Audio DFT in logarithmical scale24.dec 2010
Sak nebud lenivy a precitaj si anglicky navod. Program pocita a zobrazuje vykonove spektrum zvuku zo zvukovej karty.
This small utility displays power spectrum of audio signal in realtime in logarithmical scale. Takes signal directly from your sound card and calculates discrete fourier transform (DFT) in form of calculation response of FIR filter. It is horribly slow when compared with FFT, but this approach allows the user to design fully customized frequency scale. At first, the program calculates a vector of sines and cosines for every each analysed frequency (vertical bar in window). Then these vectors are multiplied with Hann window function to prevent spectral leakage. A thread takes periodically samples from your sound card and multiplies it with pregenerated sine and cosine table, then it calculates sum of these vectors. Resulting in two real numbers that represent complex number and its absolute value is displayed in application window. All this is done for each displayed frequency. The displayed voltage levels are calibrated with signal generator, probably you will need to correct some coefficients in source code when you want to use this tool as spectrum analyser with voltage indicator. When calculating the spectrum, no overlapping on input signal is applied. So the overlapping factor is 1. Source code is available for download.