Making Music Expressive with MIDI

What makes a musical performance expressive?

Before I discuss what makes a musical performance expressive, I think the words “expression” and “expressive” need to be clearly defined. “Expression” is the process of representing in a medium, such as words, music, or body language. For example, a facial aspect or vocal intonation indicative of feeling is an expression. To be “expressive” is to effectively convey meaning or feeling.

Although MIDI only allows us to transmit two very specific pieces of information about a note, namely the note number and velocity, some sequenced and live performances using MIDI are more expressive than others. Following are my thoughts on what performers do to make music expressive and how these techniques can be represented in a MIDI sequence.

Are some instruments more expressive than others?

I don’t believe that one instrument is more expressive than another. For instance, one may not think that a bagpipe is a very expressive instrument, but if the emotion I’m trying to convey is a longing for the green fields of Ireland, I’d be hard-pressed to find a more expressive instrument for that purpose.

I do believe, however, that some instruments are able to convey a wider range of emotions. What made the piano, or pianoforte, such a hit when it first arrived on the scene was its ability to be played softly and loudly. Its dynamics gave it a wider range of expression than its predecessor the harpsichord. There is also a broader range of material or literature available for the piano. I’ve heard classical music, jazz, and every style in between played on the piano. Each style conjures up different emotions and imagery. Musical styles have their own languages and rules that give them their musical identities. Each style is a musical expression. What it really comes down to is personal experience. Why? Because a sound has to be associated with a memory to spark an emotive thought in the listener.

What performance characteristics are specific to particular instruments?

This is too broad a topic to cover here, but instruments are generally categorized by their performance characteristics, or family.

• Brass: including trumpets, french horns, trombones, tubas, are usually metal and are played by vibrating one’s lips on a metal mouthpiece. The tones produced can be long or short, depending on the amount of air blown into the instrument, and the tonguing techniques used in performance.

• Woodwind: including flutes, clarinets, oboes, English horns, bassoons, and saxophones, are or were once made of wood, and are played by blowing across a reed, in some cases a double-reed, to produce sound. The exception being the flute, which produces sound by having air blown across an edge.

• Percussion: my principal instrument, can generally be broken down into two categories, non-pitched and pitched.

Non-pitched percussion would include snare drums, bass drums, toms, bongos, congas, timbales, shakers, tambourines, cymbals. Most drums have a membrane stretched over a hollow cylinder, that is struck either with the hand, a stick, or a mallet. Some drums can produce long and short sounds and have wide ranges of expression, like the Brazilian surdo. Cymbals come in many shapes and sizes, and are generally made of a bronze alloy. They can also be very expressive in dynamic range, and in note value.

Pitched percussion would include tubular bells, kalimba, marimbas, crotales, timpani, steel drums, and glockenspiel. These instruments are struck to produce a pitch which can vary in dynamic range and duration as well.

• String: including violins, violas, cellos, double basses, guitars, guqin, dobro, steel guitar, erhu, and oud. These instruments produce sound by being bowed, plucked, or strummed to cause the strings to vibrate. They can produce legato and staccato sound in a wide range of dynamics.

• Keyboard: including harpsichord, piano, and organ, are instruments that are played using a musical keyboard. The harpsichord has strings that are plucked when a key is pressed. It has very limited dynamic range and is most closely associated with the music of the Baroque period. The piano has hammers that strike the strings when a key is pressed. As mentioned above, the piano has a wide dynamic range and the use of pedals further enhances its expressive properties. Organs are keyboards played with the hands or feet to move air through pipes or reeds of various lengths to produce sound. Electric organs generate electrical signals and produce sound through loudspeakers. Organs are diverse and can be used to express a wide range of emotion, from the majesty of high church hymns of old, to the bounce of the jazz organ trios,

• Electronic: include theremins, analog synthesizers, digital synthesizers, electronic drum sets, and virtual instruments, these instruments produced sound by the use of electronics. These instruments are very expressive in that they can be edited to produce an almost infinite variety of sounds.

Are there some parts of an expressive performance that just can’t be represented using MIDI?

There are many parameters that effect how expressive a performance is. Besides the actual characteristics of the sound used (attack, decay, sustain, and release), there are velocity, pitch bends, channel after-touch, and modulations that can add to the effectiveness of a performance.

Quantization and step-editing allow for very precise sequencing of notes. Not quantizing a solo will allow the part to “breathe” and prevent it from sounding too mechanical. Another technique that may be used is the “humanize” function, which takes a quantized performance, and through the use of algorithms, varies the velocities and timing among other parameters to approximate the feeling of a live performance.

Velocity, not to be confused with volume (which is amplitude), is the rate of attack and can alter the sound of a given instrument. For example, I can program a keyboard to produce a bass guitar that sounds plucked when played softly, and “slapped” when played with increased velocity.

Other than the human voice, I think that nearly every part of an expressive performance can be represented using MIDI. We have very powerful tools at our disposal, and we are only limited by our imaginations and ingenuity.

- John Anthony Martinez