Multimedia System & Design Ch 4 Audio

Multimedia System and Design
(Audio)
By:
Aized Amin

Audio vs Sound
• Audio is a technical term, referring to sound
coming from a recording, transmission or
electronic device.
• Sound is a generic word and can be caused by
any source.
2Badar Waseer arbabwaseer@gmail.com

What is SOUND?
• Sound comprises the spoken word, voices, music and
even noise.
• It is a complex relationship involving:
– a vibrating object (sound source)
– a transmission medium (usually air)
– a receiver (ear) and;
– a preceptor (brain).

The Power of Sound
• Sound is measured in  dB (decibel)
• Sound waves are known as waveforms.
Something vibrates
in the air
Waves of pressure Ear drums will translate
these changes in wave
Forms as sound

Waveforms
Sound waves are known as waveforms
 A waveform that repeats itself at regular
intervals is called a periodic waveform
 Waveforms that do not exhibit regularity are
called noise

Sound
 A pleasant sound has a regular wave pattern.
The pattern is repeated over and over.
 But the waves of noise are irregular. They do
not have a repeated pattern.

Characteristic of Sound Waves
• Sound is described in terms of two characteristics:
– Frequency (or pitch)
– Amplitude (or loudness)

Frequency
• Frequency is a measure of how many vibrations occur
in one second. This is measured in Hertz (abbreviation
Hz) and directly corresponds to the pitch of a sound.
– The more frequent vibration occurs the higher the pitch of
the sound.
 Optimally, people can hear from 20 Hz to 20,000 Hz (20 kHz)
 Sounds below 20 Hz are infrasonic
 Sounds above 20 kHz are ultrasonic
Low pitch High pitch

Amplitude
• Amplitude is the maximum displacement of a wave from an
equilibrium position.
– The louder a sound, the more energy it has. This means loud sounds have a
large amplitude.
 The amplitude relates to how loud a sound is.
Low amplitude High Amplitude
Quiet Loud

Amplitude
 Sound’s intensity or loudness
 The louder sound, the larger amplitude.

The characteristics of sound
waves
distance
along wave
Cycle
Time for one cycleAmplitude
pitch

Analogue audio
• The name for an electronic signal that carries its
information of sound as continuous fluctuating voltage
value.
• Analog refers to audio recorded using methods that
replicate the original sound waves.
Digitizing
• The process of converting an analog signal to a digital one.
• A sound is recorded by making a measurement of the
amplitude of the sound at regular intervals which are
defined by the "sample rate".
• The act of taking the measurement is often called
"sampling" and each measurement is called a "sample
point".
Analogue to Digital Audio

Capture and playback
of digital audio
Air pressure
variations
Captured via
microphone
Air pressure
variations
ADC
Signal is
converted into
binary
(discrete form)
0101001101
0110101111
Analogue
to Digital
Converter
DAC
Converts
back into
voltage
Digital to
Analogue
Converter

The Power of Sound
• Audio in Macintosh and Windows
– Both Macintosh and Windows PC platform, have
the default system sounds
– MACINTOSH  Chu Toy, Glass, indigo, Laugh,
Simple Beep
– WINDOWS PC  ding.wav, chimes.wav,
logoff.wav, start.wav
• Basic Recording Software
– Both MACINTOSH and WINDOWS have basic recording
software

Digital Audio
• Digital audio data is the representation of sound,
stored in the form of samples point.
• Quality of digital recording depends on the sampling
rate, that is, the number of samples point taken per
second (Hz).
High Sampling Rate
Low Sampling Rate
Samples stored in digital
form
waveform

Digital Audio
• The three sampling frequencies most often used in
multimedia are 44.1 kHz, 22.05 kHz and 11.025 kHz.
– The higher sampling rate, more measurements are taken
better quality.
– The lower sampling rate, lesser the measurements are
taken low quality.
Low Sampling RateHigh Sampling Rate

• 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
 Frequency of sampling
 Measure in Hertz
 The higher sampling rate, higher quality sound but
size of storage is big.
 Standard Sampling rate:
- 44.1 KHz for CD Audio
- 22.05 KHz
- 11.025 KHz for spoken
- 5.1025 KHz for audio effect

 Size Sample
The resolution of a sample is the number of
bits it uses to store a given amplitude value,
e.g.
 8 bits (256 different values)
 16 bits (65536 different values)
 A higher resolution will give higher quality but will
require more memory (or disk storage)

Digital Audio
• Other than that, it also depends on:
– The quality of original audio source.
– The quality of capture device & supporting hardware.
– The characteristics used for capture.
– The capability of the playback environment.

Digital Audio
• More advanced Digital audio editing software:
– One of the most powerful and professional PC-based
packages is a tool called Sound Forge
http://www.sonicfoundry.com/
 Others audio editing software:
 COOL Edit Pro
 Gold Wave
 PROSONIQ SonicWORX
 Samplitude Studio 21Badar Waseer arbabwaseer@gmail.com

Midi Audio
• Musical Instrument Digital Interface
– Before there was a wide use of mp3 and high
bandwidth network, MIDI format audio is popular
when an audio is required to be put on a website.
– Provides a standardized and efficient means of
conveying musical performance information as
electronic data.
– Is a easiest and quickest way to compose our own
score.
• (provided we have knowledge of musical instrument
and composing)
– It is in the form of music score and not samples or
recording.

• MIDI files are very compact and very good for
low-bandwidth delivery.
• Instruments are “piano, drums, bass,
orchestral strings, …”
• It is very attractive for adding MIDI file to your
website with very little download time.

Midi Audio Facts
• Since they are small, MIDI files embedded in web
pages load and play.
• Length of a MIDI file can be changed without
affecting the pitch of the music or degrading audio
quality.
• Working with MIDI requires knowledge of music
theory.

Recording MIDI Files
Recording MIDI Files
• MIDI files can be generated:
– By recording the MIDI data from a MIDI
instrument (electronic keyboard) as it is played.
– By using a MIDI sequencer software application.

Audio File Formats
• MIDI
– *.MID, *.KAR, *.MIDI, *.SMF
• AUDIO DIGITAL
– WINDOWS  *.WAV
– MACINTOSH  *.AIFF
– UNIX  *.AU
– REALAUDIO  *.RA
– MPEG3  *.MP3

MIDI versus Digital Audio
• Advantages of MIDI over digital audio:
– MIDI files smaller that digital audio files.
– Because small file, MIDI files embedded in web
pages load and play more quickly.
– If MIDI sound source are high quality – sound
better.
– Can change the length of MIDI files without
changing the pitch of the music or degrading the
audio quality.

MIDI versus Digital Audio
• Disadvantages of MIDI over digital audio:
– Because MIDI data does not represent the sound
but musical instruments, playback will be accurate
only if the MIDI playback (instrument) is identical
to the device used in the production.
– Higher cost and requires skill to edit.
– Cannot emulate voice, other effects.

Factors considered before adding Sound
to MM Project
1. File formats compatible with multimedia authoring
software being used along with delivery mediums, must
be determined.
2. Sound playback capabilities offered by end user’s system
must be studied.
3. The type of sound, whether background music, special
sound effects, or spoken dialog, must be decided.
4. Digital audio or MIDI data should be selected on the
basis of the location and time of use.

Advantages & Disadvantages of Using
Audio
• Advantages
– Ensure important information is noticed.
– Add interest.
– Can communicate more directly than other media.
– Sound adds life to any multimedia application and
plays important role in effective marketing
presentations.

Advantages & Disadvantages of Using
Audio
• Disadvantages
– Easily overused.
– Requires special equipment for quality production.
– Not as memorable as visual media.

MP3 Format
MP3 is a standard format for music files sent
over the Internet.
MP3s:
– Use one of three MPEG standards for audio
compression
– Can compress an audio file to about one-twelfth
of the space it occupies on a CD with no
significant loss of sound quality

WAV Format
WAV is a standard for sound files on Windows
and Macintosh PCs.
WAVs:
– Do not compress audio as much as MP3s
– Are generally used for sound effects and other
small files

Sound Quality & File Sizes
• Stereophonic (stereo) sound refers to any method of
sound reproduction in which an attempt is made to
create an illusion of directionality and audible
perspective.
– This is usually achieved by using two or more
independent audio channels through a
configuration of two or more loudspeakers in such
a way as to create the impression of sound heard
from various directions, as in natural hearing.
– Thus the term "stereophonic" applies to so-called
"quadraphonic" and "surround-sound" systems as
well as the more common 2-channel, 2-speaker
systems.

Sound Quality & File Sizes
• It is often contrasted with monophonic, or
"mono" sound, where audio is in the form of
one channel
– often centered in the sound field (analogous to a
visual field).
• Stereo sound is now common in
entertainment systems such as broadcast
radio and TV, recorded music and the cinema.

Digital Audio File size
The formulas for determining the size (in bytes) of a
digital recording.
For a monophonic recording:
 sampling rate*duration of recording in seconds*(bit resolution / 8)*1
For a stereo recording:
 sampling rate*duration of recording in seconds*(bit resolution / 8)*2

Digital Audio File size
• Resolution is measured in bits per sample.
Since there are 8 bits in a byte, you have to
divide the bit resolution by 8.)
• Q: What will be file size for a 10-second mono
recording at 22.05 kHz, 8-bit resolution?
22050 * 10 * 8 / 8 * 1
= 220,500 bytes

• What will be file size of 10-second stereo
recording at 44.1 kHz,16-bit resolution ?
44100 * 10 * 16 / 8 * 2
= 1,764,000 bytes.

Compressed File Formats
• There are both compressed and
uncompressed audio file formats
• Compression can be either
– Lossless = The quality of uncompressed audio
equals the quality of original audio file
– Lossy = The quality of uncompressed audio is
lower than the original (e.g. mp3, wma)
• For compression/uncompression matching
algorighm pairs (codecs) are used

Codecs
• A device or program that compresses data to
enable faster transmission and decompresses
received data.
• An audio codec is a device or computer program
capable of coding or decoding a digital data
stream of audio.
• There must be one algorithm for compressing
and one for de-compressing (e.g. before
playback)
• Many codecs have to be installed as plugins for
player/editing applications
• There are many dedicated sites for downloading
codecs

Wave/WAV
• The uncompressed audio format developed by
Microsoft
• Wav files can be either mono or stereo files
and of different sample rates and resolutions
• Many platforms support wav files

UNIX/NeXT audio (.au)
• ”Original” format of networked audio
• Many early versions of browsers and
programming languages (e.g. Java) support
au-files
• Au was originally developed by Sun

AIFF
• Audio Interchange File Format
• Originally the sound format of Amiga & Apple
computers
• AIFF file consists of so-called chunks in which
the qualities of audio + the actual audio data
are stored

MPEG (mp3)
• Nowadays very popular compressed audio
format
• Mp3 is one of the subcategories of MPEG
standard
• Mpeg 1 Layer 3 (mp3) was originally targeted
for transmitting speech over networks
• Several settings can be adjusted when
packaging audio into mp3 format

RealAudio
• .ra/.rm files
• The first audio format to use streaming
technology
• The sound file can be listened while it is been
streamed into the harddrive (The complete
file doesn’t need to be loaded)
• Many internet radio stations use ReadAudio as
the broadcasting format

Other Audio Formats
• Besides the aforementioned there are may
audio formats for different uses:
– WMA
– Ogg
– Monkey’s Audio (.ape)
– FLAC
• In addition the audio editors produce files
which include project information + actual
audio data

Summary
• There are two main types of digital audio
– Sampled audio
• Captured by sampling an analogue waveform at
a set rate
– MIDI data
• Instructions on how to perform some musical
composition
• Sampled audio requires more storage space than
MIDI information

Multimedia System & Design Ch 4 Audio

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Multimedia System & Design Ch 4 Audio