Inverse Fourier Transform Calculator

What this site does. You bring a table of numbers, it gives you numbers back. This page takes a spectrum - a list of frequency bins, each with an amplitude and a phase - and builds the time signal it makes. It runs entirely in your browser — nothing is uploaded, nothing is stored. If you want the reasoning rather than the answer, the inverse Fourier transform article walks through the IDFT, the IFFT and what decides the signal that comes out.

Input is a one-sided spectrum: bins 0 to N/2, with N taken as even (N = 2 × the highest bin). The page mirrors it itself. For an odd N or a full N-bin spectrum, use the advanced calculator.

1. Paste your spectrum into the Input grid — straight from a spreadsheet, or as CSV/TSV text — or import a CSV/TSV file. Three columns: bin k, amplitude, phase in radians. Up to 1,024 bins.
2. A bin you leave out counts as 0, and a blank phase counts as 0. The Fourier transform calculator's output pastes in as amplitudes with phase 0.
3. Press transform. Until then the signal chart stays empty; a paste or an import redraws the spectrum chart at once.
4. Read the result. The Output grid lists sample n and its value, N samples in all. A bin reading A makes a wave of amplitude A. Export saves the Output grid as a CSV/TSV file.

If the spectrum came from a windowed FFT (Hann, say), the signal comes back windowed - tapered towards both ends. An inverse has no window of its own.