How do sympathetic strings change the sound of a sitar or sarangi?

In instruments like the sitar and sarangi, sympathetic strings—often made of thin brass or steel—are a fundamental feature that significantly shapes the instrument's timbre.1

These strings are tuned to the notes of the specific raga or mode being performed. When the main melody strings are played, the sympathetic strings vibrate in response to those pitches. This vibration reinforces the upper harmonics, which creates a characteristic bright, silvery sound and adds a unique resonance to the music.1