UNIT – II INTRODUCTION TO DIGITAL MEDIUM
Analog Signal: Continuously varying signal, used to record some media signal. Digital Signal: Signals constructed solely using zeros and ones, which the computers can understand and handle. Digitizing: The process of converting analog signals to digital signals by way of taking discrete samples. Sampling rate: The time interval taken between two samples of the original analog data, during digitizing. The sampling rate is mearsured in terms Hertz (Hz),whitch is the term for c ycles per second. Sampling Size: The number of Computer bits (Zeros and Ones) required to represent a given signal in digital form. DIGITAL AUDIO TECHNOLOGY Computers and Sounds Computers were making sounds even before the advent of multimedia and digital • audio technology. technology. Small beep sounds meant that the user was trying in vain , to accomplish a task that the • computer has fails to recognize The computer beep was actual a warning to notify that the user. • Sound louder than a polite beep meant something much worse – may be the paper deck • had slipped in the printer carriage again.
Definition: Digital audio is the technology, by which sound signals are represented as a series of binary digital data i.e., zero and ones which the computers understand and comprehend.
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Once digitalized sound can be processed like any other binary files , using the relevant editing and play back software.
WHY GOING DIGITAL?
The primary purpose of digitizing the sounds is to make the multimedia computer understand and comprehend with the audio signals, digital audio has its own advantage over its predecessor, analog audio. 1.
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Digital audio is less susceptible to degradation or distortion, because the entire transmission and all other other transaction process takes place as electronic electronic signals, avoiding the intervention of air or any other mediums. Thus the quality of the parent signal is maintained. Editing audio with computers computers makes makes cutting, pasting and manipulating of the the parent signals, very easy. Also, a lot of special effects like the echo can be artificially added, without the need of any other hardware. Digital audio is of superior quality during reproductions, because of non intervention of air and other loss incurring mediums. Digital audio can be stored as digital data, in reliable mediums like like the CD-ROM-thus extending their shelf life to more than fifty years on an average without losses. •
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Digital audio files are constructed by receiving analog signals, taking out samples of the same at certain intervals and reconstructing the pattern using zero and ones. Special processing chips and electronic circuits, technically called an alog to digital convertor are used to accomplish this.
AUDIO RECORDING & AUDIO PLAYBACK
ANALOG TO DIGITAL AUDIO (ADC PROCESS)
DIGITAL TO ANALOG AUDIO (ADC PROCESS)
DIGITAL AUDIO PARAMETERS
Digital audio samples characteristics are controlled by two main attributes of the process 1. Audi Audio o samp sampli ling ng rat ratee 2. Audi Audio o samp sampli ling ng siz sizee Audio sampling rate: The rate at which sound samples are recorded from the incoming analog audio source • and is record in X-Axis It is measured in of Hertz. • The higher the frequency , the better is the recorded signals , if more number of • samples are taken during a given time of interval. The wave reconstruction is relatively smooth and resembles the original signal to a better d egree. The three sampling rates or sampling frequencies that are often used in multimedia • audio arena and are meant meant for CD quality Audio. Audio sampling size Audio sampling size refers to the number of z eros and ones used to record reco rd the • incoming signals and is recorded along a long the Y-Axis. Y-Axis. This size depends upon the bits of data your digital sound systems can handle. • An 8 bit sound system can record signals at around 256 quantum steps. • Larger audio samplings size can produce better q uality sounds. • A 16 bit sound system will perform modestly well on all normal usages, though • professional recording demands 32 bits or more. MONO AND STEREO AUDIO CHANNELSING •
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In Mono audio recording / playback , same sound signals are sent to both Left and Right channels of the recorders/speakers; But in stereo, they are different. Digital Audio files also handle stereo sounds, by incorporating necessary details in their header section. If the recording is specified as stereo, then, during playback, alternating byte samples are sent to two speakers after conversion. conve rsion. Sampling size reduces as the number of o f bits that have shared by two incoming signals instead of one. Stereo is advisable only if you need high quality music.
DIGITAL RECORDING PITFALLS
Two types of problems can be anticipate in digital recording process
1. Quantization: The value of each sound sample, during A D C process, is rounded off to the nearest integer value. This is called quantization and it sometimes sometimes produces an unwanted background noise 2. Clipping: During A D C, if the amplitude of the samples are greater than the intervals available, the wave is clipped in the top and the bottom. This is called clipping and it sometimes results in severe distortions of fine music.
The process parameter should be carefully assigned. So as to avoid kinds of pitfalls DIGITAL AUDIO FILE SIZES An approximate idea of the disk space requirements for a specific digital audio recording, c an be calculated using the following formula:
Disk space required per second of recording (in Bits) = Sampling Size (in Hz)*Sampling rate(in Bits)*Channel Multiplication Factor Where Channel Multiplication factor=1 for Mon recording and 2 for Stereo DIGITAL AUDIO PLAY BACK •
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The digital files are converted back to their parents p arents form viz analog signals and are fed into the speakers. The process is necessarily a reversal of ADC i.e. digital to analog conversion (DAC). The digital data that’s converted back, the result are generally rich. The basic digital sound manipulation systems in almost the entire current multimedia computer are usually built up with their own a mplifiers circuits and can handle around 4 watts at 4 ohms on each channels. ANALOG TO DIGITAL CONVERTION
COMPUTER
D R I V E R
Microphone
I N T E R F A C E DIGITAL TO ANALOG CONVERTION
Speakers
2.1 THE SOUND CARD FUNDAMENTALS THE AUDIO CARDS FAMILY INTRODUCING THE FAMILY •
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The digital recording of the analog source signals is achieved by means of electronic circuits called the analog to digital converters(ADC) converters(ADC) and that during playback The digital signals are converted back to their parental form by means of the digital to analog converter (DAC) before fed into the speakers. All these conversion circuits and a host ho st of other electronic circuits that performs various other audio manipulation functions, are bundled into the multimedia computer , in the form of electronic printed circuit boards these PCBs are usually called as the Audio Cards
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Digital file formats have evolved for multimedia audio. Wave file format Wav For windows or the audio interface file format (files with .AIF extension for the use of Apple Macs. And playing back and reading such multimedia audio files. Audio cards should also be stressed that audio cards functionalities extend much beyond mere audio recording and digital playback
THE THREE MUSKETEERS: Three main types of audio cards are mainly used in the multimedia application.
SOUND CARD
COMPUTE R
MIDI INTERFACE CARD
WAVE SYNTHESIS CARD
Music, speech, etc.
Electronics instruments ( keyboard )
Music, (special effects )
SOUND CARDS: •
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Sound Cards are basically meant for Digital audio recording/Amplification/playback and a number of other fundamental audio functions. The other two type of cards are dependent on the sound cards and cannot function without them. The most famous among the bunch of sound cards currently available in the market, i8s creative sound blaster blaster series is cards.
THE MIDI INTERFACE INTERFACE CARDS: MIDI cards are special purpose audio cards exclusively meant for recording music • directly from electronic instruments mostly the electronic keyboards. The keyboard must be compatible with MIDI • In general, only the higher end keyboards supports MIDI and or not others. • MIDI cards record music in a very special format that’s that’s exclusively meant for • electronic synthesized music. The greatest attraction being their smallest dial size as compared to their sound card • counterparts-which make them ideal for storing music data that a re comparatively very long and broadcast like internet Disadv :- MIDI is that they cannot record audio other than electronic music, like • speeches or wind instruments. THE WAVE SYNTHESIS CARDS: The wave synthesis cards are also special purpose Audio cards-They are exclusively • meant for professional musicians and not for the average multimedia users. The Wave Wave Synthesis cards, in a way, way, go much beyond mere digital recording in that • they can create professional music on their own, withou t the aid of any music instruments. The music created is much superior quality, since the music is created just by adding • and deleting Notes. THE SOUND CARD FUNDAMENTALS FUNDAMENTALS Sound card are a re basically meant for digital Audio Recording, Amplification and playback. AUDIO SYNTHESIS TECHNOLOGY The process by which a sound card creates music is called the sound synthesis or the • audio synthesis. There are two fundamental types of sound synthesis technology • FM synthesis and the wave table synthesis. FM Synthesis: The technique of blending around with a range of frequency modulations to produce • audio that resembles the original analog sound data.
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The finial outputs sounded much like ‘electronic generated’ audio pluses.
WAVE TABLE SYNTHESIS: •
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The technique of building a wide variety of built in sound samples (actual recording) of various music instruments and reconstructing the sounds by looking up for samples. When a note from a particular instrument is played , the card actually looks up for an equivalent collection of digital Audio Samples and reconstruct the sound with that models The resulting sounds are better than FM counterparts. This sound synthesis technology affects MIDI music much more than the digital audio files.
CREATIVE’S FAMILY OF SOUND CARDS Sound Blaster card:- 8 bit sound card- The earliest of the series-was extensively used by many of the popular CD-ROM Gaming series Sound Blaster Pro:- 8 bit sound card-had slight improvements over its predecessor like the stereo sounds. Sound Blaster 16: - 16 bit sound card-perhaps the most popular one in the creative family Sound Blaster Multi CD/SCSI:- 16 Bit sound card-with advanced signal processor and option like Wave Wave card up gradations, these two cards were compatible with CD-ROM Drives Sound Blaster AWE32:AWE32:- 16 bit sound card-A widely improved avatar of sound blaster 16 with very interesting enhancements like advanced wave effects synthesis and 3D surround sound etc Sound Blaster AWE64:AWE64:SOUND CARD FUNCTIONALITIES: 1. Audio Audio playback playback-in -inclu cludin ding g speech speech ,music ,music and MIDI MIDI 2. CD audio audio Playback-P Playback-Playi laying ng audio audio CDs CDs from CD-ROM CD-ROM 3. Adjusting Adjusting your your output speakers speakers for optimum optimum volume volume , bass, undertone undertone etc-mu etc-much ch like a tape recorder. 4. Audio amplificati amplification—for on—for direct input to the the speakers speakers 5. Recording Recording music music sources sources like tape recorder recorder and and microphon microphonee 6. Recording Recording MIDI MIDI notes directly directly from sources sources like like keyboards keyboards and synthe synthesizers sizers 7. Synth Synthes esiz izer er musi musicc creati creation on 8. Wave sound file file editing editing and adding adding audio audio special special effects effects like like reverb reverb 9. Providing Providing an interfac interfacee between the the IDE or SCSI SCSI controll controlled ed CD-ROM CD-ROM and sound sound cards 10. Providing an interface between the joystick joystick and the CD-ROMs/sound CD-ROMs/sound card..
THE TYPICAL SOUND CARD CONSTRUCTION: CREATIVE AWE32
DIAGRAM
THE AUDIO JACKS Jacks are single hole connecting interface on the audio cards. • They allow us to attach different devices to ou r card. • The variety of devices for which the connectivity extends, largely depends upon the • type of sound card. All jacks on your card can be found exclusively on the rear panel of your audio card. • AWE 32 has 4 jacks. • 1. LINE IN JACK This jack allows you to connect your tape recorder or disc player to your sound card, • mainly for recording and also for playback. 2. MICROPHONE IN JACK This jack allows you to connect your microphon e to your sound card for voice vo ice or • instruments recording. 3. LINE OUT JACK This jack allows you to bypass the card’s internal amplification system and divert the • out coming audio directly to external amplifiers/speakers. 4. SPEAKER OUT JACK This jack allows you to connect the speakers for audio o/p from the card’s built in • amplifiers.
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This built amplifier has minimum o/p power of 4 watts per channel from 4 ohm speaker and two watt per channel from8 ohm speaker.
THE CONNECTORS
1. CD AUDIO CONNECTORS This connector enables you to connect your audio card to a CD-ROM drive using the • audio cable. This connector allows audio signals to be transferred from the music CDs in your CD-ROM drive to your audio card. 2. IDE CD-ROM DATA CONNECTOR This connector allows you to connect your Audio card to an IDE controlled CD-ROM • drive using a CD-ROM data cable. This connection co nnection is a mandatory for the sound cards c ards to recognize and play pla y music in multimedia CD titles. 3. Joystick/MIDI connector This connector allows you to connect a joystick and MIDI kit, simultaneously to your • sound card. 4. MEMORY MODULE EXPANSION SLOTS This slot allows you to install memory chips on your audio card so that you have more • RAM for your MIDI instrument samples. 5. MODEM CONNECTORS This connector enables you to connect your audio card to any modem card that has got • the necessary interface. 6. PC SPEAKER CONNECTOR It enables you to redirect the sounds that normally come out of the pc speakers to your • soundcard. CONFIGURING THE SOUND CARD:
After installing the sound card and its compon ents on the computer, the system must be configured with the relevant ‘device driver ’s/w ’s/w so that other computer is able to recognize the new entrant and subsequently divert the audio signals to the sound card. DIGITAL AUDIO PLAYBACK AND EDITING AUDIO PLAYBACK Windows media Player. CREATIVE MULTIMEDIA DECS: 1. Creative CD This program allows the user to playback audio au dio CD’s from the CD-ROM drive • and hear the Play back from speakers with or without amplification from the sound card. It includes advanced options like random track selection and digital playback. • 2. Creative WAVE
This program is meant for .Wav .Wav files playback Advanced options like fine selection of track, multiple display forms, direct volume • control and several others. 3. Creative MIDI This program allows the user to playback MIDI music files. • Advanced options include multiple track selection, and touch sensitive display.. display.. • •
4. Creative Remote: A combination all above mentioned player program programs. With a single control • interface, one can control all the multimedia devices and files supported by the system.
DIGITAL DIGITAL AUDIO RECORDING PROCESS
1. Keep your microphone socket plugged in properly 2. Activate the sound Recorder from the accessories program Group 3. Verify the volume control is adjusted properly. 4. Click on the sound recorder Button 5. Start making the sound you wanted to record 6. If the recording is proper, the green line on the center of the panel pane l starts moving up and down in a zig zag manner 7. To stop the recording process 8. To hear your recording, rewind and play 9. Save
AUDIO EDITING TERMINOLOGY
1,Trimming: It is the process of removing the unwanted blank spaces 2.Splicing Splicing process refers to removal of unwanted sounds 3.Reassembling Assemble several stray pieces of audio together, to make up a single file. 4.Volume Control Increasing or decreasing the volume of either portions or whole of the recorded audio clipses 5.Time stretching matching the time with audio source 6.Resampling
Process of reducing the sound quality from 32 bit recordings to 16 bit or from 16 bit to 8 bit
CONCEPT OF MIDI
Instead of storing the actual sound samples in the form of numbers, a typical MIDI file just record the description of the ongoing ongo ing music-like the musical notes that are currently playing the note in the form of numeric data. MIDI VS DIGITAL AUDIO It be could be recalled that digital Audio files store audio data in the form of • numerical samples , that are converted back to audio form during play back.- with a whole lot of Adc and DAC convention circuitry. circuitry. MIDI stores only the audio environments and variables – not actual sounds that • are issued out of the audio source
THE GENERAL MIDI STANDARDS A)Base Level MIDI Devices: Those MIDI Devices, which are capable of playing back at least three melodic instrument track and a percussion track B)Extended Level MIDI Devices: Those MIDI Devices, which are capable of playing playing back at least nine melodic instrument track and a percussion track.
GENERAL MIDI CHANNEL ASSIGNMENTS ASSIGNMENTS
Chan Channe nels ls 1 to to 9 Channel nnelss 10 Chann Channel elss 13 to to 15 Channel nnelss 16
-Ext -Exten ende ded d lev level el melo melodi dicc ins instr trum umen ents ts with with 16 note note poly polyph phon ony y -Exte xtended le level percussion instrume uments nts with 16 no note pol polyphony -bas -basee level level Mel Melodi odicc inst instru rume ment ntss with with 6 note note pol polyp yphon hony y -Base ase leve evel Melo elodic dic Instrume uments with 3 Note polyphony hony
WORKING WITH MIDI
1.MIDI files can be played back, either by using the player program with the help of the windows Media player player program, after properly configuration the same. same. 2.Before starting the process of MIDI creation. It is better to ch eck up royalty free MIDI file libraries that are available in the market and the net. 3.To 3.To build up a MIDI music music studio, one needs to have a MIDI compatible synthesizer Electronic keyboard, MIDI plug in cables and MIDI sequencer software.
4.After the MIDI recording is over, the resulting MIDI data has to be edited to suit the specific requirements of the project. A MIDI sequencer software is used to edit MIDI files.
DIGITAL VIDEO FUNDAMENTALS : VIDEO IN MULTIMEDIA PROJECTS 1.The project has certain relevant sequences/material that can be video graphed 2.The project has certain sequences/material that can be produced with the help of computer animations 3.The project has to be made more attractive with video or 4.The project has live lectures/demonstrations/other per recorded material to be incorporated FULL MOTION VIDEO Digital Video Video files played back at a speed of 25-30 frames per second. CODEC(Compression –Decompression algorithm for video files) Some famous codec’s are *Intel- Indeo Video Video drivers *Microsoft-VFW Drivers like Microsoft Microsoft Video1,Microsoft Video1,Microsoft RLE etc *IBM- ultimation *Supermac- cinepak drivers *creative-spigot *MPEG
DIGITAL DIGITAL VIDEO PRODUCTION TECHNIQUES VIDEO PRODUCTION IN MULTIMEDIA MULTIMEDIA 1.Shooting the necessary video sequences, 2.Video capture and 3.Digital video editing SHOOTING THE SEQUENCES 1.Be sure of the video broadcast broadc ast standards you are using for the recording(NTSC AND PAL) PAL) 2.Be sure of the video recording format you you are using for recording data on your your data on your tape. 3.Be sure to maintain even lighting in shooting and maintain minimum number of colors in the scene as far as possible 4.Try to keep the camera stationary as far as possible throughout the the shooting sequence 5.Keep the light levels to the maximum. 6.Don’t make long swings or incessant position shift shift they may become difficult to to edit 7.Finally,it 7.Finally,it is far better for all real time multimedia projects to depen d on video professionals for such recording purposes. VIDEO CAPTURE TECHNIQUES
Video Video capture is the technology technolog y by which video signals are converted to digital signals and fed into the computers,to be stored as video files in some multimedia video file format Video Capture Boards Quadrants Q-Motion card SETTING UP THE DIGITAL VIDEO SYSTEM 1.A multimedia computer system with video capture card 2.A video capture software installed on the system 3.A source video-such as camcorders or video cassette recorders 4.relevant cables that provide connection between the two A TYPICAL VIDEO EDITING SOFTWARE KINETIX ANIMATOR STUDIO
FRAME MODE VERSUS TIME MODE UNDER FRAME MODE: The frame mode opens up the video sequence as individual frames UNDER TIME MODE The time mode opens up the same as a group of time bound entities CUT,COPY AND PASTE OPERATIONS ZOOMING DIGITAL PAINTING PROCESS ALTERING THE VIDEO SEQUENCE Resize and Crop