Although some high-definition broadcast systems may use a standard-definition reference signal as a generator-locking reference signal, the use of tri-level synchronising pulses directly related to the frame and line rate is increasing within HD systems. A tri-level sync pulse is a signal that initially goes from 0 volts DC to a negative voltage, then a positive voltage, before returning to zero volts DC again. The voltage excursions are typically 300 mV either side of zero volts, and the duration each of the two excursions is the same as a particular number of digital picture samples.
although some high-definition broadcast systems may use a standard-definition reference signal as a generator-locking reference signal the use of tri-level synchronising pulses directly related to the frame and line rate is increasing within hd systems a tri-level sync pulse is a signal that initially goes from 0 volts dc to a negative voltage then a positive voltage before returning to zero volts dc again the voltage excursions are typically 300 mv either side of zero volts and the duration each of the two excursions is the same as a particular number of digital picture samples