programming with max/msp - Virtual Sound

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Chapter 3T - Noise generators, filters, and subtractive synthesis 3.1 SOUND SOURCES FOR SUBTRACTIVE SYNTHESIS In this chapter we will discuss filters, a fundamental subject in the field of sound design and electronic music, and subtractive synthesis, a widelyused technique that uses filters. A filter is a signal processing device that acts selectively on some of the frequencies contained in a signal, applying attenuation or boost to them. 1 The goal of most digital filters is to alter the spectrum of a sound in some way. Subtractive synthesis was born from the idea that brand-new sounds can be created by modifying, through the use of filters, the amplitude of some of the spectral components of other sounds. Any sound can be filtered, but watch out: you can’t attenuate or boost components that don’t exist in the original sound. For example, it doesn’t make sense to use a filter to boost frequencies around 50 Hz when you are filtering the voice of a soprano, since low frequencies are not present in the original sound. In general, the source sounds used in subtractive synthesis have rich spectra so that there is something to subtract from the sound. We will concentrate on some of these typical source sounds in the first portion of this section, and we will then move on to a discussion of the technical aspects of filters. Filters are used widely in studio work, and with many different types of sound: > Sounds being produced by noise generators, by impulse generators, by oscillator banks, or by other kinds of signal generators or synthesis > Audio files and sampled sounds > Sounds being produced by live sources in real time (the sound of a musician playing an oboe, captured by a microphone, for example) NOISE GENERATORS: WHITE NOISE AND PINK NOISE One of the most commonly used source sounds for subtractive synthesis is white noise, a sound that contains all audible frequencies, whose spectrum is essentially flat (the amplitudes of individual frequencies being randomly distributed). This sound is called white noise in reference to optics, where the color white is a combination of all of the colors of the visible spectrum. White noise makes an excellent source sound because it can be meaningfully filtered by any type of filter at any frequency, since all audible frequencies are present. (A typical white noise spectrum is shown in Figure 3.1.) 1 Besides altering the amplitude of a sound, a filter modifies the relative phases of its components. from “Electronic Music and Sound Design” Vol. 1 by Alessandro Cipriani and Maurizio Giri © ConTempoNet 2010 - All rights reserved 3T 295
3.1 296 Theory dB Fig. 3.1 The spectrum of white noise Paragraph 3.1 - Sound sources for subtractive synthesis Another kind of noise that is used in similar ways for subtractive synthesis is pink noise. This kind of sound, in contrast to white noise, has a spectrum whose energy drops as frequency rises. More precisely, the attenuation in pink noise is 3 dB per octave; 2 it is also called 1/f noise, to indicate that the spectral energy is proportional to the reciprocal of the frequency. (See Figure 3.2.) It is often used, in conjunction with a spectral analyzer, to test the frequency response of a musical venue, in order to correct the response based on some acoustic design. dB � �� Fig. 3.2 The spectrum of pink noise �� frequency � �� frequency 2 Another way to define the difference between white noise and pink noise is this: while the spectrum of white noise has the same energy at all frequencies, the spectrum of pink noise distributes the same energy across every octave. A rising octave, designated anywhere in the spectrum, will occupy a raw frequency band that is twice as wide as its predecessor’s; pink noise distributes equal amounts of energy across both of these frequency bands, resulting in the constant 3 dB attenuation that is its basic property. from “Electronic Music and Sound Design” Vol. 1 by Alessandro Cipriani and Maurizio Giri © ConTempoNet 2010 - All rights reserved
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Alessandro Cipriani • Maurizio Gi
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Alessandro Cipriani • Maurizio Gi
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CONTENTS Foreword by David Zicarell
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Electronic Music and Sound Design -
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LEARNING AGENDA 1T PREREQUISITES FO
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1.1 4 Theory sound or sounds that w
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1.1 6 Theory ��
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1.2 8 Theory Let’s look at a tabl
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1.2 10 Theory time (by measuring th
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1.2 12 Theory By the same reasoning
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1.2 14 Theory If the amplitude of a
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1.2 16 Theory 8 140 the threshold o
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Page 37 and 38: 1.1 52 Practice Paragraph 1.1 - Fir
Page 53 and 54: 1.2 68 Practice Paragraph 1.2 - Fre
Page 55 and 56: Interlude A PROGRAMMING WITH MAX/MS
Page 57 and 58: Interlude A - Programming with Max/
Page 65 and 66: 2T ADDITIVE AND VECTOR SYNTHESIS 2.
Page 67 and 68: Chapter 2T - Additive and vector sy
Page 73 and 74: 2P ADDITIVE AND VECTOR SYNTHESIS 2.
Page 75 and 76: Chapter 2P - Additive and vector sy
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Page 87 and 88: 3.1 298 Theory Paragraph 3.1 - Soun
Page 89 and 90: 3.2 300 Theory Paragraph 3.2 - Lowp
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Page 93 and 94: 3.1 358 Practice Make sure to try s
Page 95 and 96: 3.1 360 Practice Fig. 3.6 The rand~
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Page 101 and 102: IB1 424 Practice defined to be the
Page 103 and 104: IB2 426 Practice From this example,
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Page 107 and 108: 4.2 474 Theory In the example, the
Page 109 and 110: 4P CONTROL SIGNALS 4.1 CONTROL SIGN
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Page 115 and 116: REFERENCES The decision was made to
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programming with max/msp - Virtual Sound

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