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Understanding Sound Files
Computer sound files come in many different formats, but there are two broad categories: wave and MIDI.The term wave 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 wave file in a generic sense of the word because it was originally a "sound wave" in the air that the microphone captured. The tracks on an audio CD can also be considered wave files because at some point, presumably, a person went into a recording studio and made music with voice or instruments that was recorded. Similarly, the very popular MP3 music format is a wave format. Other wave formats include .rmi, .au, .aif, .wma, and .aifc. Wave files are very realistic sounding because they are basically recordings of real-life sounds. The drawback to wave files is that the file size is typically large. It's important to remember that "wave" in a generic sense is different from WAV the file format. Many of the Windows and Office sound effects are in WAV format, and WAV format is the only sound format that can be embedded in a PowerPoint presentation. WAV is far from the only wave type of sound, however.The other category is Multi-Instrument Digital Interface (MIDI), which refers to the interface between a computer and a digital instrument such as an electric keyboard. When you make a MIDI recording, there is no analog source-it is purely digital. For example, you press a key on a keyboard, and that key press is translated into an instruction and written in a computer file. There is no microphone and no sound waves in the air. The sound it makes is completely up to the software.MIDI files usually have a .mid extension. They are smaller in size than wave files. Several minutes of recording typically takes up much less than 1MB of space. The drawback to MIDI music is that it can sound rather artificial and computer-like. A computer emulating a saxophone is not the same thing as a real saxophone, after all.It's important to understand the difference between wave and MIDI so you can choose the right format when recording sounds for your presentation or when choosing recorded music. Keep in mind that whenever you use a wave file in a presentation, you may be adding considerable bulk to the presentation's file size (unless you link to an external wave file, in which case you would have to make sure the file continued to be available). Also, keep in mind that when you choose MIDI, you get a different type of music, one that is more artificial-sounding.| Caution | The sounds that come with Microsoft Office are royalty-free, so you can use them freely in your presentation without paying an extra fee. If you download sounds from the Internet or acquire them from other sources, however, you must be careful not to violate any copyright laws. Sounds recorded from television, radio, and audio CDs 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. |
