The fast fourier transform gives a jumbled order of peak frequency!

I recorded notes from c to d on a musical keyboard and performed fast fourier transform on each of those notes. They had a lot of noise and the notes themselves had a non uniform, non repeating waveform. I logically expected the notes to have a peak frequency in increasing order from c note to b note... but the order that came out was something completely jumbled. What could be the reason for this?

Answer 1

[Walter Roberson]

Notes on keyboards are not pure sine waves. They have attack, sustain, decay, and harmonics. The peak frequency is going to depend on the envelope shape if you are using "peak frequency" to mean "maximum frequency". But perhaps you mean "frequency with the maximum energy" ?

[Samyukta Ramnath]

Peak frequency means frequency with the highest amplitude.