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Audio Compression: Understanding Formats & Compression Techniques

Learn about common digital audio formats, compression techniques, and the differences between compressed and uncompressed file formats. Explore the categories of audio compression – lossless and lossy – and understand the impact on audio quality. Discover the reasons for compressing audio files and how to adjust settings for compressed audio files to achieve the desired quality and size.

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Audio Compression: Understanding Formats & Compression Techniques

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  1. Understanding A/V terms and formats Online Media Session 2

  2. Today's Session • Common digital audio and video formats • Compression • Non – Compression • Bit Rates • Compressing audio/music for the web

  3. Common Digital Audio Formats • AIFF (Mac) • ACC (Mac) • CD audio (CCDA) • MP3 • Windows Media – Audio • QuickTime • RealAudio • Wav

  4. Different file formats • Allow for different file sizes and qualities. All audio files have the following attributes.. • File format • Data rate (I.e compression) • Channels (mono, stereo, or multi-channel) • Sample rate quality • Bit depth quality • Compressed or uncompressed format

  5. Compressed and uncompressed formats It is possible to divide digital audio file formats into 2 categories ... • Uncompressed. Example include ... CD audio, DV audio, Flac, .aif and .wav files. • Compressed. Examples include ... MP3, Real Audio, Dolby AC3 (DVD video)

  6. The two "categories" of audio compression • Lossless. This is a process whereby clever algorithms (such asFLAC ) are employed to "compact" the data in a file without losing any information. Lossless compression can reduce the file size but no-where near as much as lossy. • Lossy. These codecs find ways to throw away information in the file which it thinks the majority of listeners ears won't miss. File size reduction can be dramatic (10 times smaller) but the effect on audio quality is usually noticeable. • This section will focus on lossy compressions because it is by far the most used form of audio file reduction technology (iPod, Mobile phones, DVD, Freeview, Cable TV etc).

  7. Why compress audio files? • Audio compression is employed for 3 primary reasons ... • to reduce file size so that more audio may be stored on a given media format (MP3 players, DVD-video discs, MiniDiscs etc) • to reduce file size so that files will download from a web site faster • to reduce Data Rate so that files will stream (broadcast) over a network such as the internet

  8. Compressed audio file settings • Compressed audio files can vary in size and quality depending on these primary settings ... • Sample Rate • Number of channels - stereo, mono, surround sound or multi-channel • Choice of audio compression codec • Audio compression codec settings

  9. Compressed audio file settings • By altering these settings, either before or after recording, you can achieve differing ... • Date Rates • Files sizes • Audio quality

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