MP3 files are good examples of analog-to-digital conversion. Itis simple to take an analog signal—such as your voice—and convertit into a digital file for transmission or playback. In thisactivity, we will show you how to record your voice and see howdifferent levels of digital quality affect the sound.

First, you need to download a sound editor and MP3 converter.One very good sound editor is Audacity—and it’s free. Go toaudacity.sourceforge.net and download and install the audacitysoftware. You will also need the plug-in called LAME (an MP3encoder), which is also free and available atlame.sourceforge.net.

Use Audacity to record music or your voice (you can use a cheapmicrophone). Audacity records in very high quality, but willproduce MP3 files in whatever quality level you choose.

Once you have the file recorded, you can edit the Preferences tochange the File Format to use in saving the MP3 file. Audacity/LAMEoffers a wide range of qualities. Try recording at least threedifferent quality levels. For example, for high quality, you coulduse 320 Kbps, which means the recording uses 320 Kbps of data persecond. In other words, the number of samples per second times thenumber of bits per sample equals 320 Kbps. For regular quality, youcould use 128 Kbps. For low quality, you could use 16 Kbps.

Create each of these files and listen to them to hear thedifferences in quality produced by the quantizing error. Thedifferences should be most noticeable for music. A recording at 24Kbps is often adequate for voice, but music will require a betterquality encoding.

Deliverable

1. Produce three MP3 files of the same music or voice recording atthree different quality levels.
2. List the size of each file.
3. Listen to each file and describe the quality differences youhear (if any).