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3   multimedia elements - audio
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3 multimedia elements - audio

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3   multimedia elements - audio 3 multimedia elements - audio Presentation Transcript

  • Audio
    Sound Waves
  • Sound Formats
    There are three major groups of audio file formats:
    Uncompressed
    eg, WAV
    Lossless Compression Format
    eg, lossless Windows Media Audio (WMA).
    Lossy compression
    eg,MP3
    Vorbis
    lossy Windows Media Audio (WMA)
    AAC.
  • Lossy? Lossless?
    Lossless is a compression format where you don’t lose quality because the quality is stored for later
    Eg, Gif images, lossless WMA
    Lossy is a compression type where you do lose quality, the quality is thrown away when you compress
    Eg, JPEG images, MPEG sound/video
  • Sampling Rates for Audio Data
    Sound is analog data: it has continuous variable points
    Audio is sound which has been digitised by a computer
    Sound is converted to audio via the sound card which is a da and ad converter
  • The method used to digitise sound is called sampling
    Sampling has 3 characteristics
    Sampling rate: number of times a sample (Slice) is taken from a sound wave.
    Higher sampling rate, the better quality the sound
    Two common sampling Rates:
    44.1kHz (44100 samples per second)
    22.05kHz (22050 samples per second)
  • Sample size is the number of bits per sample (number of possible points)
    More bits= higher quality sound
    8 bit 16 bit
    Sampling Characteristics
  • Sampling Characteristics
    Mono or stereo
    Mono= one channel of sound
    Stereo= two channels of sound
    Surround Sound:
    Surround soundencompasses a range of techniques for enriching the sound reproduction quality of an audio source with audio channels reproduced via additional, discrete speakers. The three-dimensional (3D) sphere of human hearing can be virtually achieved with audio channels above and below the listener. To that end, the multichannel surround sound application encircles the audience
  • Audio file size
    Sample rate x sample size x time in seconds x channels
    Eg. 44.1kHz (44100 samples per second)
    16 bit sample
    2 mins
    Stereo
  • Audio file size
    44100 x 16 x 120 x 2=169344000 bits
    The greater the detail the greater the file size.
  • Egs
  • Audio – File Formats
    WAV
    WAVE or WAV, short for Waveform Audio File Format, is a Microsoft and IBM audio file format standard for storing an audio bit stream on PCs. It is an application of the RIFF bit stream format method for storing data in “chunks. It is the main format used on Windows systems for raw and typically uncompressed audio.
    Uncompressed WAV files are quite large in size, so, as file sharing over the Internet has become popular, the WAV format has declined in popularity. However, it is still a commonly used file type, suitable for retaining “first generation” archived files of high quality, for use on a system where disk space is not a constraint, or in applications such as audio editing, where the time involved in compressing and uncompressing data is a concern.
  • Audio – File Formats
    AIFF
    Audio Interchange File Format (AIFF) is most commonly used on Apple Macintosh computer systems. The audio data in a standard AIFF file is uncompressed pulse-code modulation (PCM). There is also a compressed variant of AIFF known as AIFF-C or AIFC, with various defined compression codec's.
    Standard AIFF is a leading format (along with SDII and WAV) used by professional-level audio and video applications, and unlike the better-known lossy MP3 format, it is non-compressed (which aids rapid streaming of multiple audio files from disk to the application), and lossless. Like any non-compressed, lossless format, it uses much more disk space than MP3—about 10MB for one minute of stereo audio at a sample rate of 44.1 kHz and a sample size of 16 bits.
  • Audio – File Formats
    MP3
    MPEG-1 Audio Layer 3, more commonly referred to as MP3, is a patented digital audio encoding format using a form of lossy data compression. It is a common audio format for consumer audio storage, as well as a de facto standard of digital audio compression for the transfer and playback of music on digital audio players.
    MP3 is an audio-specific format that was designed by the Moving Picture Experts Group as part of its MPEG-1 standard.
    The use in MP3 of a lossy compression algorithm is designed to greatly reduce the amount of data required to represent the audio recording and still sound like a faithful reproduction of the original uncompressed audio for most listeners.
    The compression works by reducing accuracy of certain parts of sound that are deemed beyond the auditory resolution ability of most people. This method is commonly referred to as perceptual coding
  • Audio – File Formats
    WMA
    Windows Media Audio (WMA) is an audio data compression technology developed by Microsoft. The name can be used to refer to its audio file format or its audio codecs. WMA consists of four distinct codecs. The original WMA codec, known simply as WMA, was conceived as a competitor to the popular MP3 and RealAudio codecs.
    WMA Pro, a newer and more advanced codec, supports multichannel and high resolution audio. A lossless codec, WMA Lossless, compresses audio data without loss of audio fidelity.
  • Audio – File Formats
    MIDI
    MIDI (Musical Instrument Digital Interface), is an industry-standard protocol defined in 1982 that enables electronic musical instruments such as keyboard controllers, computers, and other electronic equipment to communicate, control, and synchronize with each other. MIDI allows computers, synthesizers, MIDI controllers, sound cards, samplers and drum machines to control one another, and to exchange system data. MIDI does not transmit an audio signal or media — it transmits "event messages" such as the pitch and intensity of musical notes to play, control signals for parameters such as volume, vibrato and panning, cues, and clock signals to set the tempo. As an electronic protocol, it is notable for its widespread adoption throughout the music industry.
    All MIDI compatible controllers, musical instruments, and MIDI-compatible software follow the same MIDI 1.0 specification, and thus interpret any given MIDI message the same way, and so can communicate with and understand each other. Because the music is simply data rather than recorded audio waveforms, the data size of the files is quite small by comparison.