Get position of different frequencies in sound signal Assumed I have a signal where different frequencies appear depending on the time position, i.e. a signal of $440\,\textrm{Hz}$ appears at $t=0$, a signal of $441\,\textrm{Hz}$ appears at $t=1$, a signal of $442\,\textrm{Hz}$ appears at $t=3$. Is it now possible to find out when the different signals appeared, and when they leave again, and relate that to the time position? The normal fft in one dimension just tells me that there are different frequencies, but not which.
My application is, that I have a sound file taken from an interferometer. The sound is generated by the interfering light beams. Different wavelengths generate different interference frequencies, but at different times. Thus I want to get the different frequencies in the resulting signal, and the time when they begin/end. The interference pattern generates a sine wave while interfering.
I don't understand the interferometer setup but have a look at:

Eric Jacobsen &amp; Richard Lyons. DSP Tips &amp; Tricks: The Sliding DFT. IEEE Signal Processing Magazine, March 2003, pp 74–80.

Eric Jacobsen &amp; Richard Lyons. DSP Tips &amp; Tricks: An Update to the Sliding DFT. IEEE Signal Processing Magazine, January 2004, pp 110–111.

You can use the sliding DFT (discrete Fourier transform) to calculate a windowed DFT starting at the time of each sample, not for all frequencies but for just the frequency you are interested about. See the subsections about generalized cosine windows in Wikipedia for the kind of windows that work with sliding DFT. Perhaps you can then use the magnitude and phase information from sliding DFT for your task.