radically different from that dictinct, powerful organ sound. Some of them sound kind of squeaky, the bass and lower treble just a distant, nasal hum. I was wondering if it could be recorded on a different instrument, or were just different stops activated? If so, is the usage of those regulated in the notation, or is the performer supposed to excercise their own discretion? I suppose that since the organ doesn't have a dynamic keyboard, the performer has to use some other means of obtaining different sound dynamics, are these the employment of stops?