There was made stroboscope from LEDs. LEDs was get from flashlight, The stroboscope drived from soundcard of the computer. There was made simple amplifier with transistors. The program was developed in matlab that can listern microphone and detect frequency of string using fft. Then it generate rectange impulses in sound card with close frequency. output frequency is little different from input frequency to have string slow motion. If the frequencies would be same then string will freeze. There was found that LEDs can generate requered impulses for guitar sound range 80 - 320 Hz with pusle duty 20%. The programm can be used for guitar tuning also. There is a option of fixed output frequency. There is also phase mesurment and stabilization option.