Piano Forum

Good question! I think the answer is - it depends, but I'd say no.

The voice leading rule is at it's core about not having paralells between independent voices. The octaves in these transcriptions can be considered the representation of one independent voice (the added octave is a color to imitate the big sound of the pedals, rather than an independent vocie) so they do not break the rule. On the organ, you can pull out stops that make the actual sound produced when pressing one key be doubled with an octave. This was available to Bach, and yet doing this doesn't break any rules because each independent voice still follows the proper voice leading rules, even if some of them happen to be doubled in octaves by the configuration of the organ.

Consider the following example to see what I mean:



There is an error in voice leading here, but its not the octaves, assuming you consider them one voice that is colored, but rather between the octaves and another voice. Can you spot it?

When it comes to Bach, as far as I know he never wrote out any voices doubled in octaves in his keyboard compositions. I'm not familiar enough with his multi-instrumental music to know if he ever doubled certain voices with different instruments. In his keyboard music, whenever there are multiple notes sounding at the same times, such as a sequence of chords or what have you, he always treats each note as an individual voice that gets treated accordingly with correct voice leading.

It's funny, because the French baroque composer Rameau did use paralell octaves sometimes in his harpsichord music and he basically writes that he does it "because it sounds good bro".