CHAPTER ONE SOUND BASICS. Nitec in Digital Audio & Video Production Institute of Technical Education, College West

Transcription

1 CHAPTER ONE SOUND BASICS Nitec in Digital Audio & Video Production Institute of Technical Education, College West

2 INTRODUCTION

3 LEARNING OBJECTIVES By the end of the lesson, you should be able to: Define the basic properties of sound waves Explain the characteristics of sound transmission into free space Define the inverse square law

4 1.1 WHAT IS A SOUND WAVE? Sound is the result of vibrations of air molecules caused by the motion of an object A sound wave is made when a series of vibrations move through the air (or other medium)

5 Ø Each compression is represented by a peak or crest Ø Each rarefraction is show by the trough Ø The spot where the wave is in neutral position is called zero crossing Ø The overall shape of crest and trough over time is called a waveform

6 1.1WHAT IS A SOUND WAVE Properties of Sound waves: Wavelength Amplitude Frequency Velocity Loudness Envelope Phase Harmonics

7 Funny W.H.A.L.E. Plays Violin ü Frequency ü ü ü ü ü Wavelength Harmonics Amplitude Loudness Envelope ü Phase ü Velocity

8 WAVELENGTH One cycle (or oscillation) is the distance from one peak, of one wave, to the next. Wavelength is the physical distance of a complete cycle Measured in metres Hearing is 20Hz 20kHz 20 Hz cycle = 17 m 20 khz cycle = 2 cm

9 WHAT IS WAVELENGTH? The longer the wavelength, the lower the frequency, thus the lower the perceived sound.

10 AMPLITUDE The difference between the peak pressure and the normal air pressure from one cycle to the next. Technically described as db SPL db = decibel SPL = Sound Pressure Level Increased SPL = Increased volume

11 FREQUENCY Frequency of a wave is the number of times per second that wave cycles occur The closer together the peaks of a wave are, the higher its frequency The frequency of a sound is measured in Hertz (Hz), which means cycles per second Kilohertz (khz) = 1000 cycles per second

12 VELOCITY

13 VELOCITY The velocity of sound describes how much distance a sound wave travels in a given amount of time The speed or velocity of sound in air is approximately 344 meters/ second, 1130 feet/sec. or 770 miles per hour at room temperature of 20 C (70 F) The velocity varies with the temperature of air, such that sound travels slower at higher altitudes or on cold days

14 LOUDNESS Loudness describes the subjective perception of how loud or soft a sound is Amplitude is the measurement of the strength or weakness of air pressure produced by a sound signal The loudness of a sound is not the same as the amplitude of a sound Loudness is the psychological measurement of the magnitude of a sound, which includes everything from its frequency, pressure, harmonics, surface properties within the sound space and duration

15 ENVELOPE The envelope of a sound is the defining characteristic of the shape of a sound All sounds possess a change in amplitude as time increases The features included in an envelope are attack, decay, sustain and release - ADSR

16 PHASE Phase is the time difference between two waveforms in relation to a corresponding point in the wave cycle When a simple waveform moves through one complete cycle, it is said to have traveled through 360 or one complete phase

17 PHASE

18 HARMONICS Harmonics are a series of related frequencies that make up a sound All sounds we hear are a combination of sine waves at different frequencies and amplitudes ü Often called overtones, harmonics are always much quieter than the fundamental ü Combined, they make up about 50% of the sound amplitude

19 WHAT IS A SOUND WAVE SUMMARY What are the 8 basic properties of sound waves? Funny W.H.A.L.E Plays Violin ü Frequency ü Wavelength ü Harmonics ü Amplitude ü Loudness ü Envelope ü Phase ü Velocity

20 WHAT IS A SOUND WAVE SUMMARY What were the 8 properties of sound waves? Wavelength Amplitude Frequency Velocity Loudness Envelope Phase Harmonics

21 1.1 SOUND BASICS RECAP

22 1.1 SOUND BASIC RECAP Physical distance of a complete cycle Distance a sound wave travels in a given time Defining characteristic of the shape of a sound Series of related frequencies that make up a sound Difference between peak pressure and normal atmospheric pressure Number of sound wave cycles per second Subjective perception of sound volume Position of one wave relative to another sound wave ü Frequency ü Wavelength ü Harmonics ü Amplitude ü Loudness ü Envelope ü Phase ü Velocity

23 LEARNING OBJECTIVES By the end of the lesson, you should be able to: Define the basic properties of sound waves Explain the characteristics of sound transmission into free space Define the inverse square law

24 1.2 SOUND TRANSMISSION Types of sound transmission: 1 Isolation 2 Reflection 3 Refraction 4 Diffraction 5 Absorption 6 Interference

25 ISOLATION Isolation is cutting down of sound from leaking into or out of a room. Sound can travel through air or structure. So, an attempt to isolate sound must stop both air-borne and structure-borne sounds. The simplest way to cut down sound is to put a solid wall in its way - the more solid, the better the isolation you'll get.

26 REFLECTION Sound reflections are some of the most recognizable and familiar sonic events. We have all heard reverb in our own bathrooms. Clap your hands and listen to how long it takes for the sound to decay. That is reverb. When a sound wave approaches a flat, hard surface it reflects an identical wave away from the surface at the same incidental angle that it approached it at. This angle is referred to as the angle of incidence.

27 REFRACTION One of the least obvious surface effects is when it refracts when it passes from one medium to another. When a sound signal passes from a thinner medium to a thicker or denser one, it refracts away from the surface of the denser medium.

28 DIFFRACTION Sound can be bended, when an object is greater than the wavelength of an approaching sound wave, the wave will curve around the surface of the object in an attempt to fill in the space behind the obstruction. This creates an acoustic shadow, which results in a severely attenuated sound behind the object.

29 ABSORPTION Sound absorption is extremely important. You have most likely encountered sound absorption if you ever had to fill a room with furniture.

30 HOW SOUND IS TRANSMITTED

31 INTERFERENCE Interference is the addition of two or more waves resulting in a new wave pattern. What actually happens when various sounds combine at a certain place? Your first answer might be that the sound would be louder but in fact sometimes the signal of the sound may be weaker than either of the original sounds. The enhancement or canceling out of the signal is called interference.

32 IN PHASE AND OUT PHASE

33 INVERSE SQUARE LAW Inverse Square Law states that the sound intensity (outward) is inversely proportional to the square of the distance from the point source.

34 1.3 SOUND REPRODUCTION Mono Sound Monaural sound reproduction is single-channel. One microphone, one loudspeaker. From a common signal path Some televisions and radios still work only in mono. The choice to work in mono in this current age is analogous to film makers working in black and white.

35 1.3 SOUND REPRODUCTION Stereo Sound Stereophonic sound is the reproduction of sound using two or more independent audio channels, as in natural hearing. A stereo system has more channels, such as surround 5.1 and 6.1 channel systems. During two-channel stereo recording, two microphones are placed in locations relative to the sound source, with both recording simultaneously. The two recorded channels will be similar, but each will have distinct time-ofarrival and sound-pressure-level information. During playback, the listener s brain uses those subtle differences in timing and sound-level to locate the positions of the objects.

36 REFERENCES sound wave title image sound wave wavelength pic10.png adsr harmonic angle of incidence Room jpg empty room whale joke violin whale