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 timbre or 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.[a]
In some 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
|Sibelius 5 attacks