Audio Editing

Audio Editing Developed by Allama Iqbal Open University, Islamabad, Pakistan In association with Commonwealth Educational Media Centre for Asia (CEMCA), New Delhi 2016 These curricula are made available under a Creative Commons Attribution-Share Alike 4.0 License (international): http://creativecommons.org/licenses/bysa/4.0/ Audio Editing Course Code: Not Yet Allocated Units: 1-9 Institute of Educational Technology Allama Iqbal Open University Islamabad Unit one Introduction of Sound and Listening Writer: Muhammad Awais Khan Reviewer: Zahid Majeed Contents Introduction Objectives 1. Basics of sound 2. Waveform characteristics 1. Amplitude 2. Frequency 3. Velocity 4. Wavelength 5. Reflection of sound 6. Diffraction of sound 7. Frequency response 8. Phase 9. Harmonic content 10. Envelope. 3 Sound measurement and its unit 1. Logarithm basics 2. The Decibel 3. Sound pressure level 4. THE EAR 1. Threshold of hearing 2. Threshold of feeling 3. Threshold of pain 4. Taking care of your hearing Self-Assessment Questions References/Suggested Readings INTRODUCTION Dear students to understand the audio recording and its editing first you need to have the basic know how of sound and listening. The following discussion will give you the brief idea about sound and its fundamentals. when we are discussing about the fundamentals we are basically explaining the basic qualities of sounds that how different sounds can be produced and it arrives in to the ears and how the sound waves travel in the form of periodic variations and their depiction in the form of graphical representation. When we make a recording, in effect we’re actually capturing and storing sound into a memory media so that an original event can be re-created at a later date. But to follow this regeneration of event we need to get help from the graphical wave forms and their characteristics will allow you to get help and distinguished between one another. The two basic fundamentals of a graphically presented wave form is its frequency and the amplitude. The content in this unit will explain you the basic range of human hearing in the form of frequency and various range to measure the amplitude of basic wave form cycle and its repetition within the positive and negative amplitudes. This unit will enable you to get a better idea of how the frequency range has a direct relationship over the period of time for determining the difference between low and high frequency ranges. The unit also explains you to get a better idea about the behavior of sound while striking at different surfaces and the relationship of mixing the wave form at different sound angles, the addition of sound at different phases and their results. After having clear background knowledge of a sinusoidal wave form and its characteristics this unit will lead you to more advance level or the actual form of sounds produced by different musical instruments along with their original sound frequencies. In addition to their even and odd multiples called the harmonics which enables you to have a better idea of differentiating between different musical instrumental voicing and the simple and complex waveform mechanism. The unit will also explain the characteristic variation in different musical levels. After having a detailed discussion on sound and its characteristics the chapter will lead you to the next part that is hearing. If we start with the idea that sound is actually a concept that describes the brain’s perception and interpretation of a physical auditory stimulus, the examination of sound can be explained by the characteristics of the ear and how the ear is stimulated by sound. By understanding the physical nature of sound and the basics of how the ears change a physical phenomenon into a sensory one, we can discover how to best convey this science into the subjective art forms of music, sound recording and production. OBJECTIVES: After studying this unit you will be able to: 1. Know about the fundamental of sound 2. Identify the characteristics of a sinusoidal waveform. 3. You can differentiate between a simple and a complex waveform. 4. Know about the musical waveform and its qualities 5. Know about calibration of sound 6. Basics of logarithm. 7. Function of human ear as a transducer 1 THE BASICS OF SOUND Sound is a vibration, or wave, that travels through matter (solid, liquid, or gas) and can be heard. It’s a vibration that propagates as a typically audible mechanical wave of pressure and displacement, through a medium such as air or water. In physiology and psychology, sound is the reception of such waves and their perception by the brain. All sounds are vibrations traveling through the air as sound waves. Sound waves are caused by the vibrations of objects and radiate outward from their source in all directions. A vibrating object compresses the surrounding air molecules (squeezing them closer together) and then rarefies them (pulling them farther apart). Although the fluctuations in air pressure travel outward from the object, the air molecules themselves stay in the same average position. As sound travels, it reflects off objects in its path, creating further disturbances in the surrounding air. When these changes in air pressure vibrate your eardrum, nerve signals are sent to your brain and are interpreted as sound. Sound arrives at the ear in the form of periodic variations in atmospheric pressure called sound- pressure waves. This is the same atmospheric pressure that’s measured by the weather service with a barometer; however, the changes in pressure heard by the ear are too small in magnitude and fluctuate too rapidly to be observed on a barometer. An analogy of how sound waves travel in air can be demonstrated by bursting a balloon in a silent room. Before we stick it with a pin, the molecular motion of the room’s atmosphere is at a normal resting pressure. The pressure inside the balloon is much higher, though, and the molecules are compressed much more tightly together—like people packed into a crowded subway car (Figure 1.1a). When the balloon is popped… “POW!” (Figure 1.1b), the tightly compressed molecules under high pressure begin to exert an outward force on their neighbors in an effort to move toward areas of lower pressure. When the neighboring set of molecules has been com-pressed, they will continue to exert an outward force on the next set of lower-pressured neighbors (Figure 1.1c) in an ongoing outward motion that continues until the molecules have used up their energy in the form of heat. a b c Figure 1.1 Wave movement in air as it moves away from its point of origin. (a) An intact balloon contains pressurized air. (b) When the balloon is popped, the compressed molecules exert a force on outer neighbors in an effort to move to areas of lower pressure. (c) The outer neighbors then exert a force on the next set of molecules in an effort to move to areas of lower pressure … and the process continues. Likewise, as a vibrating mass (such as a guitar string, a person’s vocal chords or a loudspeaker) moves outward from its normal resting state, it squeezes air molecules into a compressed area, away from the sound source. This causes the area being acted on to have a greater than normal atmospheric pressure, a process called compression (Figure 1.2a). As the vibrating mass moves inward from its normal resting state, an area with a lower-than-normal atmospheric pressure will be created, in a process called rarefaction (Figure 1.2b). As the vibrating body cycles through its inward and outward motions, areas of higher and lower compression states are generated. These areas of high pressure will cause the wave to move outward from the sound source in the same way waves moved outward from the burst balloon. It’s interesting (and important) to note that the molecules themselves don’t move through air at the velocity of sound—only the sound wave itself moves through the atmosphere in the form of high-pressure compression waves that continue to push against areas of lower pressure (in an outward direction). This outward pressure motion is known as wave propagation. fig a fig b Figure 1.2: Effects of a vibrating mass on air molecules and their propagation. (a) Compression—air molecules are forced together to form a compression wave (b) Rarefaction—as the vibrating mass moves inward, an area of lower atmospheric pressure is created. 2 WAVEFORM CHARACTERISTICS A waveform is essentially the graphic representation of a sound-pressure level or voltage level as it moves through a medium over time. The simplest kind of sound wave is a sine wave. Pure sine waves rarely exist in the natural world, but they are a useful place to start because all other sounds can be broken down into combinations of sine waves. A sine wave clearly demonstrates the three fundamental characteristics of a sound wave: frequency, amplitude, and phase. In short, a waveform lets us see and explain the actual phenomenon of wave propagation in our physical environment and will generally have the following fundamental characteristics: Amplitude Frequency Velocity Wavelength Phase Harmonic content Envelope. These characteristics allow one waveform to be distinguished from another. The most fundamental of these are amplitude and frequency (Figure 1.3). The following sections describe each of these characteristics. Although several math formulas have been included, it is by no means important that you memorize or worry about them. It’s far more important that you grasp the basic principles of acoustics rather than fret over the underlying math. Figure 1.3: Amplitude and frequency ranges of human hearing.

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