Task summaryWhat you will learn:
Identify different formats for sound files Understand that reducing file size will affect sound quality Understand the difference between lossy and lossless data compression How you will be assessed: Short written assessment |
Key terminologyUncompressed:
A digital file that is stored without any attempt to make it smaller. Lossy compression: A method of reducing the size of a file in a way that reduces the quality of the file's contents. Lossless compression: A method of reducing the size of a file in a way that does not reduce the quality of the file's contents. |
Activities
Lossy compression
Each sample sound is stored as a binary number, usually either 16 or 32 bits. 192,000 bytes are needed for each second of music if 16 bits are used a sample rate of 96,000 kHz - a 1 minute song would be around 11MB. If the song was in stereo, using two channels it would be twice the size at 22MB.
WAV files store uncompressed sound files in this form. Too big for everyday use. If a sound file can be made smaller then it can be downloaded more quickly and more songs can be stored on a mobile device. The most common method to compress a sound file is to use the MP3 file format. MP3s use a lossy compression to reduce the file size.
Activity 1: Compress a .WAV file to .MP3
Lossless compression - reduces the file size of a sound file without reducing the sound quality. Algorithms used to create zip files are the most common forms of lossless compression. While this is not often used for sound files, it is a good way to reduce the size of one or more files. A "zip" file ends in .zip and is smaller than the original file. Some files shrink more than others when they are compressed as zip files, but they never lose quality. The downside is that lossless compression does not reduce the file size as much as it does with lossy compression.
Activity 2: Compress the .WAV file using a compression utility
Each sample sound is stored as a binary number, usually either 16 or 32 bits. 192,000 bytes are needed for each second of music if 16 bits are used a sample rate of 96,000 kHz - a 1 minute song would be around 11MB. If the song was in stereo, using two channels it would be twice the size at 22MB.
WAV files store uncompressed sound files in this form. Too big for everyday use. If a sound file can be made smaller then it can be downloaded more quickly and more songs can be stored on a mobile device. The most common method to compress a sound file is to use the MP3 file format. MP3s use a lossy compression to reduce the file size.
Activity 1: Compress a .WAV file to .MP3
- Download the this .WAV file you may also need this library file for Audacity to complete the exercise.
- Look at the size of the .WAV file - make a note of it.
- Open Audacity and load the .WAV file you just downloaded.
- Export the .WAV file to a .MPEG format and experiment with the quality and bit rates.
- What do you notice about the file size, is there any difference in quality?
Lossless compression - reduces the file size of a sound file without reducing the sound quality. Algorithms used to create zip files are the most common forms of lossless compression. While this is not often used for sound files, it is a good way to reduce the size of one or more files. A "zip" file ends in .zip and is smaller than the original file. Some files shrink more than others when they are compressed as zip files, but they never lose quality. The downside is that lossless compression does not reduce the file size as much as it does with lossy compression.
Activity 2: Compress the .WAV file using a compression utility
- Use the same .WAV file you downloaded earlier.
- View the file in Windows Explorer and then right click on it to show the shortcut menu.
- Select the "Send to" option and choose "Compressed (zipped) folder"
- Look at the file size, what do you notice?
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Watch this video for an explanation of lossy and lossless compression.
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Assessment Task
- Answer the following assessment and submit your answers via the task set by your teacher on Dash.
- Going for Platinum Award? Submit your GarageBand track via Dash.