Capturing and Storing Sounds for Multimedia Projects
The process of capturing sound bears many similarities to the process of capturing video. In fact, one convenient way to generate an audio file is to use the video editing software we described at an earlier point to separate the video and audio tracks recorded by a digital camcorder, discard the video track, and save the audio. This ends up being a practical solution for capturing sound from remote locations because educators are likely to have access to a camcorder and because the method is simpler than techniques for bringing audio from a portable device such as a cassette recorder into the computer.
Another option is to use programs such as PowerPoint and KidPix, which have built-in capabilities for capturing sound. If the computer contains the appropriate hardware capabilities, one need only plug in a simple microphone (most laptop computers have built-in microphones), click the record button within the software program, and then speak, sing, play a musical instrument, or in some other way generate an audio signal for the program to capture. In this case, the actual process is very similar to the process of capturing video from an analog signal. The microphone brings an analog signal into the computer and specialized hardware then converts the analog signal into digitized sound. Several variables come into play in converting analog sound to digital sound. The first concerns the accuracy with which the analog signal is converted to a digital signal. Analog sound is represented as a continuous sound wave. The conversion to a digital form is accomplished by representing this continuous wave in discrete steps. The more steps there are, the more accurately the original information can be represented. A digital representation allowing 16-bit sound divides the sound wave into 65,536 steps. Hardware allowing 8-bit sound allows only 256 steps in the sound wave to be differentiated and thus produces a lower level of accuracy.
Another variable associated with sound digitizing is the sampling frequency, which is the number of times per second that a digital representation of the analog signal is produced. Sampling frequency is usually described in thousands of samples per second, or kilohertz (kHz). Both the bit depth (8-bit versus 16-bit) and the sampling frequency influence quality and storage requirements. The CD-recorded music that you listen to is probably stored at a bit depth of 16 and a sampling frequency of 44.1 kHz. The sound recorded in the applications described in this chapter would more likely be recorded at a bit depth of 8 and a sampling frequency of 11 kHz. The difference in sound quality is noticeable but acceptable for most purposes. One advantage of the lower-quality sound is that it requires less storage space. A ten-second sound recorded at the lower-quality settings would require only about 115 kilobytes of disk space. The connection between sampling frequency and file size is an issue you may also encounter when saving audio tracks in video applications. For example, iMovie allows the user to select sampling frequencies from 8 to 48 kHz and mono or stereo tracks when saving a movie. Saving audio at a lower frequency and in mono would reduce file size and might be important in creating a reasonable product for web presentation.
Sounds can be stored as independent files or as resources (a component that is part of a mixed file format). When you create a multimedia program with Kid Pix, any sounds that are included are usually incorporated as resources within the stack or the multimedia file. Applications also store sounds as independent files; that is, the file contains nothing but the data necessary to reproduce a sound. Like graphics, sounds can be stored in several different formats. The audio interchange file format (AIFF) is used by many software applications that produce files to be loaded by other programs and other hardware platforms. Windows sound applications frequently use the Waveform Audio (WAV) format. There are even generic formats intended to be shared online. For example, the AU (mm-law) format is commonly used as a component of web pages because it can be interpreted by web software running on several different hardware platforms. In addition, teachers should be aware of the MP3 format. MP3 is an audio layer of the more general MPEG-1 and originally used for music.
It is easy to become so enamored of sounds that you clutter a presentation with a lot of useless noise. The skillful use of sound is another of those design-related matters for which there are probably no hard-and-fast rules. Our approach is a little different. Although student projects should be tasteful, our priority is the kinds of experiences that motivate students and help them work with information actively. Putting together a thirty-second speech about a butterfly or a fish can be a useful experience for a second grader. Agreeing to record a short poem that an elementary-school student writes to accompany a drawing can increase her motivation to write the poem. As a teacher, you will need to consider specific situations and determine when working with sound would meet the criteria of increased motivation or more active involvement with information.