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Video: Quality Sound
In recent years, video technology has created new opportunities in educational media. This increase in video technology has put greater demands on school sound systems and technicians to provide better sound for video. These simple tips will help you deal with many of the problems that may arise when working with the marriage of audio and video. The oldest form of moving pictures used in schools today is the 16 mm film projector. You're probably very familiar with the "built-in" speakers in these ancient workhorses. The sound was usually distorted with very little high frequency response or intelligibility. The projector also was too loud for those sitting nearby, yet it couldn't be heard clearly by those sitting further away. A device called a direct box will solve this dilemma. Figure 1  Direct Box Improves Audio The direct box is designed to accept an audio signal from a cassette deck, mixer, keyboard, string instrument, or power amplifier (including the "extension speaker" output from a film projector). This box changes the level and impedance of this signal to match a normal microphone output. With a regular microphone cable, you can take the output of the direct box and plug into a nearby microphone jack (Figure 1). Now, the sound track from the film can be heard through the main sound system or even through a portable sound system. In open-format classrooms the sound can be evenly distributed through ceiling speakers. This will keep the overall level down so as not to disturb nearby classes. The direct box got its name from the music industry because it allowed guitar and bass players to plug directly into a sound mixer without an amplifier. Many types and styles of direct boxes that vary in cost and flexibility are available. Make certain that the type of direct box you select has several types of input connectors, including RCA and 1/4" phone jacks, so that you can use it with cassette decks, VCR's, film projectors, etc. The current trend in school video is the video cassette recorder which uses 1/2" VHS tapes. For the purposes of this article, we will assume that for most situations, schools will not use the 3/4" U-matic or l" VTR formats. However, the principles are the same. For most of us, VCR's and camcorders have become fairly standard pieces of equipment. The sound track on a VHS tape played on a VCR can also be handled with a direct box as mentioned above. Look for the audio output(s) or auxiliary output. Make certain that you are plugging into an audio output and not a video output. (You probably won't hurt anything if you make a mistake, but you will hear strange and curious sounds coming from the sound system.) These audio outputs will normally be RCA phono jacks. If your VHS tape has a stereo sound track and your VCR has stereo audio outputs, you may need two direct boxes. It's usually better to use just one channel, but if both channels are important, then use two direct boxes. It is not recommended to use a Y cable to mix the stereo outputs of the VCR. In fact, that advice applies to any electronic equipment. Better Video Sound The other area of sound for video is in the video recording process. Camcorders (short for camera recorder) are becoming an integral part of many school events including sports activities, theatrical productions, awards and graduation ceremonies and guest lecture series. Although most camcorders have an attached microphone, I doubt very much if anyone has ever really been happy with the quality of sound that gets recorded. This attached microphone has a habit of picking up more noise from the audience than from the program itself. And even if the audience noise was not a problem, the camcorder is so far away that the reverberation in the room causes the program audio to be very hollow or indistinct. Figure 2  So what's the answer? One is to place a microphone closer to the source of sound (Figure 2). This will help reduce the reverberation effects and crowd noise. However, a cable will have to be run back to your camera position making you locked to one position. Also, since there is only one microphone, you will not have much control on the audio balance or mix. Careful planning and positioning of the microphone will certainly help improve the audio. The best way to improve the audio is to feed the signal from the sound system mixer into the microphone input jack on the camcorder. There are two ways to do this. If your school has a hearing- impaired system, attach one of the personal pocket receivers to the camcorder. Then, plug a cable from the earphone output jack on the pocket receiver into the microphone input on the camcorder. Be sure to test and adjust the receiver's volume control to prevent distortion on your tape. You may need an attenuated cable to decrease the volume to the camcorder. Also, make certain that there's a fresh battery in the receiver. This approach will allow the camcorder operator to go anywhere in the room without worrying about distractions such as floor cables. Figure 3
 The second way to get sound from your mixer to the camcorder is to use either an existing microphone line or an external cable (Figure 3). The best way to do this is to use a direct box at the mixer. The output of the mixer is plugged into the direct box. The microphone level output from the direct box is then plugged into a microphone line or external cable. At the other end, you will need an adaptor cable that has a female 3-pin mic connector at one end and a mini phone jack on the other (connectors and adaptors will vary somewhat depending on your specific equipment). Sound Planning Professional-sounding audio for your video tape requires some effort and planning. Each solo or group of instruments will probably need a microphone. If you want to hear some audience reaction, you will have to be able to add an audience microphone into the mix that is going to the video tape. This record mix should be separate from the main mix because you cannot add audience sound into the main sound system without a feedback howl. You also may not need to amplify some acoustic instruments. For example, in a musical production the orchestra is probably not being amplified by the sound system, but you will need a microphone turned on if you want the orchestra to be heard on the tape. Your mixer will need a separate output mix in order to get a properly balanced recording. Some schools even use a totally separate mixer for their video and audio tape recording. Please feel free to call us if you need help in getting better sound for your video tapes. We'll be glad to recommend specific microphones and to answer your questions. We'd also like to supply your direct box needs. Just give us a call. by Travis Ludwig © 1996 Internet Sound Institute (www.soundinstitute.com). This article is for personal use only. Any commercial reproduction is not permitted without permission. To obtain permission, contact ISI at hopi@soundinstitute.com
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