Digital Audio in Multimedia
- 1. Digital Audio BY K.LALITHAMBIGA, II –Msc (CS&IT ), Department of CS&IT, NS College of Arts and Science, Theni.
- 2. Synopsis Introduction Characteristics of sound and digital audio Digital Audio System MIDI Audio File Formats Using Audio in Multimedia Applications Audio
- 3. Digital Audio SOUND ◦ Sound is simply waves of compressed air that move out from its source, similar to dropping a stone in water. ◦ Your ears are sensitive to these compressed waves. As the sound waves interact with your ear drum, the signal is sent to your brain, converting them to the sounds that you recognize. Two types of Sounds Analog sound(recorded &reproduce the signals) Digital sound(stored as numerical data & easily reproduced & manipulated)
- 4. Characteristics of Sound & Digital Audio Sound is based on two things: Energy & Transport medium. Energy from a banging drum is converted into pressure that is transmitted by the air. There are two characteristic of sound waves ◦ Amplitude ◦ Amplitude is the power or intensity of the sound. ◦ The louder the sound, the larger the amplitude. ◦ Frequency ◦ Frequency is the rate at which sound is measured. ◦ It is measured in cycles per second or Hertz(Hz).
- 5. Voice and Music The Three classes of sounds: Voices, Music and Sound effects. Voice is defined as talking, not singing by human. It is does not have a pitch and tone. Music can have rapid changes in tone and pitch. It is usually recorded and played in stereo. Sound effects can be voice or music. It is vary in tone, pitch and time.
- 6. Digitizing Sound Digitizing Sound means capturing the sound amplitude at a specific frequency. The three characteristics for recording sound: Frequency rate Amplitude measurement Sound channels (Monaural or stereo) For multimedia computers, standard frequency rates includes 11.025 Kilohertz(KHz) 22.5 KHz 44.1 KHz ◦ Amplitude measurement is based on 8 bits(1byte) for 256 levels and 16 bits for 65,536 levels
- 7. Calculating Audio Data Size There are three characteristic is used to calculating audio file sizes, amplitude, sound channels and frequency rates c=number of channels(mono-1channel, stereo- 2channel) s=sampling rate in Hertz(cycle per second) t=a time(second) b=bytes(1for 8 bits, 2 for 16 bits) File size=c*s*t*b
- 8. Digital Audio System Digital audios created when the characteristic of sound wave is represent using number – a process referred to as Digitizing. We can digitize any sound(Microphone, Synthesizer…) Digitized sound is sampled sound Every nth fraction of a second, a sample of a sound is taken & stored as digital information in bits and bytes. The quality of digital recording depends on the how often the samples are taken i.e. Higher the sampling rate better is the quality of sound.
- 9. sampling rates are normally used in multimedia 44.1KHz(CD- Quality),22.05 KHz and 11.025KHz Larger the sample size, more accurate data will describe the recorded sound The value of each sample is rounded off to the nearest integer called Quantization. Digital Audio software support Playback Record Stop Fast forward Reverse Rewind
- 10. Editing Digital Audio Trimming the clip & Splicing and Assembly
- 11. Volume adjustment & Format Conversion
- 12. Resampling or down sampling & Fade-ins & fade-out
- 14. Digital Signal Processing & Reversing sounds
- 15. Sound Controls Multimedia computes usually have software that acts as a control for the computer’s sound playback and recording. This software includes: ◦ Selection of components(Microphones, Speakers, Line-in, Line-out) ◦ Volume level, both monaural and stereo ◦ Recording input level ◦ Bass and treble controls These controls are usually accessible for a user from the operating system of the computers as well as from within multimedia products themselves
- 16. MIDI(Musical Instrument Digital Interface) It is a communications standard developed in the 1980’s for electronic instruments and computers It allows instruments from different manufactures to communicate But MIDI data is not digitized, its only music data stored in numeric form. Digital Audio is recorded where as MIDI is a score Device Independent This file is a list of time stamped commands that are recordings of musical actions
- 17. Using MIDI, we can easily and quickly compose our own original score The process of creating MIDI is quite different from digitizing a recorded audio Digitized Audio – Bitmap Image the MIDI –Vector graphics For digitized audio we simple need to play the recording through a computer device that can digitally record the sound ◦ To make MIDI, we need Notation software Sequencer software Synthesizer MIDI Keyboard
- 18. MIDI vs. Digital Audio Advantages MIDI files are more compact that audio files MIDI is small, can be easily embedded into the web pages MIDI sound source is high quality, this sounds better than audio files MIDI data is completely editable MIDI data can be easily converted to musical notations and vise versa.
- 19. Audio File Format A sound files format is a recognized methodology for compressing data bits of digitized sound into a data file The structure of the file must be known even before the data can be saved or later loaded into a computer to be edited or played as sound The file name extension identifies the method of storage used On the Macintosh, digitized sounds may be stored as data files, resources, or applications such as AIFF or AIFC In Windows, digitized sounds are usually stored as WAV files Both can use MIDI files(.mid)
- 20. Audio File Format The method used for consumer grade music CD’s is Linear Pulse Code modulation(LPCM shortened to PCM) CD-ROM/XA (Extended Architecture) format for reading and writing CD’s was developed later so one can put several recording sessions of music to be placed on a single CD-R LPCM tracks from an Audio CD are usually converted and stored on a computer in uncompressed AIFF or WAV format ◦ AIFF-Audio Interchange File Format Both contain ◦ WAV-Wave Format Uncompressed data
- 21. Audio File Format There are huge no of file formats & “Multimedia Containers” that store sound data There are converter to read & write sound files from one format to another MP3 was developed by MPEG (Moving Picture Expert Group) Common method for storing consumer audio Contains lossy compression algorithm to save space Evolved in early 1990’s WMA(Windows Media Audio) is a proprietary format OGG was developed as an open-source and royalty free ”Container” for sound compressed using the “ Vorbis algorithm” Vorbis sound data resides within an OGG container – OGG Vorbis
- 22. MP$ format is based on Apple’s Quick Time Movies (.mov) “container” model It is similar to the MOV format that stores different types of media MP4 extension is used when file streams audio & video together M4a extension is used only when file contains only audio data M4p extension contains only audio, but encrypted for Digital Rights Management(DRM) M4r files are used for ringtones on Apple’s iPhone ◦ Other GSM phones use 3gp file format for ring tones
- 23. Advanced Audio Coding(AAC) format is adopted by Apple’s iTunes store Default format for iPod, iPhone, PlayStation, Wii, Dsi, Motorala, Nokia, Philips, Samsung, Siemens and Sony Ericssion Codec is a software that compresses a stream of audio or video for data storage or transmission and then decompresses it for play back Some are “lossy” – trade quality for reduced file size transmission speed Some are “lossless” – original data is not at all altered.
- 24. Using Audio In Multimedia Application Audio Adding sound to Multimedia project & the Following Step: Determine the file formats that are compatible with MM authoring S/W Determine the sound playback capabilities that the end user’s system offers Decide the type of sound needed Decide where and when you want to use the digital audio or MIDI data Acquire source material by creating it from scratch or buying it Edit the sounds to fit your project Test the sounds to be sure they are timed properly with the project’s images.(This may involve steps 1-4 until everything is in sync)
- 25. Space Considerations Large amount of digital information is required for high quality sound, which in turn requires large amount of space. If monaural sound is adequate then one can cut the storage space by half or get double the playing time in the same memory space. With compression codec's we can reduce the size to 1/8th the space but there is loss of quality & we can also downsample. Formula ◦ Sampling rate* bits per sample/8=bytes/sec ◦ Sample rate* sample size/8 *#sec*2 (if stereo)= file size in KB
- 26. Audio Recording If we require CD quality recording, then digitize sound at 44.1KHz and 16 bit to store, at a sound studio. If we decide to do it our self then we need to invest in: ◦ Acoustically treated room ◦ High end amplifiers ◦ Recording equipments ◦ Powerful microphones Digital Audio Tape(DAT)systems provide a tape based 44.1KHz and 16 bit record an record playback capability DAT recordings are too accurate, precisely recording glitches, background noises, microphone pops, including coughs in the next room.
- 27. Audio Recording A good editor can reduce the impact of these noises but at the cost of time & money Mobile phones can record audio. USB, Flash memory recorders can be used to record and the recordings can be downloaded directly as digital files using USB cables or Card readers Audio CD’s – the method for digitally encoding the high quality stereo of the consumer CD market is an international standard, ISO 10149. Also known as “Red Book Audio” Standard Converter & burning s/w’s such as Toast & CD creator from Roxio can translate digital files of RBA found on CD directly to digital sound file formats like MP3 & WAV.
- 28. Sound For Mobile Ringtones are normally associated with phones Telephone system – Pulsating at 90 volt – signal is sent to copper wire to energize the hammer like klangs a bell But in the present systems, the mobile’s s/w takes the charge when come one calls, depending on the programmed options, plays the users choice of ringtone Ringtones play on very small speakers & often compete in a noisy environment The other tones include answer tones, sing tones, true tones, real tones, video tones & ringels