Sound is created by vibrations that travel as waves through air or another medium. These sound waves can be captured and converted into digital audio files through a process called digitization. The quality of a digital audio file depends on factors like the sampling rate, which is the number of times per second the sound wave is measured, and the sample size or bit depth, which determines how finely variations in the amplitude of the sound wave are recorded. Higher sampling rates and more bits per sample result in better quality recordings but larger file sizes.

2. Introduction
• Sound is one of the most important element of
multimedia.
• It is meaningful “speech” in any language, from a
whisper to a scream.
• It can provide the listening pleasure of music, the
startling accent of special effects or the ambience
of a mood setting background.
• Sound is the terminology used in the analog
form, and the digitized form of sound is called as
audio.

4. Power of Sound
• When something vibrates in the air is moving back and
forth it creates wave of pressure.
• These waves spread like ripples from pebble tossed
into a still pool and when it reaches the eardrums, the
change of pressure or vibration is experienced as
sound.
• Acoustics – the branch of physics studies sound.
• Unit to measure Sound is decibels (db).
• A decibel measurement is actually the ration between a
chosen reference point on a logarithmic scale and level
that is experienced.
• Logarithmic scale is also used to measure earthquakes

5. Power of Sound
• Sound is energy, just like waves breaking on a
sandy beach
• Too much volume can permanently damage the
delicate receiving mechanism behind your
eardrums.
• The perception of loudness is dependent upon
the frequency or pitch of the sound
• At low frequencies, more power is required to deliver
the same perceived loudness as for a sound at the
middle or higher frequency ranges.

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

7. Cello Piano

8. Multimedia Sound Systems
• Macintosh or windows operating system uses
sound to make alert signal.
• System uses beep and warning sounds are
available with the operating system.
• They provide several sounds for the system alert.
• In windows system sound are WAV files and they
are found on windowsMedia subdirectory.
• Windows makes use of WAV files as the default
file format for audio and Macintosh systems use
SND as default file format for audio.

9. Cont…
Macintosh Windows
 Sound Recorders for Windows
 Both Macintosh and Windows PC platform
have the default sound.

10. Sound conversion
Basic Effects

11. Capture & Playback of Digital Audio
Air pressure
variations Digital to
Analogue
Convert Converter
s back
into DAC
Captured via voltage
microphone
Signal is
converted into
binary
Analogue (discrete form)
to Digital ADC 0101001101 Air pressure
Converter 0110101111 variations

12. Recording Audio Files
Recording Audio Files on the pc
Uses either:
ii. Microphone
 connect microphone to the microphone port and record using
sound recorder

13. Recording Audio Files
i. CD-ROM Drive
 Move music files from CD to hard drive or;
 Play the cd and then record using the sound recorder.
ii. Line-in
 pressing play on the audio source, which is connected to the
computer’s audio line-in socket. Record using the sound recorder.
Line in port
on the pc
Audio cable

14. Digital Audio
• Digital audio is created when a sound wave is
converted into numbers – a process referred to as
digitizing.
• It is possible to digitize sound from a microphone, a
synthesizer, existing tape recordings, live radio and
television broadcasts, and popular CDs.
• You can digitize sounds from a natural source or
prerecorded.

15. Cont…

16. Cont…
• Digital audio - data are stored in the form of samples
point.
• Samples represent the amplitude (or loudness) of sound at
a discrete point in time.
• Quality of digital recording depends on the sampling rate,
the number of samples point taken per second (Hz).
High Sampling Rate Samples stored in digital
form
waveform
Low Sampling Rate

17. Digital Sampling
1 second

18. Digital Sampling

19. Digital Audio
• There are three sampling frequencies most often used in multimedia
are 44.1 kHz, 22.05 kHz and 11.025 kHz.
– The higher the sampling rate, the more the measurements are
taken (better quality).
– The lower the sampling rate, the lesser the measurements are
taken (low quality).
• The number of bits used to describe the amplitude of sound wave
when sampled, determines the sample size.

20. Digital Audio
• The value of each sample is rounded off to the nearest integer
(quantization).

21. Digital audio
• If the amplitude is greater than the intervals available, clipping of
the top and bottom of the wave occurs.

22. Cont…
• The quality of your audio is based on the quality of your
recording and not the device on which your end user will
play the audio, so digital audio is device independent.
High Sampling Low Sampling Rate
Rate

23. Cont…
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.
Sampling Rate Sample size

24. Making digital audio files
• Crucial aspects of preparing
digital audio files are:
– Balancing the need for
sound quality against
available RAM and hard
disk resource.
– Setting appropriate
recording levels to get a
high-quality and clean
recording.