Sound Categories

Synthesizers allow you to create virtually any sound you can imagine. Although this may seem like a pretty daunting range of options, musical sounds can be broken down into different categories that help us effectively organize and use them. These categories will also help us create new sounds by giving us some models of how our sounds can be successfully used in a musical arrangement.

Here are three ways that we can organize sound, each helping us think about how to create and use synthesizer sounds:

Musical Function: How a sound is used in a musical arrangement. Melody, bass, accompaniment, textural, and rhythm parts will each play different roles in an arrangement and will have distinctly different characteristics that enable them to work well in those settings. A synthesizer sound that works well for a melody may not be well suited for a bass part.

Instrument Type: The characteristics of a particular group or family of instruments. For the most part, there is a wide variety of instruments that can work for each of the musical functions. We can further classify sounds as belonging to different groups of instruments, such as the traditional string, brass, and woodwind families, or different types of keyboards, guitars, and basses.

Sound Characteristics: The aspects of pitch, timbre, and loudness that define the unique sonic characteristics of each instrument. These are greatly influenced by the physical characteristics of the instrument, as well as the way it produces sound. A basic understanding of these characteristics will go a long way in helping translate what you hear in your imagination to the parameters on a given instrument.

Musical Functions

Although electronic instruments have brought a range of new sounds, for the most part, there is still a core set of musical functions that instruments fulfill in an arrangement. By taking a look at these musical functions and noting their characteristics, we can get some cues on how to design effective musical sounds.

Let's take a look at these common musical functions, and relate their characteristics to some of the synthesis concepts we've been looking at in the last few lessons.

Melody Sounds

The melody is perhaps the most important part of a musical arrangement. It's often the most memorable part of any song or composition. Although the melody itself is the writer’s responsibility, creating a memorable sound is an important part of designing sounds. The type of instrument we'll design and use really depends on the mood of the piece, ranging from mellow, flutelike sounds to aggressive brass sounds. Throughout this range of sounds, we'll generally find two common characteristics. Synthesizer sounds used for melody (1) are generally monophonic, and (2) make use of whatever real-time performance control is available to make them as expressive as possible.

Many acoustic instruments that we consider melody instruments, starting with the human voice, are monophonic. This means that they're only capable of playing one note at a time. Many classic synthesizer sounds are inspired by monophonic instruments and use settings only available in mono mode for legato playing and portamento. Mono mode is also useful when we want to avoid having two notes accidentally sound at the same time; something that would never occur with an acoustic instrument like a flute.

Let’s think about what makes up an expressive melody sound.

The best way to attract a listener’s attention is to change something. Any time we can change any of the elements of sound, pitch, timbre, or loudness while we’re playing a note, we’ll make the sound more interesting and expressive. We can use envelope generators to automatically control changes in timbre and loudness, but these are preprogrammed. For a sound to be truly expressive, it needs to respond in some way to what a performer is doing.

Bass

The bass part in an arrangement fulfills two interconnected roles: (1) it helps define the chord changes, and (2) it works with the drums to define the rhythmic feel. The bass part is usually the lowest sounding note in an arrangement, and needs to be clear and distinct while at the same time filling out the lower range of frequencies. Again, mono mode is useful here. When we play any single line on a keyboard, we often end up accidentally playing two notes at once, which, in the case of a bass sound, makes the part sound muddy.

However, just playing a sound in a low register doesn't make it a good bass sound. To work well rhythmically, a bass sound should have a fast attack that will match that of a drum sound. Once again, the legato functions in a synthesizer's mono mode can help determine how a sound sustains.

Many types of traditional keyboard instruments, such as pianos, organs, and harpsichords, classic electric instruments like a Rhodes or Wurlitzer electric piano or a clavinet, as well as guitars, are commonly used as accompaniment in arrangements. These instruments often work in a rhythm section with the bass, filling out the notes in chord changes, as well as providing a rhythmic feel. As such, they'll need to be polyphonic (able to play more than one note at a time) and will usually have a fast attack time.

Typically, in a fully developed musical arrangement there'll be instrumental parts that provide color by using instruments or voices to play sustained chordal parts. These parts are different from the accompaniment, since they aren't usually used to define the rhythm. In traditional orchestration, groups of instruments called ensembles provide this texture. Ensembles can be made up of similar instruments, as we'd find in a string or brass ensemble, or combinations of instruments from different families, such as woodwinds and strings. In early rock, pop, and r&b arrangements, the organ was the staple textural instrument, with its sustained notes adding color.

Although synthesizers and samplers can emulate the sounds of traditional ensembles, the ensembles we’ve just described can serve as the starting point for another, uniquely electronic type of sound called a pad. Pads are characterized by unnaturally slow attack and release times, and are used to add color to an arrangement. Pads offer you a chance to electronically manipulate sound in interesting ways and should always have at least one or two characteristics that change or evolve while they’re being held. There are a number of good examples of pad sounds for Reason’s Subtractor in the "Pads" folder in the Factory Sound Bank.

Percussion is used to provide the rhythmic feel of a piece. Unlike the other aspects of a musical arrangement, percussion is not tied to any musical scale or key. Although drums are most often used to fill this percussion role, it is possible to use any type of sound that has a quick attack and immediate decay, since percussion sounds are non-pitched. As you can probably imagine, a sampler is a great tool used to produce percussive sounds, allowing us to store libraries of great-sounding drum and percussion sounds from around the world, as well as a wide range of household and industrial sounds, to use in our productions.

Sound Characteristics

As we saw in lesson 1, any sound is made up of three interwoven elements—pitch, timbre, and loudness—the primary colors for anyone making sounds. These elements will ultimately define the characteristics of any sound. In acoustic instruments, they are determined by the physical gestures used to produce sound. Understanding the sound characteristics of different types of instruments, and how they are produced and controlled in the physical world, is the key to realizing them on a synthesizer.

Acoustic and electric instruments all produce sound in response to some physical gesture. An instrument's characteristic sound quality has a tremendous amount to do with the interaction between what an instrument is made of and the physical action that causes it to produce sound.

Some physical gestures we commonly use to produce sounds, as well as instruments we typically associate with them, are listed below.

Gesture	Typical Instruments
Blowing into a tube	brass, reed, woodwinds, flutes
Plucking a string	guitar, bass, strings
Striking a string	piano
Striking a wood or metal bar	marimba, xylophone, pitched percussion in general
Striking a membrane	drums
Bowing a string	violin, viola, cello, string bass

Gestures used to produce sound in some typical instruments.

These performance gestures will have a direct effect on the characteristic sound produced by any instrument. As you may recall, in a subtractive synthesizer, we have distinct modules in the audio signal path that control each element of sound separately. Let's look at some different ways to categorize the elements of sound produced by different instruments.

When we think of the kinds of sounds that we’ll use in building a piece of music, we can separate any sound into two separate categories: pitched and non-pitched musical sounds. Generally speaking we’ll used pitched musical sound for melody and harmony parts, while non-pitched sounds will handle purely rhythmic functions like drums and percussion.

Every sound, whether it’s pitched or non-pitched, has a certain tonal character, a kind of sonic "fingerprint" called timbre. When a sound has a clearly defined tone color, like that of most wind and string instruments, we say it has a harmonic set of partials.

Sounds that are bell-like in nature and would fall into the category of pitched percussion sounds, such as vibraphones and marimbas, have non-harmonic partials. Non-pitched sounds like drums will also have non-harmonic partials.

Some sounds found in nature, like wind or ocean waves, as well as some types of musical sound, like snare drums and the breath sound from a flute, are cases of non-pitched harmonic sound called noise.

The continuously changing shape of a sound’s loudness is its envelope. How a sound is produced will, to a great extent, determine the basic characteristics of its envelope. Sounds that are produced by applying continuous pressure, either from blowing into a tube or bowing a string, offer a great deal of control over how long a note will last. These are sustained sounds, and are characteristic of voice, and of wind and string instruments. Sustained sounds are well suited for playing melodies as well as producing textural sounds.

Sounds produced by plucking a string or striking an object will offer little or no control over how long they'll sustain, and are called decaying sounds. Although percussive sounds like drums and percussion immediately come to mind, a whole range of pitched sounds used for accompaniment, such as guitar and keyboard sounds, are considered decaying sounds.

It’s important to understand that in the world of acoustic instruments, all three of these elements are interrelated, and their behaviors can be characterized by various principles of physics and acoustics. Think of the sound a piano. When we play a note, its sound decays, gradually getting quieter after we’ve struck a note. However, it also changes in timbre, getting duller as it fades away. We can use the very general kinds of observations we’ve just made as starting points in creating a whole range of new musical sounds.