I don’t know much about musical notes… In programs like Audacity you can change a song’s speed by a percentage. When you don’t change it enough for the musical notes to change a semitone or a tone, is the resulting music lower audio quality in any way?
In other words, is there something special about the specific frequencies of the A-G# musical notes… such that if I increase the speed of a song by only 1% it will sound lower quality in some way?
Also: in the pitch change dialog, it tells me that a -10.910% change will take a note one step down. Does that apply to speed changes too? So if I reduce the speed of a song by -10.910%, any B will become an A etc…?
Some people have “perfect pitch”. What that means is that they are so accustomed to standard A440 tuning that they can recognise precisely what note is being played with reference to nothing more than their trained ear. This is rare. For the vast majority of people the important thing is how successive notes relate to each other. Thus, if an instrument is “in tune” with itself, then it will sound perfectly fine as long as it is not playing at the same time as an instrument that is tuned higher or lower.
It is only in recent history that 440 Hz became “the standard” for tuning. Even today 440 Hz is not always used. For example, in orchestral pieces that include a church organ (the “real” sort, not electronic), then the orchestra will tune to the organ, which for old organs is most probably not tuned to 440 Hz.
Some people believe (and will argue passionately) that one or other particular tuning frequency has “mystical powers”. You can make your own mind up about that.
When the pitch is raised, either with “Change Pitch” or “Change Speed”, all notes are shifted by the same percentage, thus all notes remain “in tune” with all of the other notes.
Whether changing the pitch (only) or changing the speed (pitch and tempo), if the same percentage change is applied, then the pitch change will be the same. That is, a -10.910% change will take notes one (whole) step down whether using Change Pitch or Change Speed.
Changing Pitch or Tempo (one without the other) is difficult for the computer to achieve, so with both of these effects there is likely to be some loss of sound quality. Changing both together (Change Speed) is much easier for the computer to accomplish and there is very little loss of quality (though of course extreme settings will probably sound weird).
Thanks for the great reply, steve!
A few times when toggling song speeds in other programs, I felt like I heard it change into a slightly louder, slightly clearer sound at certain percentages… but I was probably just imagining it.