Sound

IntroductionIntroduction

• Sound is one of the most important element of Sound is one of the most important element of multimedia. multimedia.

• It is meaningful “speech” in any language, from a It is meaningful “speech” in any language, from a whisper to a scream.whisper to a scream.

• It can provide the listening pleasure of music, the It can provide the listening pleasure of music, the startling accent of special effects or the ambience startling accent of special effects or the ambience of a mood setting background.of a mood setting background.

• Sound is the terminology used in the analog Sound is the terminology used in the analog form, and the digitized form of sound is called as form, and the digitized form of sound is called as audio.audio.

Power of SoundPower of Sound• When something vibrates in the air is moving back and When something vibrates in the air is moving back and

forth it creates wave of pressure. forth it creates wave of pressure. • These waves spread like ripples from pebble tossed These waves spread like ripples from pebble tossed

into a still pool and when it reaches the eardrums, the into a still pool and when it reaches the eardrums, the change of pressure or vibration is experienced as change of pressure or vibration is experienced as sound.sound.

• Acoustics – the branch of physics studies sound.Acoustics – the branch of physics studies sound.• Unit to measure Sound is decibels (db).Unit to measure Sound is decibels (db).

• A decibel measurement is actually the ration between a A decibel measurement is actually the ration between a chosen reference point on a logarithmic scale and level chosen reference point on a logarithmic scale and level that is experienced. that is experienced.

• Logarithmic scale is also used to measure earthquakesLogarithmic scale is also used to measure earthquakes

Power of SoundPower of Sound

• Sound is energy, just like waves breaking on a Sound is energy, just like waves breaking on a sandy beachsandy beach

• Too much volume can permanently damage the Too much volume can permanently damage the delicate receiving mechanism behind your delicate receiving mechanism behind your eardrums.eardrums.

• The perception of loudness is dependent upon The perception of loudness is dependent upon the frequency or pitch of the soundthe frequency or pitch of the sound• At low frequencies, more power is required to deliver At low frequencies, more power is required to deliver

the same perceived loudness as for a sound at the the same perceived loudness as for a sound at the middle or higher frequency ranges.middle or higher frequency ranges.

SoundSound

• Sound is energy, caused by molecules Sound is energy, caused by molecules vibrating vibrating

Cello Piano

Multimedia Sound SystemsMultimedia Sound Systems• Macintosh or windows operating system uses Macintosh or windows operating system uses

sound to make alert signal.sound to make alert signal.• System uses beep and warning sounds are System uses beep and warning sounds are

available with the operating system.available with the operating system.• They provide several sounds for the system alert.They provide several sounds for the system alert.• In windows system sound are WAV files and they In windows system sound are WAV files and they

are found on windows\Media subdirectory.are found on windows\Media subdirectory.• Windows makes use of WAV files as the default Windows makes use of WAV files as the default

file format for audio and Macintosh systems use file format for audio and Macintosh systems use SND as SND as default file format for audio.default file format for audio.

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Sound Recorders for Windows Both Macintosh and Windows PC platform

have the default sound.

Macintosh Windows

Sound conversion

Basic Effects

Capture & Playback of Digital AudioCapture & Playback of Digital Audio

Air pressurevariations

Captured viamicrophone

Air pressurevariations

ADC

Signal isconverted into

binary(discrete form)01010011010110101111

Analogueto DigitalConverter

DAC

Converts back

into voltage

Digital toAnalogueConverter

Recording Audio FilesRecording Audio Files Recording Audio Files on the pc

Uses either:

i. Microphone

connect microphone to the microphone port and record using

sound recorder

Recording Audio FilesRecording Audio Filesii. CD-ROM Drive

Move music files from CD to hard drive or;

Play the cd and then record using the sound recorder.

iii. Line-in

pressing play on the audio source, which is connected to the computer’s audio line-in socket. Record using the sound recorder.

Audio cable

Line in port on the pc

Digital AudioDigital Audio

• Digital audio is created when a sound wave is Digital audio is created when a sound wave is converted into numbers – a process referred to as converted into numbers – a process referred to as digitizing. digitizing.

• It is possible to digitize sound from a microphone, a It is possible to digitize sound from a microphone, a synthesizer, existing tape recordings, live radio and synthesizer, existing tape recordings, live radio and television broadcasts, and popular CDs. television broadcasts, and popular CDs.

• You can digitize sounds from a natural source or You can digitize sounds from a natural source or prerecorded.prerecorded.

Cont…Cont…

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• Digital audio - data are stored in the Digital audio - data are stored in the form of samples form of samples

pointpoint..

• Samples represent the Samples represent the amplitudeamplitude (or loudness) of sound at (or loudness) of sound at

a discrete point in time.a discrete point in time.

• Quality of digital recording depends on the Quality of digital recording depends on the sampling ratesampling rate, ,

the number of samples point taken per second (Hz).the number of samples point taken per second (Hz).

High Sampling Rate

Low Sampling Rate

Samples stored in digital form

waveform

Digital SamplingDigital Sampling

1 second

Digital SamplingDigital Sampling

Digital AudioDigital Audio

• There are three sampling frequencies most often used in multimedia There are three sampling frequencies most often used in multimedia

are 44.1 kHz, 22.05 kHz and 11.025 kHz.are 44.1 kHz, 22.05 kHz and 11.025 kHz.

– The The higher the sampling ratehigher the sampling rate, the , the more the measurementsmore the measurements are are

taken (better quality).taken (better quality).

– The The lower the sampling ratelower the sampling rate, the , the lesser the measurementslesser the measurements are are

taken (low quality).taken (low quality).

• The number of bits used to describe the amplitude of sound wave The number of bits used to describe the amplitude of sound wave

when sampled, determines the sample size. when sampled, determines the sample size.

Digital AudioDigital Audio• The value of each sample is rounded off to the nearest integer The value of each sample is rounded off to the nearest integer

(quantization).(quantization).

Digital audioDigital audio

• If the amplitude is greater than the intervals available, If the amplitude is greater than the intervals available, clippingclipping of of the top and bottom of the wave occurs.the top and bottom of the wave occurs.

Low Sampling RateHigh Sampling Rate

Cont…Cont…• The quality of your audio is based on the quality of your The quality of your audio is based on the quality of your

recording and not the device on which your end user will recording and not the device on which your end user will play the audio, so digital audio is play the audio, so digital audio is device independentdevice independent..

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Sampling Rate Sample size

o Quality factors for digital audio file :

1. Sampling Rate

2. Sample Size (resolution)

the number of bits used to record the value of a sample in

a digitized signal.

Making digital audio filesMaking digital audio files

• Crucial aspects of preparing Crucial aspects of preparing digital audio files are:digital audio files are:

– Balancing the need for Balancing the need for sound quality against sound quality against available RAM and hard available RAM and hard disk resource.disk resource.

– Setting appropriate Setting appropriate recording levels to get a recording levels to get a high-quality and clean high-quality and clean recording.recording.