Purpose and interpretation
Dynamics are one of the
expressive elements of music. Used effectively, dynamics help musicians sustain variety and interest in a musical performance, and communicate a particular emotional state or feeling.
Dynamic markings are always relative.
 p never indicates a precise level of
loudness, it merely indicates that music in a passage so marked should be considerably quieter than f. There are many factors affecting the interpretation of a dynamic marking. For instance, the middle of a
musical phrase will normally be played louder than the beginning or ending, to ensure the phrase is properly shaped, even where a passage is marked p throughout. Similarly, in
multi-part music, some
voices will naturally be played louder than others, for instance to emphasis the melody and the bass line, even if a whole passage is marked at one dynamic level. Some instruments are naturally louder than others - for instance, a
tuba playing piano will likely be louder than a
guitar playing fortissimo, while a high-pitched instrument
piccolo playing in its upper register can usually sound loud even where its actual decibel level is lower than that of other instruments.
Further, a dynamic marking does not necessarily only affect loudness of the music. A forte passage is not usually "the same as a piano passage but louder". Rather, a musician will often use a different approach to other aspects of expression like
articulation to further illustrate the differences. Sometimes this might also extend to
tempo. It's important for a performer to be able to control dynamics and tempo independently, and thus novice musicians are often instructed "don't speed up just because it's getting louder!". However, in some circumstances, a dynamic marking might also indicate a change of tempo.
music notation programs, there are default
MIDI key velocity values associated with these indications, but more sophisticated programs allow users to change these as needed. Apple's
Logic Pro 9 (2009-2013) and Avid's
Sibelius 5 (2007-2009) use the following values: Sibelius 5 defines the following values, though these may be adjusted in Sibelius, within the range 0-127:
|Logic Pro 9 dynamics
|Sibelius 5 dynamics