Mariachi songs were longer than the standard three-and-a-half minutes of the then-standard 78 rpm record, forcing the shortening of tunes. Around the same time, the popularity of jazz and Cuban music introduced the trumpet into mariachi, pushing the violins into second place and in some cases, replacing the harp. The most prized of the mariachis remained those from the state of Jalisco, particularly the areas of Cocula and Tecalitlán. They represented Mexico to the people during the Independence Day celebrations in Mexico City in 1933 as well as during Lázaro Cárdenas' election campaign in 1936. The charro tradition was strong in
Mariachi problems recruiting mariachi instructors as many of these do not have required teaching credentials. For this reason, schools often hire trained musicians from outside the mariachi tradition. Many traditional mariachis are concerned that standardization will lead to fossilization and restrict improvisation. Other innovations in the United States have been the incorporation of styles of artists such as Elvis Presley, Freddy Fender and Glenn Miller, as well as the heavy-metal Mariachi band Metalachi. Another is the encouragement of female mariachis including all-female Mariachi groups such as Mariachi Mujer 2000 and Mariachi Divas de Cindy Shea. Mariachi Mujer has performed with Mexican