THE USE OF DFT WINDOWS IN SIGNAL-TO-NOISE RATIO AND HARMONIC DISTORTION COMPUTATIONS

The discrete Fourier transform (DFT) can be used to compute the signal -to-noise ratio (SNR) and harmonic distortion of a waveform recorder. When the data record contains a non-integer number of cycles of the si ne wave, energy leaks from the sine wave and its harmonics to adjacent frequencies. Reference [1) describes a windowed DFT method for comput ing the RMS value of a sine wave from the magnitude of the main lobe o f its DFT and recommends the use of minimum energy windows. We present criteria for choosing the DFT window. A constraint for the window coe fficients is derived to insure that quantization error does not influe nce the estimate of the amplitude of a sine wave from the main lobe of its DFT.