BASICS OF AUDIO AND VIDEO MEDIA 4 th

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BASICS OF AUDIO AND VIDEO MEDIA 4 th semester BCA&B. SC CS by Preetha

BASICS OF AUDIO AND VIDEO MEDIA 4 th semester BCA&B. SC CS by Preetha Rajagopalan. M

MODULE 1

MODULE 1

Characteristics of Sound • Sound is a longitudinal motion consisting of a train of

Characteristics of Sound • Sound is a longitudinal motion consisting of a train of compressions and rarefactions travelling in a medium • Sound waves produce variations of pressure in the medium (represented in micro‐bar). These variations are compressions and rarefactions • When sound waves strike the ear‐drum, these are converted into electrical signals. The auditory nerves carry these signals to the brain which interprets them into sound

 • Amplitude: It is the intensity of compressions and rarefactions produced in the

• Amplitude: It is the intensity of compressions and rarefactions produced in the medium 1 Pa = 10 micro‐bar • Greater the intensity of sound, greater will be the compression and rarefaction • Frequency (f): the number of successive compressions and rarefactions occurring in one second. 16 Hz to 20000 Hz for sound • Time period: Time ( ) T taken to comp g letin one cycle T = 1 / f second • Phase: it indicates the state of motion at a particular instant relative to some reference. It is expressed in terms of angle • Velocity: distance travelled in one second. • Wavelength (λ): the length of space covered in by one cycle of variation • Relationship between frequency, wavelength and velocity v = distance / time = λ / T = fλ

MECHANISM OF HEARING

MECHANISM OF HEARING

STERIOPHONY • Stereos (solid) + phone (sound) = solid sound (3 D sound) •

STERIOPHONY • Stereos (solid) + phone (sound) = solid sound (3 D sound) • When an orchestra is amplified and reproduced, the originality of the sound would be restored. This 3 D reproduction is called stereo • Human system of hearing is stereophonic. If the sounds reaching the two ears differ in time by 10 μs only, the brain will detect the direction correctly

Acoustic Reverberation • Sound suffers reflection, refraction, diffraction and absorption as for any wave

Acoustic Reverberation • Sound suffers reflection, refraction, diffraction and absorption as for any wave motion • The reflected sound will be heard as a distinct echo if time gap between original wave and reflected wave is > 60 ms • The sound persists even after the source has stopped sounding. The gradual fading of the continuing echo is called reverberation. It is different from distinct echo • All natural sound in a hall includes a proportion of continuing echoes. Reverberation is pleasing and should be incorporated in the design of rooms

Growth & Decay of Sound • Growth of sound intensity, I = Im (1

Growth & Decay of Sound • Growth of sound intensity, I = Im (1 – e‐act/4 V Go t o sound test y, m ( e ) where I – intensity at any instant, I m – maximum intensity, a – total absorption, c – velocity of sound, t – time, V – volume of room • Decay of sound, I = I 0 e ‐act/4 V where I 0 ‐ maximum intensity of direct sound Sabine’s equation • Reverberation time, t = 0. 049 V/a (in FPS units) t = 0. 161 V/a (in MKS units)