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Time: 20 hours
Level: Introductory
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 Introduction Resource- This unit contains material that is essential to learning about music technology. Here you will explore the concept of sound and be introduced to the physics behind travelling pressure waves as the physical...
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- 1.1 Music and technology Resource
- Music technology in one guise or another is part of everybody's life, because music is a part of almost everybody's life. For instance, if you are an instrumental performer of music, professional or not,...
- 1.2 What is sound? Resource
- In the previous section I posed a question: what is sound? Take a few minutes to think about this. This may seem a straightforward question, but in fact sound is a rather more complicated thing to pin...
- 1.3 Describing sound Resource
- Let's now take a closer look at my list of categories from Activity 3, starting with item (a). In each of my descriptions of this sort, I referred to the source–cause of the sound: that is, an object or...
- 1.4 Summary Resource
- The close relationship between music and technology is not new, and is not confined to electronically generated or computer-generated music. Historically there is a long association between music and technology,...
| | | | | 2 Sinusoidol pressure waves
- 2.1 The importance of sine waves Resource
- For much of the rest of this unit we shall be concerned with the properties of a type of sound wave that when represented as a graph has a characteristic shape known as a sine wave. Figure 1 shows you...
- 2.2 Pressure in the atmosphere Resource
- The sounds we hear generally consist of rapid fluctuations of air pressure in the atmosphere that surrounds us. Sound can also be transmitted through other media, for instance water, so not all sound consists...
- 2.3 Pressure waves and cycles Resource
- In this section we shall be looking at the behaviour and properties of pressure waves in the atmosphere.
- 2.4 Period Resource
- You saw in Section 2.3 that the prongs of the tuning fork vibrate cyclically. You also learned that a cycle of the prongs' vibration is a complete sequence of motion up to the point at which the motion...
- 2.5 Wavelength Resource
- So far we have seen that sound is a pressure wave, and that the spacing of the pressure variations is related to the period of vibration of the source.
- 2.6 Pressure variations in one place Resource
- So far, when we have been thinking about pressure waves we have visualised a pattern of pressure variations extending through space, and travelling away from the source of the vibration.
- 2.7 Summary Resource
- Pressure in the air is related to how closely packed the molecules are. Other things being equal, more closely packed molecules are at a higher pressure than more dispersed molecules. Sound is associated...
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- 3.1 Frequency and period Resource
- In Figure 11 you saw that waveform (b) had a much shorter period than waveform (a). Hence waveform (b) completes more cycles of oscillation in a second than does waveform (a). Waveform (b) is said to have...
- 3.2 Summary Resource
- The number of cycles of oscillation per second, both for a vibrating source and a pressure wave, is known as the frequency, symbol f Frequency is specified in hertz (Hz) or kilohertz (kHz). One hertz is...
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- 4.1 The experimental result Resource
- One way to establish the speed of sound is to measure it experimentally. That is, one measures how long the sound takes to travel a known distance, and from this works out the speed. The answer turns out...
- 4.2 Frequency, wavelength and the speed of sound Resource
- The speed of sound has a joint relationship with both the wavelength and the frequency of the sound. To see why, recall that at the end of Section 2.5, in connection with the wave produced by a tuning...
- 4.3 Summary Resource
- The speed of sound in air, symbol v, is approximately constant at 340 metres per second. (You do not need to memorise this value.) As temperature increases, the speed increases slightly.
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- 5.1 Phase and phase difference Resource
- In this section I am considering sine waves that have the same frequency, but are out of step with each other.
- 5.2 Cancellation and reinforcement Resource
- I have shown that a phase difference between two points in space arises as a natural consequence of the finite time it takes a pressure wave to travel between two points in space. This is not the only...
- 5.3 Summary Resource
- The term phase is used to refer to the part of a cycle that an oscillating system is in at a particular moment. For two sine waves of the same frequency that are not in step, one wave lags or leads the...
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- 6.1 Defining amplitude Resource
- Another important property of a sine wave we need to be able to specify is its amplitude. In essence, the amplitude of a sine wave is its size. Unfortunately there are various ways of defining what is...
- 6.2 Practical units of amplitude Resource
- The amplitude of a sine wave is measured in whatever units are used to calibrate the vertical axis, as you saw in connection with Figures 18 and 19. Nearly all the graphs you have seen so far in this unit...
- 6.3 Root-mean-square amplitude Resource
- One drawback of the amplitude as I have defined it is that although it allows the relative sizes of sine waves to be compared, it does not give a good idea of what a sine wave can deliver in absolute terms....
- 6.4 Summary Resource
- Amplitude refers to the size of a sine wave. It can be defined in various ways, but a standard definition is that it is the maximum value of a wave's departure from its average value. (The average value...
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- 7.1 The subjective experience Resource
- Two of the properties of sound that we have examined from an objective stance, frequency and amplitude, have a fundamental importance to our appreciation of sound and music. In this section I want to look...
- 7.2 Summary Resource
- Pitch and loudness are subjective properties of sound. Pitch is closely correlated with frequency, and loudness is closely correlated with amplitude. However, under certain circumstances, slight changes...
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- 8.1 The octave sound Resource
- One feature of pitch that seems to be universal to all cultures is that for musical purposes the pitch range is divided into discrete steps: for instance, the notes of a scale. This is not to say that...
- 8.2 Octave pitch and frequency increments Resource
- Because a doubling of frequency corresponds to an octave increase of pitch, it follows that there is no constant increment of frequency that always corresponds to a one-octave increment of pitch. That...
- 8.3 Summary Resource
- A fundamental musical and acoustical relationship is the octave. Pitches that are one or more octaves apart are heard musically as different instances of the same sound. A one-octave increase in pitch...
| | | | | 9 The ranges of human hearing
- 9.1 Frequency range Resource
- The lowest frequency humans can hear is approximately 20 Hz. The upper limit for humans is nominally 20 000 Hz (20 kHz), but this limit tends to decline with age, and for most of us it is well below this...
- 9.2 Dynamic range Resource
- The quietest sound we can hear corresponds to a pressure wave with an amplitude of about 10 μPa, which is a very small pressure amplitude indeed. It is about 0.000 000 01 per cent of nominal atmospheric...
- 9.3 Summary Resource
- The nominal frequency range of human hearing is 20 Hz to 20 kHz, though most people cannot hear to 20 kHz. However, the pitches used in music correspond roughly to frequencies in the range from 20 Hz to...
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- 10.1 Introduction Resource
- For a variety of reasons, not least the very wide dynamic range of human hearing, the decibel (symbol dB) is often used as a unit for the amplitude of sound waves. The decibel is also used in other contexts,...
- 10.2 Adding decibels Resource
- A feature of decibels is that adding two decibel values is equivalent to multiplying the ratios they represent. To see how this comes about, consider another context in which a decibel measurement is often...
- 10.3 The decibel as a measure of sound amplitude Resource
- As I mentioned earlier, because a decibel is a way of expressing a ratio, it cannot by itself express the absolute size of anything. To express absolute values it must be referred to a fixed reference...
- 10.4 Summary Resource
- The decibel (symbol dB) is a way of expressing a ratio. It is based on logarithms, and so adding decibels is equivalent to multiplying their corresponding ratios. Decibels can be used to express absolute...
| | | | | References and Acknowledgements | | |
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