In digital modulation, an analog carrier signal is modulated by a discrete signal. Rectifiers are also used for detection of amplitude modulated radio signals. Another application of the analytic representation of a signal relates to demodulation of modulated signals. The carrier is modulated by digital signals. Phase provides two pulse waves that can be modulated and distorted. By reducing the duty cycle below 0.5, the output amplitude can be modulated. In addition, continuous waves could be modulated with an audio signal to carry sound. The navigation variable signal is A3 modulated (greyscale). They could also be modulated with an audio signal to carry sound. It also includes technologies such as lasers which transmit data modulated on a light beam. The light forms an electromagnetic carrier wave that is modulated to carry information. All real oscillators have phase modulated noise components. The sounds may further be modulated by membranous coverings and by resonant cavities. Furthermore, semiconductor lasers can be modulated directly at high frequencies because of short recombination time. In addition, transcription factors are often indirectly modulated by drugs through signaling cascades.