The used modulation is GMSK modulation (Gaussian Minimum Shift Keying). VCOs are used in analog applications such as frequency modulation and frequency-shift keying. Modulation is frequency-shift keying (FSK) with Manchester encoding. This modulation is a kind of continuous-phase frequency shift keying. AFSK differs from regular frequency-shift keying in performing the modulation at baseband frequencies. The bits are encoded using frequency shift keying. This modulation technique is known as frequency-shift keying (FSK). The third type of modulation, frequency shift keying (FSK) was used mainly by radioteletypes. Techniques include Dual Polarization Quadrature Phase Shift Keying (DP-QPSK) and QAM-16. Stacking window managers running on X server required a chroma keying or green screening extension. Before electronic chroma keying, compositing was done on (chemical) film. A small number of beacons transmit Morse code by frequency shift keying (F1A). Routines in the ROM encode and decode data in frequency-shift keying for the cassette. It is sometimes called "staggered quadrature phase-shift keying" ("SQPSK"). Binary phase-shift keying (BPSK) is used by standard GPS and GLONASS signals.