Sound Synthesis and Sampling

Martin Russ

• Publisher: Routledge
• Year: 2012
• ISBN:
  9781136122132
• Edition: 3
• Topic: Tecnología e ingeniería
• Subtopic: Ingeniería acústica

Sound Synthesis and Sampling' provides a comprehensive introduction to the underlying principles and practical techniques applied to both commercial and research sound synthesizers. This new edition has been updated throughout to reflect current needs and practices- revised and placed in a modern context, providing a guide to the theory of sound and sampling in the context of software and hardware that enables sound making. For the revised edition emphasis is on expanding explanations of software and computers, new sections include techniques for making sound physically, sections within analog and digital electronics. Martin Russ is well known and the book praised for its highly readable and non-mathematical approach making the subject accessible to readers starting out on computer music courses or those working in a studio.

PART 2
Techniques

Chapter 2

Making Sounds Physically

CONTENTS

Sounds and musical instrument

• 2.1 Sounds and musical instruments
• 2.2 Hit, scrape and twang
• 2.3 Blow into and over

Environment

• 2.4 Sequencing
• 2.5 Recording
• 2.6 Performing
• 2.7 Examples
• 2.8 Questions
• 2.9 Timeline

This chapter deals with sounds that are made by physical methods. This serves two purposes:

• To introduce classification systems for musical instruments and sounds, and thereby, to start the discussion of the analysis and synthesis of sound.
• To introduce the chapter contents with a simple example.

2.1 Sounds and Musical Instruments

There are many ways to classify musical instruments and sounds.

The simplest division uses the performer’s role: using the human vocal tract or interacting with a musical instrument or other objects. This matches the way that music is often described as being vocal, choral, instrumental or orchestral and is supported by descriptions such as ‘full orchestra plus choir’. Unfortunately, human beings are also capable of producing sounds that are outside of the normal description of vocal or choral and can be described as a capella or speech effects: clicks, pops, whistling and noise-based sounds.

Sounds made by interacting with a musical instrument or other objects can be classified using the type of instrument itself or the part that is vibrating.

2.1.1 Instrument

• String instruments
• Wind instruments
• Percussion instruments.

This classification scheme uses the material used to make the instrument as the classifier. It is widely used for orchestral instruments in the West. There are a number of variations and refinements such as brass instruments and keyboard instruments. But it does have limitations, particularly in the context of synthesis, since a synthesizer with a keyboard will be classified as a keyboard, but the same synthesizer controlled by a wind controller will be classified as a wind instrument.

2.1.2 Vibration

This scheme is concerned with what actually makes the sound. There are four basic traditional divisions, with the fifth added more recently.

1. Idiophones, where the sound is produced because the body of the instrument vibrates. Therefore, this group includes percussive instruments such as the marimba, bells and chimes, and wood blocks, as well as less obvious examples such as the triangle and a hand slap on the body of an acoustic guitar.
2. Membranophones, where the sound is produced because a tensioned membrane vibrates. This group includes all the drums with a stretched membrane or skin, plus the kazoo!
3. Chordophones, where the sound is produced because one or more strings vibrate. This group includes the guitar, violin and harp, as well as harpsichords, hammered dulcimers and pianos.
4. Aerophones, where the sound is produced because a column of air vibrates. This group includes the oboe, bagpipes, flutes, horns, trombone and saxophone, as well as the whistle.
5. Electrophones, where the sound is produced because a loudspeaker vibrates. This group includes all electronic instruments, although it generally does not include amplification of another type of instrument, and therefore, the electric guitar is still classified as a chordophone because the vibrating string is the initial source of the vibration.

This classification is easier to understand if you think about genericizing the bit that is vibrating. Aerophones and chordophones both basically vibrate something long and thin in one dimension (1D): a vibrating string or column of air. This produces strong resonances, and therefore, the sounds tend to be pure with a specific pitch. Membranophones are where the membrane can basically vibrate in two dimension (2D), and Idiophones are where the body of the instrument can vibrate in three dimension (3D). As the number of dimensions goes up, the resonances become more complex and weaker, and therefore, the sounds become more complex and with a more diffuse pitch.

This classification scheme is widely used by ethnomusicologists and is known as the Hornbostel–Sachs system. Synthesizers and samplers do not easily fit into this classification scheme, since although easily dismissed as being electrophones, the sound production technique may well be mathematically modeled on any of the other four types, and therefore should be classified appropriately.

In most of the groups mentioned, there are several ways in which the vibration can be caused: hit, scrape, twang and blow. A classification produced by using the vibrating part and the way in which the vibration is caused can also be used.

Classifying sounds rather than musical instruments is required when the sounds are not produced by musical instruments (sirens, wind, gun-shots and explosions are some examples) or are synthetic (bleeps, pips and others) in sound or creation technique. Onomatopoeia (e.g., bang, pop, hiss, …) can be useful for some of the non-instrumental sounds, but pure synthetic sounds can be hard to describe in words ( ‘wee yah oh ooh ’).

In this book, the instrument type, the way of causing the vibration and onomatopoeia will all be used to describe instruments and sounds.

2.2 Hit, Scrape and Twang

Hitting things is probably the first interaction that humans made with potential sound-making objects and is the source of percussion instruments. Whereas hitting a hollow log or stone might be accidental at first, producing a drum with a stretched drum-skin requires design and effort. Hitting the stretched string of a bow is not as immediately satisfying as plucking it, and therefore the piano and the guitar hammer-on are relatively recent inventions. Hitting air is not as hard as it might at first appear: the hand-clap is one example. Sonic booms and whip cracks are somewhere in between hitting air and scraping it (Table 2.2.1).

Scraping pieces of wood, especially hollow ones with textured surfaces, needs some skill and preparation, although door hinges that need oiling can make some very distinctive sounds. Jazz brushes on drum-skins can sound like a sophisticated shaker. Scraping tensioned strings requires a lot of deliberation and knowledge about how to make a resonating body.

Twanging tensioned strings is interesting because it leads to trying to make the sound louder, which leads to resonators, and eventually opens the way for scraping of strings. Twanging membranes is very similar to hitting them, and twanging things sees its modern outlet with the ruler and the African thumb piano.

Table 2.2.1 Types of Sound-Making instrument and examples

	Hit	Scrape	Twang	Blow
Idiophones (3D)	Marimba, wood block	Scraper, waterphone, cuica	Jew's harp, thumb piano	Aeolsklavier
Membranophones (2D)	Drums	Jazz brushes		Kazoo
Chordophones (1D string)	Piano, guitar hammer-on	Violin	Guitar, koto
Aerophones (1D air)				Wind, brass

2.3 Blow Into and Over

Blowing air over the end of a hollow object probably results in experiments with adding extra holes and trying different sizes of tubes. Blowing between two pieces of grass requires more preparation, and combining it with a tube is an intriguing inventive step. Blowing through the lips to produce whistling is just amazing. The whole process of blowing is interesting because of the way in which energy is transferred, often because of turbulence as the air hits a hard edge producing something not unlike scraping!

2.4 Sequencing

Physical instruments can be controlled by a number of sequencer-like mechanisms. One obvious human mechanism is a conductor, whilst a less obvious and more distributed mechanism is bell ringing, which works with patterns of ordering of the playing of the bells. Orchestras, bell-ringers, conductors and other human performers require energy and, usually, a sense of timing or rhythm.

Mechanical playback devices require some source of energy, either a spring, weights or a water wheel (often used in the past for what were called ‘water organs’), a steam engine or other suitable power sources. This powers the musical instrument and the mechanism that converts the stored music from holes into physical controls over the musical instrument through cams and levers. Musical box movements have possibly the simplest arrangement, with pins in a rotating cylinder that twang tuned metal tines, whilst some fairground organs have very complex mechanical linkages to connect to a diverse set of musical instruments ranging from drums to violins. Brass instruments are dif...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• Preface to First Edition
• Preface to Second Edition
• Preface to Third Edition
• Visual Map
• About this Book
• Background
• Techniques
• Applications
• Analysis
• Bibliography
• Jargon
• Index