00hdddhjjcdsshkmgfffdsd72264519_Ch05.ppt
- 2. Overview ๏ฎ Introduction to sound. ๏ฎ Multimedia system sound. ๏ฎ Digital audio. ๏ฎ MIDI audio. ๏ฎ Audio file formats.
- 3. Overview ๏ฎ MIDI versus digital audio. ๏ฎ Adding sound to multimedia project. ๏ฎ Professional sound. ๏ฎ Production tips.
- 4. Introduction to Sound ๏ฎ Vibrations in the air create waves of pressure that are perceived as sound. ๏ฎ Sound waves vary in sound pressure level (amplitude) and in frequency or pitch. ๏ฎ โAcousticsโ is the branch of physics that studies sound. ๏ฎ Sound pressure levels (loudness or volume) are measured in decibels (dB). ๏ฎ A dB measurement is actually the ratio b/w a chosen reference point on a logarithmic scale and the level that is actually experienced.
- 5. Multimedia System Sound ๏ฎ System sounds are assigned to various system events such as startup and warnings, among others. ๏ฎ Macintosh provides several system sound options such as glass, indigo, laugh. ๏ฎ In Windows, available system sounds include start.wav, chimes.wav, and chord.wav. ๏ฎ Multimedia sound is either digitally recorded audio or MIDI (Musical Instrumental Digital Interface) music.
- 6. Digital Audio ๏ฎ Digital audio data is the actual representation of sound, stored in the form of samples. ๏ฎ Samples represent the amplitude (or loudness) of sound at a discrete point in time. ๏ฎ Quality of digital recording depends on the sampling rate, (or frequency) that is, the number of samples taken per second.
- 7. Digital Audio ๏ฎ The three sampling frequencies most often used in multimedia are CD-quality 44.1 kHz, 22.05 kHz and 11.025 kHz. ๏ฎ The number of bits used to describe the amplitude of sound wave when sampled, determines the sample size. ๏ฎ Digital audio is device independent. ๏ฎ The value of each sample is rounded off to the nearest integer (quantization).
- 8. ๏ฎ In signal processing, quantization refers to approximating the output by one of a discrete and finite set of values, while replacing the input by a discrete set is called discretization, and is done by sampling: the resulting sampled signal is called a discrete signal (discrete time), and need not be quantized (it can have continuous values). To produce a digital signal (discrete time and discrete values), one both samples (discrete time) and quantizes the resulting sample values (discrete values).
- 9. ๏ฎ Sampled signal (discrete signal): discrete time, continuous values
- 10. ๏ฎ Quantized signal: continuous time, discrete values
- 11. ๏ฎ Digital signal (sampled, quantized): discrete time, discrete values
- 12. Digital Audio Crucial aspects of preparing digital audio files are: ๏ฎ Balancing the need for sound quality against available RAM and hard disk resource. ๏ฎ Setting appropriate recording levels to get a high-quality and clean recording.
- 13. Digital Audio ๏ฎ Audio resolution determines the accuracy with which sound can be digitized. ๏ฎ Size of a monophonic digital recording = sampling rate x (bit resolution/8) x 1. ๏ฎ Size of stereo recording = sampling rate x duration of recording in seconds x (bit resolution/8) x 2.
- 14. Digital Audio ๏ฎ Once a recording had been completed, it almost always needs to be edited. ๏ฎ Basic sound editing operations include trimming, splicing and assembly, volume adjustments and working on multiple tracks.
- 15. Digital Audio ๏ฎ Additional available sound editing operations include format conversion, resampling or downsampling, fade-ins and fade-outs, equalization, time stretching, digital signal processing, and reversing sounds.
- 16. MIDI Audio ๏ฎ MIDI is a shorthand representation of music stored in numeric form. ๏ฎ It is not digitized sound. ๏ฎ A sequencer software and sound synthesizer is required in order to create MIDI scores. ๏ฎ MIDI is device dependent.
- 17. MIDI Audio ๏ฎ Since they are small, MIDI files embedded in web pages load and play promptly. ๏ฎ Length of a MIDI file can be changed without affecting the pitch of the music or degrading audio quality. ๏ฎ Working with MIDI requires knowledge of music theory.
- 18. Audio File Formats ๏ฎ A sound fileโs format is a recognized methodology for organizing data bits of digitized sound into a data file. ๏ฎ On the Macintosh, digitized sounds may be stored as data files, resources, or applications such as AIFF or AIFC. ๏ฎ In Windows, digitized sounds are usually stored as WAV files.
- 19. Audio File Formats ๏ฎ CD-ROM/XA (Extended Architecture) format enabled several recording sessions to be placed on a single CD-R (recordable) disc. ๏ฎ Linear Pulse Code Modulation is used for Red Book Audio data files on consumer-grade music CDs.
- 20. MIDI Versus Digital Audio ๏ฎ MIDI is analogous to structured or vector graphics, while digitized audio is analogous to bitmapped images. ๏ฎ MIDI is device dependent while digitized audio is device independent. ๏ฎ MIDI files are much smaller than digitized audio. ๏ฎ MIDI files sound better than digital audio files when played on a high-quality MIDI device.
- 21. ๏ฎ With MIDI, it is difficult to playback spoken dialog, while digitized audio can do so with ease. ๏ฎ MIDI does not have consistent playback quality while digital audio provides consistent playback quality. ๏ฎ One requires knowledge of music theory in order to run MIDI, while digital audio does not have this requirement. MIDI Versus Digital Audio
- 22. Adding Sound to Multimedia Project ๏ฎ File formats compatible with multimedia authoring software being used along with delivery mediums, must be determined. ๏ฎ Sound playback capabilities offered by end userโs system must be studied.
- 23. Adding Sound to Multimedia Project ๏ฎ The type of sound, whether background music, special sound effects, or spoken dialog, must be decided. ๏ฎ Digital audio or MIDI data should be selected on the basis of the location and time of use.
- 24. Professional Sound ๏ฎ Red Book (or ISO 10149) standard is a standard for digitally encoding high-quality stereo. ๏ฎ For this standard, the digital audio sample size is 16 bits and sampling rate is 44.1 KHz. ๏ฎ The amount of digital sound information required for high- quality sound takes up a great deal of disk storage space.
- 25. Professional Sound ๏ฎ Compression techniques reduce space but reliability suffers. ๏ฎ Space can be conserved by downsampling or reducing the number of sample slices taken per second. ๏ฎ File size of digital recording (in bytes) = sampling rate X duration of recording (in secs) X (bit resolution/8) X number of tracks.
- 26. Production Tips ๏ฎ Recording on inexpensive media rather than directly to disk prevents the hard disk from being overloaded with unnecessary data. ๏ฎ The equipment and standards used for the project must be in accordance with the requirements.
- 27. Production Tips ๏ฎ It is vital to maintain a high-quality database that stores the original sound material. ๏ฎ Sound and image synchronization must be tested at regular intervals.
- 28. Production Tips ๏ฎ The speed at which most animations and computer-based videos play, depends on the userโs CPU. ๏ฎ Soundโs RAM requirements as well as the usersโ playback setup must be evaluated. ๏ฎ Copyrighted material should not be recorded or used without securing appropriate rights from owner or publisher.
- 29. Summary ๏ฎ Vibrations in air create waves of pressure that are perceived as sound. ๏ฎ Multimedia system sound is digitally recorded audio or MIDI (Musical Instrumental Digital Interface) music. ๏ฎ Digital audio data is the actual representation of a sound, stored in the form of samples.
- 30. Summary ๏ฎ MIDI is a shorthand representation of music stored in numeric form. ๏ฎ Digital audio provides consistent playback quality. ๏ฎ MIDI files are much smaller than digitized audio. ๏ฎ MIDI files sound better than digital audio files when played on high-quality MIDI device.