Sound File Formats

Computer sound files come in several formats, but they can be divided into two broad categories: WAV and MIDI.

• WAV: This can refer to a specific file format that has a .wav extension, but it can also refer generically to any sound file that has an analog origin. For example, when you record sound using a microphone, the resulting file is a WAV file in a generic sense of the word because it was originally a "sound wave" that the microphone captured. The tracks on an audio CD can also be considered WAV files because at some point, presumably, a person went to a recording studio and made music with their voice or with instruments that were recorded. Similarly, the very popular MP3 music format is a WAV format. Other WAV formats include RMI, AU, AIF, and AIFC. WAV files sound very realistic because they are recordings of real-life sounds. The drawback is that the file size is typically large. MP3 is a relatively compact format, but even MP3 files require about 1MB per minute of recording.

• MIDI: MIDI stands for multi-instrument digital interface, and refers to the interface between a computer and a digital instrument such as an electronic keyboard. When you make a MIDI recording, there is no analog source-it is purely digital. For example, you press a key on an electronic keyboard, and that key press is translated into instructions that are written to a computer file. No microphone, and no sound waves in the air. What is the sound of one key pressing? It is completely up to the software. It could sound like a piano, a saxophone, or a harpsichord-whatever instrument it is set up to "be" at the moment. MIDI files (usually identified by a .mid extension) are smaller in size than WAV files, and several minutes of recording typically take up much less than 1MB of space. The drawback to MIDI music is that it can sound rather artificial and cold. After all, a computer emulating a saxophone is not the same thing as a real saxophone.

You need to understand the difference between these sound formats so that you can choose the correct format when recording sounds for your presentation, or when choosing recorded music. Keep in mind that whenever you use a WAV file in a presentation, you will add considerably to the presentation's file size. But also keep in mind that when you choose MIDI over WAV for your music, you get a different type of music, one that sounds more artificial.

Caution 

The sounds that come with Microsoft Office are royalty-free, which means that you can use them freely in your presentation without paying an extra fee. However, if you download sounds from the Internet or acquire them from other sources, you must be careful not to violate any copyright laws. Sounds recorded from television, radio, or compact discs are protected by copyright law, and you or your company might face serious legal action if you use them in a presentation without the permission of the copyright holder.

To hear the difference, do the following exercise as an experiment:

1. In Windows, use the Search feature to locate the sample MIDI files that came with Windows. To do so, search for *.mid.

   Note 

   Windows Vista does not come with any sample sounds. However, if you have Windows XP, or if you upgraded from Windows XP to Windows Vista, then you will have some sample sounds.

2. Double-click one of the files to play it.

3. Use Search (or Find) to locate some sample WAV files that came with Windows. To do so, search for *.wav.

4. Double-click one of the files to play it.

Can you hear the difference?