My piano is a half step below the standard tuning. I want to listen to and play this song. I calculated that from the 12-range of tones I should slow it down by 1/12 of its frequency but it actually doesn't work in my Audacity. Can you help me, please?
The ratio between the frequencies of successive half-tones in a 12-tone equally tempered scale is 21/12. So to lower the frequencies by a half tone, you need to stretch the file so it is 21/12 ≈ 1.05946309 times as long.
I suggest that you tried to Change Pitch, since this process is available, rather than time-stretch the song. Change Pitch will not change the tempo of the song. If you choose to time-stretch the song, Michael gives you all the information and perfectly answers your question. As far as time-stretching is concerned, depending on the method applied, Audacity will or will not change the pitch. The details evade me as to how it is possible to change the tempo without changing the pitch (or as to how it is possible to change the pitch without changing the tempo). But it is possible. Change Tempo will change the tempo without changing the pitch, while Change Speed will change the speed, affecting tempo and pitch.