Defining the tempo as slow in any piece of music outlines the true intent of the composer. The intent may vary, but it is limited to some select goals. The composer may want the words to have more meaning. She may want to slow down the thoughts of the listener in preparation for an upcoming event in the piece. A slow tempo is often used to create drama in a piece of music. Recently, singer Rihanna sang a hit song called "Umbrella." Several artists covered the song with a much slower tempo to highlight the song's versatility and lyrical significance.
A slow tempo is defined by beats per minute (BPM). It is also defined by measures per minute (MPM). A slow tempo is usually anywhere in the range of 20 to 60 beats per minute. A fast tempo goes up to 200 beats per minute. Italian composers provided descriptors to provide more detail regarding how to play a slow tempo. "Alla Marcia," for example, means to play a specific tempo in a way that resembles a march. Jazz funerals are often compositions that begin with a march tempo that progress into a much faster tempo. The movement of the tempo from slow to fast reflects the initial sadness over the loss of a loved one and the subsequent celebration of life.
There are several terms that define the types of slow tempos. "Lento" is a slow tempo at around 40 to 60 beats per minute. "Grave" is a slow tempo of 20 to 40 beats per minute. "Larghissimo" is a tempo of 20 beats per minute or slower. Funeral marches like "Taps" are often played larghissimo. Some genres, like Gospel music, include compositions with no official tempo, but generally, the slow tempo is the accepted speed at which the song is played. "Amazing Grace," for example, is played with a slow tempo.
The metronome was one of the first tools to define a slow tempo. Technology, however, has given way to software applications that allow composers to manipulate the tempo of music and create slower tempos. Logic Pro, for example, is an application with a feature called VariSpeed. The composer manipulates the speed to test all possible versions of a composition and prevent dissatisfaction with the final composition.