I am a little familiar with Fourier Analysis, but I don't know where to get tools to get the answer to this question: Consider a discrete signal A[0..N-1], consisting of N samples. Suppose we Fourier transform it and get a series of harmonics. Now, consider the discrete signal A[1..N], that is equal to signal A[0..N-1] on the corresponding indices [1..N-1], and has the next sample AN added to it, to obtain N indices. We subject the second signal to Fourier transform too. Will the set of harmonics of the first signal and the set of harmonics of the second be quite similar (having similar amplitudes), or could they differ considerably? I relate this to a spectral analyser display of audio signals. If the Fourier transform is done on a fixed interval, each next transform done from one sample further on, the (virtual) frequencies in the audio signal shouldn't jump around too much on that instance, should they? I am not sure about white noise though. I hope the question is clear. Answers are very welcome!