1. A stereo audio file 1. Audio Channels Number of audio channels determines number of waveforms in a recording Two relevant types of recording Stereo recording Contains two audio channels Offers richer listening experience Mono recording Contains one audio channel Requires half the amount of storage space for stereo recording A mono audio file

2. 2. Audio File Formats Common Audio File Formats Audio file formatFile extension Wave Format.wav MIDI Format.mid MPEG Audio Format.mp3 Windows Media Audio.wma RealAudio/RealMedia.ra /.rm Advanced Audio Coding.mp4 /.m4a

3. 2 Audio File Formats Wave Format (WAV) Native audio format in Microsoft Windows Gives the best audio quality but has the largest audio file size For example, the file size of four-minute CD-quality stereo recording 40.37 MB Huge file size, not suitable to use on the Web

4. 2 Audio File Formats Wave Format (WAV) zooming A visual presentation of an audio wave

5. 4.2 Audio File Formats MP3 MPEG-1 Audio Layer-3 (MP3) Popular standard for audio compression Supports small file size and high sound quality Compresses storage space by removing inaudible differences in sound signals

6. 2 Audio File Formats MP3 Bit rate Determines the audio quality and file size In general, higher bit rate → better audio quality QualityEncoding bit rateFile size CD128 kbps2.95 MB FM radio64 kbps1.47 MB Audio quality vs file size for an MP3 file storing a 3-minte song

7. 2 Audio File Formats MP3 Streaming A technology in which the downloaded portion of an audio file can be played immediately MP3 supports streaming Playing MP3 with Windows Media Player MP3 playing software Mobile MP3 players

8. 2 Audio File Formats Windows Media Audio (WMA, ASX) A compressed streaming audio format developed by Microsoft The next most popular format after MP3 WMA – a popular format for online radio live broadcast

9. 4.2 Audio File Formats RealAudio/RealMedia (RA/RM) A streaming audio format developed by RealNetworks RealPlayer Playing RA/RM requires audio decompression software Example RealPlayer Can be downloaded from http://www.real.com http://www.real.com

10. 2 Audio File Formats Advanced Audio Coding (AAC) a lossy compressed streaming audio format developed by MPEG The most advanced audio format on the Internet Supposed to be the successor to MP3 The Apple’s iPod music player supports AAC format