When the audio of a piano is sped up, it can create the perception that the piano sounds out of tune. This phenomenon occurs due to a change in the fundamental frequencies of the piano's notes.
A piano's sound is produced by strings that are stretched over a wooden soundboard. When a key is pressed, a hammer strikes the corresponding string, causing it to vibrate and produce sound. The pitch or frequency of the sound is determined by the tension and length of the string.
When the audio is sped up, the playback speed is increased, which in turn increases the perceived frequency of the notes. However, the actual frequencies of the piano strings remain unchanged. As a result, the original harmonics and overtones of the notes no longer align correctly with the increased playback speed.
The perceived "out of tune" sensation arises because our ears are accustomed to hearing certain harmonic relationships in music. When these relationships are disrupted due to the change in playback speed, it can give the impression that the piano is out of tune.
It's important to note that the concept of "tuning" refers to the process of adjusting the tension of the strings to ensure they vibrate at the correct frequencies relative to each other. When a piano is properly tuned, the harmonic relationships between the notes are maintained. However, if a piano is physically out of tune, meaning the strings are not at the correct tensions, speeding up the audio would only exacerbate the problem, making it even more noticeable.