TFD Scope is a program which realizes observing of audio signals simultaneously in time and frequency domains (TFD). It uses a sound card in your computer. You can see a signal waveform as well its spectrum in real-time. This program can be used for continuous viewing of signals with sound frequencies about from 10 Hz to 20 kHz. For example, connecting microphone to the sound card and running the program you can investigate your own voice peculiarity by observing of waveform and spectrum interrelation. Connecting external signals to Line In socket of TFD Scope can help to estimate parameters of periodic as well as non-stationary signals.