Audio compression

Skills: Audacity compression

IT concepts: quality-file size trade off, capture-edit-compress, lossy versus lossless compression

This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 License.

Where does this topic fit?

• Internet concepts– Applications– Technology– Implications

• Internet skills– Application development– Content creation (audio)

All data types are compressible

Image

Text

Numeric

Audio

Video

Bit Depth Sample Rate 1 minute 3 minutes

16 44,100 10.1 Mb 30.3 Mb

16 48,000 11.0 Mb 33 Mb

24 96,000 33.0 Mb 99 Mb

MP3 File 128 k/bit rate 0.94 Mb 2.82 Mb

Examples of files sizes for stereo recordings

MP 3 is a compressed format.

1. click to play

2. click to play

Which sounds best? Worst?

Audio fileFile size(Kbytes)

Bit rate(Kbits/s)

Play low quality (.mp3) 16 16

Play original (.wav) 676 688

1. play2. play3. play4. play5. play

Which sounds best? Worst?

No. Data rate File type File size

1 320 kbps .mp3 112 kB

2 Original .wav 233 kB

3 64 kbps .mp3 26 kB

4 16 kbps .mp3 10 kB

5 128 kbps .mp3 47 kB

Record and edit at high quality

Export > Save as MP3 > click Options

Compress for distribution

Variable bit rate

Bit rate Quality

8 kbps telephone

16 kbps shortwave radio

32 kbps AM radio

64 kbps FM radio

96 kbps near CD

128 kbps CD

Quality rules of thumb

Lossy compression

Information is lost– the original cannot be recovered

Audio compression

Skills: Audacity compression

IT concepts: quality-file size trade off, capture-edit-compress, lossy versus lossless compression

This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 License.

How many bytes in a three minute, CD quality song?

How many bytes in a three minute telephone quality conversation?

What is the final step in audio, image and video processing?

A few questions

Image

Text

Numeric

Audio

Video

Which data type(s) is/are suited to lossless compression? Lossy compression? Why?