Discrete Fourier Transform of a Two-Tone Signal

sine frequency

f

1

1200

sine amplitude a

0.1

noise amplitude n

0.1

DFT parameters

N

512

1024

4096

window

rect

Hanning

Blackman

scale

dBV

linear

A two-tone signal is the sum of two sine waves plus a noise signal. One sine wave has the frequency 770 Hz and the amplitude 1. The frequency and the amplitude of the second sine wave as well as the noise amplitude are controlled by the sliders.

The signal is sampled at 8 kHz and the discrete Fourier transform (DFT) is calculated. The DFT is scaled such that a sine wave with amplitude 1 results in spectral line of height 1 or 0 dBV. By changing the number of samples,

N

, and by selecting a window function, the frequency resolution and amplitude accuracy of the DFT can be examined.