In the omega-wrap machines, the tape is only wrapped around the head for 180 degrees. Two video heads are required, each writing alternate fields. This system has a much smaller signal gap between fields, but the frame-synchronizing pulses are able to be recorded on the tape. Cassette-based systems can only utilize the omega-wrap technique, since it is impractical for an automatic loading system to introduce a loop into the tape. Early omega-wrap systems utilize guard-band recording, but the presence of two heads permits the development of the slant-azimuth technique. Later developments use increasing numbers of heads to record video using smaller drums and for recording HiFi sound as well.