Negative frequency
![A negative frequency causes the sin function (violet) to lead the cos (red) by 1/4 cycle.](/Images/godic/202501/29/Negative_frequency.svg3612.png")
![The vector (cos t, sin t) rotates counter-clockwise at 1 radian/second, and completes a circle every 2π seconds. The vector (cos −t, sin −t) rotates in the other direction (not shown).](/Images/godic/202501/29/Unit_circle.svg3612.png")
![](/Images/godic/202501/29/Aliasing_between_a_positive_and_a_negative_frequency3613.png")
The concept of negative and positive frequency can be as simple as a wheel rotating one way or the other way: a signed value of frequency can indicate both the rate and direction of rotation. The rate is expressed in units such as revolutions (aka cycles) per second (hertz) or radian/second (where 1 cycle corresponds to 2π radians).