01_NF_Ch06 - Addressing the Network – IPv4 Modified from KC Khor, Multimedia Univ. Cyberjaya (KT Lo)
1 CP586 © Peter Lo 2003 Multimedia Communication Introduction to Sound.
-
Upload
shona-tate -
Category
Documents
-
view
215 -
download
0
Transcript of 1 CP586 © Peter Lo 2003 Multimedia Communication Introduction to Sound.
CP586 © Peter Lo 2003 1
Multimedia CommunicationMultimedia Communication
Introduction to Sound
CP586 © Peter Lo 2003 2
Sound and digital audioSound and digital audio Sound is comprise of
Spoken word Voice Music Noise
CP586 © Peter Lo 2003 3
Sound and digital audioSound and digital audio Sound is based on
Energy Transport medium
Transmitter
Energy Pressure
Transport media
CP586 © Peter Lo 2003 4
SoundSound Produced by the vibration of matter. During the vibration, pressure variations are created in the air
surrounding it. The pattern of the oscillation is called a waveform. The waveform repeats the same shape at regular intervals and
each portion is called a period. Sound relies on energy and a transport medium (which is the
air we breathe). Sound is created when changes in air pressure are detected by
the ear drum. Two important characteristics are frequency and amplitude.
CP586 © Peter Lo 2003 5
FrequencyFrequency Rate of sound The reciprocal value of the period. Measured in cycles per second Represents the number of periods in a second and is
measured in hertz (Hz) or cycles per second (cps). A convenient abbreviation, kHz is used to indicate
thousands of oscillations per second. (1 kHz = 1000 Hz) Higher the frequency, clearer and shaper the sound Human hearing capability: 50Hz to 20,000Hz
CP586 © Peter Lo 2003 6
AmplitudeAmplitude The measure of displacement of the air pressure
wave from its mean or quiescent state. The amplitude could also be described as the
height of a given waveform. Power or intensity of the sound Louder the sound, larger in amplitude Stronger in energy
CP586 © Peter Lo 2003 7
Pitch - LoudnessPitch - Loudness Frequency and pitch are related. Pitch is the subjective quality our brains perceive
from frequency. Greater amplitude results when objects are set in
motion with greater force. We derive the relative perception of loudness from
the absolute amplitude of a given sound wave.
CP586 © Peter Lo 2003 8
Computer Representation of SoundComputer Representation of Sound The continuous curve of a sound waveform is not
directly represented in a computer. A computer measures the amplitude of a
waveform at regular time intervals to produce a series of discrete numbers.
Each of these measurements is a sample.
CP586 © Peter Lo 2003 9
Recording SoundRecording Sound To effectively record sound
Twice the frequency that sound can be heard is needed = 40,000Hz
The higher sampling rate, the better quality At lesser rate, subtle change in pitch and tone will
be lost Effective sampling rate
Human voice: 5,000 to 15,000Hz Music: 40,000 Hz
CP586 © Peter Lo 2003 10
Voice and musicVoice and music Consider following three classes of sounds
Voice Talking, not singing
Music Human singing or musical instruments
Sound effect Voice or music More often created by natural events
CP586 © Peter Lo 2003 11
Sample RateSample Rate The rate at which a continuous waveform is
sampled is called the sampling rate. Like frequencies, sampling rates are also
measured in Hz. CD quality : 44,100 Hz Radio quality : 22,050 Hz Telephone quality : 11,025 Hz
CP586 © Peter Lo 2003 12
Audio Production - Audio Production - Conveying RealismConveying Realism Proximity: As you get closer to the source of a
sound the volume should increase. Environment: Sound should be realistic using
ambience and expected acoustics. Enhanced sound effects: Often sound effects are
required to create a realistic feel in a virtual world.
CP586 © Peter Lo 2003 13
Audio Production - Audio Production - Conveying meaningConveying meaning Emotion : dramatic music. Time : Sovereign Hill. Geographic location : didgeridoo, drums. Association : Alarm, Harvey Norman. Signature and continuity : Jaws, 007. Memorability : Star Wars, Dr Who.
CP586 © Peter Lo 2003 14
Editing Digital AudioEditing Digital Audio Trimming : Wave Edit deletes silence. Splicing and Assembly : Cut and paste. Fade In/Out : Volume slowly fades down. Noise Reduction : Dolby Digital Noise Reduction. Signal Processing : Signal processing can allow
you to play sounds backwards and insert sound effects.
CP586 © Peter Lo 2003 15
Real TimeReal Time A real time process is a process which delivers the
results of the process in a given time span. Examples of real time applications may include
missile guidance systems, nuclear reactor protocols and auto pilot technology.
Multimedia often has temporal constraints that require real time scheduling.
CP586 © Peter Lo 2003 16
Real Time Audio (.ram)Real Time Audio (.ram) Using a fast down load process, users with
standard modems can access near CD quality audio and high-quality video normally only available over faster connections.
The buffer decreases sound and image loss on poor Internet connections, improving audio and video quality.
CP586 © Peter Lo 2003 17
Windows WAVWindows WAV Created by Microsoft and IBM. It specifies an arbitrary sampling rate, number of
channels and sample size. It has a plethora of different compression formats. It is a standard used on most Windows machines. Uses application specific blocks.
CP586 © Peter Lo 2003 18
Sound Blaster VOCSound Blaster VOC This is the format used by the Creative Voice
SoundBlaster hardware used in IBM-compatible computers
It specifies sampling rate as a multiple of an internal clock and is not as flexible as the other general formats.
Portions of silence can be added to a sound file.
CP586 © Peter Lo 2003 19
AuAu Sun Audio (.AU) and NeXT. This format became very popular because it is
closely associated with the Unix operating system. Unix is used in most universities as a teaching and
research tool.
CP586 © Peter Lo 2003 20
AIFFAIFF AIFF stands for Audio Interchange File Format
and was developed by Apple for storage of sounds in the data fork.
The Macintosh OS includes support for playing and creating AIFF files.
It allows the specification of sampling rates, sample size, number of channels, and application-specific format chunks.
CP586 © Peter Lo 2003 21
MPEG AudioMPEG Audio MPEG stands for the "Moving Picture Experts
Group”. MPEG compression is a lossy algorithm which
can achieve high rates of compression without noticeable decreases in quality.
Generally considered a Macintosh based sound format.
CP586 © Peter Lo 2003 22
MP3MP3 MP3 is the file extension for MPEG, audio layer 3. Layer 3 uses perceptual audio coding and psycho acoustic
compression to remove all superfluous information. The result in real terms is layer 3 shrinks the original
sound data from a CD by a factor of 12 without sacrificing sound quality.
Because MP3 files are small, they can easily be transferred across the Internet.
CP586 © Peter Lo 2003 23
QuickTimeQuickTime This is the Apple standard for time-based
multimedia files. Versions 1.x support moving pictures, sound and later versions support text.
This standard is often associated with Macintosh computers.
CP586 © Peter Lo 2003 24
MIDIMIDI Musical Instrument Digital Interface is primarily a
standard for communication between musical instruments.
It stores information about which notes were played in a time-line format.
Often used in conjunction with synthesisers to reproduce musical arrangements.
CP586 © Peter Lo 2003 25
AudioAudio
Digitizing sound
CP586 © Peter Lo 2003 26
Digitizing soundDigitizing sound Characteristics for recording sound
Amplitude Sound channels (monaural and stereo) Frequency rate
Standard frequency rates for multimedia computer 11.025 KHz (kilohertz = 11.025 x 103 Hz) 22.5 kHz 44.1 kHz
CP586 © Peter Lo 2003 27
Digitizing soundDigitizing sound Other frequency sampling rates
Especially lower rates 5 KHz and 8 KHz For network applications Sacrifice some quality Significantly reduce amount of data
Amplitude measurement 8 bits (one byte) for 256 levels 16bits for 65,536 levels
CP586 © Peter Lo 2003 28
Digitizing soundDigitizing sound Calculating audio data size
Characteristics Amplitude Sound channels Frequency rates Time
CP586 © Peter Lo 2003 29
Digitizing soundDigitizing sound File size calculation
b = bytes (1 for 8 bits, 2 for 16 bits) Amplitude
c = number of channels (mono – 1 channel, stereo = 2 channels)
Sound channels s = sampling rate in Hertz (cycle per second)
Frequency rates t = time (seconds) File size = b * c * s * t
CP586 © Peter Lo 2003 30
Digitizing soundDigitizing sound Example: file size for 1 minutes, 44.1 KHz, 16 bit,
stereo sound c = 2 (2 channels for stereo) s = 44,100 (frequency) t = 60 (time) b = 2 (2 bytes for 16 bits)
File size = b * c * s * t =2 * 44,100 * 60 * 2 =10,584,000 bytes
CP586 © Peter Lo 2003 31
Digitizing soundDigitizing sound Digital sound characteristics
Frequency Data size Channel Size Comment
44.1 KHz 16 bit Stereo 10.5 MB CD-quality
44.1 KHz 16 bit Mono 5.25 MB Voice or monaural, high quality
44.1 KHz 8 bit Stereo 5.25 MB Best quality for playback on low-end PC
44.1 KHz 8 bit Mono 2.6 MB Good trade-off for voice quality
22.05 KHz 16 bit Stereo 5.25 MB Decent quality
22.05 KHz 16 bit Mono 2.5 MB Good for voice
22.05 KHz 8 bit Stereo 2.6 MB Acceptable for good quality playback
22.05 KHz 8 bit Mono 1.3 MB Thinner sound, TV quality
11 KHz 8 bit Stereo 1.3 MB Lowest quality for music audio
11 KHz 8 bit Mono 1.3 MB Lowest reasonable quality for voice
CP586 © Peter Lo 2003 32
AudioAudio
Digital audio systems
CP586 © Peter Lo 2003 33
Digital audio systemsDigital audio systems The circuitry for digital audio system is
responsible for Convert the audio signal from microphone or other
source into a digital signal Transferring digital data to computer’s storage media Converting digital data from storage into analog
audio signal, if necessary, amplify for playback
CP586 © Peter Lo 2003 34
Digital audio systemsDigital audio systems Digital audio hardware configuration
Audio playeror recorder
Microphone
AudioSpeaker
Digital Audio Circuitry
Data storage
Digital audio file
Analog to digitalconverter
Digital to analogconverter
Amplifier
Line in
Microphone
Line out
Speaker
CP586 © Peter Lo 2003 35
Digital audio systemsDigital audio systems Digital audio software support
Playback Translate the audio into sound
Record Capture audio data from external analog source
Stop Halt playing
CP586 © Peter Lo 2003 36
Digital audio systemsDigital audio systems Fast forward
Move to a later point in the data stream Reverse
Move to a prior point in the data stream Rewind
Move to the beginning of the data stream
Note many of these functions are similar to controls found on standard
commercial audio tape player
CP586 © Peter Lo 2003 37
Digital audio systemsDigital audio systems Sequential access and random access
Sequential access Type must be physically advanced or rewound E.g. tape player
Random access Able to jump to any point in the storage medium and access
data E.g. CD-ROM