by hand or on mounting brackets. Some bands also include electronic instruments such as synthesizers, electric guitars, and bass guitar, along with the requisite amplification. If double-reed or string instruments are used, they are usually placed here, but even this usage is very rare due to their relative fragility. Unusual percussive instruments are sometimes used, including brake drums, empty propane tanks, trashcans, railroad ties, stomping rigs, and other interesting sounds. In modern marching band, there is a use of amplification of the front ensemble to help balance out the wind and drumline sections. The use of synthesizers and electronics in the front ensemble can not only help the front ensemble, or "pit", be heard better by the audience and judges, but it can add soundscapes such as voice-overs to help tell the story of a field show, or to add sound effects (for example, a show about nature could have bird/wind/rain sound samples performed by a front ensemble member playing the synthesizer). A rare inclusion in a marching band that is becoming more popular is the use of electrophones in a marching band. The most common electric instrument seen is a bass guitar, but some schools also use keyboards and lead guitar. To make the electric instruments usable, external power in the stadium is often used, but some groups may use a car-battery mechanism that requires a car battery and a converter to give the instruments and amplifiers remote power. Also, some groups may use a small gasoline-powered generator. Auxiliaries Many bands have auxiliaries that add a visual component to the performance. For ceremonial bands, this could be a traditional color guard or honor guard. For drum & bugle corps and corps-style field bands, this could include dance lines, majorettes, auxiliary units may be collectively referred to as color guard or visual ensemble. Auxiliaries may perform as independent groups. In the early 1970s, color guards began to hold their own competitions in the winter (after the American football season, and before the beginning of the summer drum and bugle corps season). These became known as winter guard. There are also numerous dance competitions in the off-season. The color guard of a marching band or drum and bugle corps may contain sabers, mock rifles, and tall flags. In modern bands, other props are often used: flags of all sizes, horizontal banners, vertical banners, streamers, pom-poms, even tires, balls, and hula hoops