Audio
Content
4.1 Different Audio Attributes Sampling Rate and Sample Size
Sampling is the process of converting sounds from analogue to digital The quality of digitized sounds is determined by: Sample Sample size size • The amount of Sampling Sampling rate rate
• The number of capture points used to record one-second analogue audio • Measured in Hertz (Hz) • Common sampling rates: 8 kHz, 11.025 kHz, 22.05 kHz, 44.1 kHz • Measured in bits • Common sample sizes: 8-bit, 16-bit
information used to record an audio sample
4.1 Different Audio Attributes Sampling Rate and Sample Size
Effect of Sampling Rate on Sample Waveform
Higher sampling rate → greater similarity between the sample waveform and the original one → higher quality
Sampling rate/Sample size 44.1 kHz / 16-bit 22.05 kHz / 8-bit 11.025 kHz / 8-bit
Sound quality CD FM radio AM radio
Common sampling rate and sample size combination
4.1 Different Audio Attributes Audio Channels
Number of audio channels determines number of waveforms in a recording Two relevant types of recording Mono recording
• Contains one audio channel • Requires half the amount of storage space for stereo recording
Stereo recording
• Contains two audio channels • Offers richer listening experience
A stereo audio file A mono audio file
4.1 Different Audio Attributes Audio File Size
Uncompressed file size can be estimated by,
Number Audio file size Sample Sampling × × of audio × Time = (uncompressed) size rate channels
For example, the uncompressed file size of a ten-second stereo recording at a sampling rate of 44.1 kHz and 16-bit sample size should be: 44,100 Hz × 16 bits × 2 × 10s =14,112,000 bits =1,764,000 bytes =1.68 MB
4.1 Different Audio Attributes Audio File Size
Uncompressed file size can be estimated by,
Number Audio file size Sample Sampling × × of audio × Time = (uncompressed) size rate channels
For example, the uncompressed file size of a ten-second stereo recording at a sampling rate of 44.1 kHz and 16-bit sample size should be: 44,100 Hz × 16 bits × 2 × 10s =14,112,000 bits =1,764,000 bytes =1.68 MB
4.2 Audio File Formats Common Audio File Formats
Audio file format Wave Format MIDI Format MPEG Audio Format Windows Media Audio RealAudio/RealMedia Advanced Audio Coding File extension
.wav .mid .mp3 .wma .ra /.rm .mp4 /.m4a
4.2 Audio File Formats Wave Format (WAV)
Native audio format in Microsoft Windows Supports various sampling rates, sample sizes and audio channels Gives the best audio quality but has the largest audio file size For example, the file size of four-minute CD-quality stereo recording 44,100 Hz × 16 bits × 2 × (4 × 60s) =338,688,000 bits =42,336,000 bytes =40.37 MB
Huge file size, not suitable to use on the Web
4.2 Audio File Formats Wave Format (WAV)
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A visual presentation of an audio wave
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4.2 Audio File Formats MIDI Format (MID)
Stands for Musical Instrument Digital Interface Stores music in the form of digital musical instructions instead of a set of capture points of analogue music Each instruction represents the volume, frequency and duration of a sound a specific musical instrument emits No analogue audio can be recorded in a MIDI file
4.2 Audio File Formats MIDI Format (MID)
A midi instruction
A MIDI file displayed in MIDI editing software (left). The MIDI instructions (represented as horizontal green bars), which contain information of digital sounds, are played sequentially from left to right. This concept is very similar to some specially designed music box, in which analogue music instructions are played sequentially (right).
4.2 Audio File Formats MIDI Format (MID)
File size Hundreds of times smaller than that of a WAV file Typically less than 100 KB Comparison of a WAV file and a MIDI file
WAV file Nature Describe sound through sampling Generally very large More difficult to edit Long because of the large file size MIDI file Describe sound through MIDI code and instructions Much smaller Allow more precise editing Short
File size Ease of editing Loading time
4.2 Audio File Formats MIDI Format (MID)
Most sound cards provide a MIDI interface for connecting external MIDI devices (e.g. MIDI keyboards) to a computer
MIDI keyboard records keystrokes
MIDI software converts keystroke sequence to MIDI instructions
4.2 Audio File Formats MP3 and Lossy Compression
MPEG-1 Audio Layer-3 (MP3) Popular standard for lossy audio compression Supports small file size and high sound quality Compresses storage space by removing inaudible differences in sound signals
4.2 Audio File Formats MP3 and Lossy Compression
Bit rate Determines the audio quality and file size Specifies the amount of data (in kilobit per second, kbps) used for representing the compressed audio In general, higher bit rate → better audio quality
Quality CD Quasi-CD FM radio AM radio Encoding bit rate 128 kbps 96 kbps 64 kbps 32 kbps File size 2.95 MB 2.21 MB 1.47 MB 757 KB
Audio quality vs file size for an MP3 file storing a 3-minte song
4.2 Audio File Formats MP3 and Lossy Compression
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 Extracting MP3 with Extraction software (or CD ripper)
4.2 Audio File Formats MP3 and Lossy Compression
Winamp – popular MP3 playing software
Windows Media Player can extract music stored on an audio CD
4.2 Audio File Formats Windows Media Audio (WMA, ASX)
A compressed streaming audio format developed by Microsoft Supports both lossless and lossy compression The next most popular format after MP3
Music extraction – WMA supports both lossy and lossless compression
WMA – a popular format for online radio live broadcast
4.2 Audio File Formats RealAudio/RealMedia (RA/RM)
A streaming audio format developed by RealNetworks Supports lossy compression only Playing RA/RM requires proprietary audio decompression software Example RealPlayer Can be downloaded from
RealPlayer
http://www.real.com
4.2 Audio File Formats RealAudio/RealMedia (RA/RM)
Specialised RA encoding software usually provides different bit-rate options to cater for different Internet connection speeds Lower bit rate → smaller file size → lower quality of output audio Example RealProducer Can be downloaded from
RealPlayer
http://www.realne tworks.com/produ cts/producer/basic .html
4.2 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
4.2 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
Sampling is the process of converting sounds from analogue to digital The quality of digitized sounds is determined by: Sample Sample size size • The amount of Sampling Sampling rate rate
• The number of capture points used to record one-second analogue audio • Measured in Hertz (Hz) • Common sampling rates: 8 kHz, 11.025 kHz, 22.05 kHz, 44.1 kHz • Measured in bits • Common sample sizes: 8-bit, 16-bit
information used to record an audio sample
4.1 Different Audio Attributes Sampling Rate and Sample Size
Effect of Sampling Rate on Sample Waveform
Higher sampling rate → greater similarity between the sample waveform and the original one → higher quality
Sampling rate/Sample size 44.1 kHz / 16-bit 22.05 kHz / 8-bit 11.025 kHz / 8-bit
Sound quality CD FM radio AM radio
Common sampling rate and sample size combination
4.1 Different Audio Attributes Audio Channels
Number of audio channels determines number of waveforms in a recording Two relevant types of recording Mono recording
• Contains one audio channel • Requires half the amount of storage space for stereo recording
Stereo recording
• Contains two audio channels • Offers richer listening experience
A stereo audio file A mono audio file
4.1 Different Audio Attributes Audio File Size
Uncompressed file size can be estimated by,
Number Audio file size Sample Sampling × × of audio × Time = (uncompressed) size rate channels
For example, the uncompressed file size of a ten-second stereo recording at a sampling rate of 44.1 kHz and 16-bit sample size should be: 44,100 Hz × 16 bits × 2 × 10s =14,112,000 bits =1,764,000 bytes =1.68 MB
4.1 Different Audio Attributes Audio File Size
Uncompressed file size can be estimated by,
Number Audio file size Sample Sampling × × of audio × Time = (uncompressed) size rate channels
For example, the uncompressed file size of a ten-second stereo recording at a sampling rate of 44.1 kHz and 16-bit sample size should be: 44,100 Hz × 16 bits × 2 × 10s =14,112,000 bits =1,764,000 bytes =1.68 MB
4.2 Audio File Formats Common Audio File Formats
Audio file format Wave Format MIDI Format MPEG Audio Format Windows Media Audio RealAudio/RealMedia Advanced Audio Coding File extension
.wav .mid .mp3 .wma .ra /.rm .mp4 /.m4a
4.2 Audio File Formats Wave Format (WAV)
Native audio format in Microsoft Windows Supports various sampling rates, sample sizes and audio channels Gives the best audio quality but has the largest audio file size For example, the file size of four-minute CD-quality stereo recording 44,100 Hz × 16 bits × 2 × (4 × 60s) =338,688,000 bits =42,336,000 bytes =40.37 MB
Huge file size, not suitable to use on the Web
4.2 Audio File Formats Wave Format (WAV)
zoo
mi
ng
A visual presentation of an audio wave
zoo
ng i m
4.2 Audio File Formats MIDI Format (MID)
Stands for Musical Instrument Digital Interface Stores music in the form of digital musical instructions instead of a set of capture points of analogue music Each instruction represents the volume, frequency and duration of a sound a specific musical instrument emits No analogue audio can be recorded in a MIDI file
4.2 Audio File Formats MIDI Format (MID)
A midi instruction
A MIDI file displayed in MIDI editing software (left). The MIDI instructions (represented as horizontal green bars), which contain information of digital sounds, are played sequentially from left to right. This concept is very similar to some specially designed music box, in which analogue music instructions are played sequentially (right).
4.2 Audio File Formats MIDI Format (MID)
File size Hundreds of times smaller than that of a WAV file Typically less than 100 KB Comparison of a WAV file and a MIDI file
WAV file Nature Describe sound through sampling Generally very large More difficult to edit Long because of the large file size MIDI file Describe sound through MIDI code and instructions Much smaller Allow more precise editing Short
File size Ease of editing Loading time
4.2 Audio File Formats MIDI Format (MID)
Most sound cards provide a MIDI interface for connecting external MIDI devices (e.g. MIDI keyboards) to a computer
MIDI keyboard records keystrokes
MIDI software converts keystroke sequence to MIDI instructions
4.2 Audio File Formats MP3 and Lossy Compression
MPEG-1 Audio Layer-3 (MP3) Popular standard for lossy audio compression Supports small file size and high sound quality Compresses storage space by removing inaudible differences in sound signals
4.2 Audio File Formats MP3 and Lossy Compression
Bit rate Determines the audio quality and file size Specifies the amount of data (in kilobit per second, kbps) used for representing the compressed audio In general, higher bit rate → better audio quality
Quality CD Quasi-CD FM radio AM radio Encoding bit rate 128 kbps 96 kbps 64 kbps 32 kbps File size 2.95 MB 2.21 MB 1.47 MB 757 KB
Audio quality vs file size for an MP3 file storing a 3-minte song
4.2 Audio File Formats MP3 and Lossy Compression
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 Extracting MP3 with Extraction software (or CD ripper)
4.2 Audio File Formats MP3 and Lossy Compression
Winamp – popular MP3 playing software
Windows Media Player can extract music stored on an audio CD
4.2 Audio File Formats Windows Media Audio (WMA, ASX)
A compressed streaming audio format developed by Microsoft Supports both lossless and lossy compression The next most popular format after MP3
Music extraction – WMA supports both lossy and lossless compression
WMA – a popular format for online radio live broadcast
4.2 Audio File Formats RealAudio/RealMedia (RA/RM)
A streaming audio format developed by RealNetworks Supports lossy compression only Playing RA/RM requires proprietary audio decompression software Example RealPlayer Can be downloaded from
RealPlayer
http://www.real.com
4.2 Audio File Formats RealAudio/RealMedia (RA/RM)
Specialised RA encoding software usually provides different bit-rate options to cater for different Internet connection speeds Lower bit rate → smaller file size → lower quality of output audio Example RealProducer Can be downloaded from
RealPlayer
http://www.realne tworks.com/produ cts/producer/basic .html
4.2 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
4.2 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
