Wednesday, May 16, 2007

Picture But No Sound?

This happens occasionally in our Prairie Lakes AEA Lending Library. A school will return a videotape with a Post-In note attached, saying that when they played the videotape, there was a picture but no sound. Most of the time, the sound is there but the school VCR could not find it.

If this happens, here is the “short answer.”

1. Look at the remote for your VCR. Is there a button marked AUDIO (or perhaps SOUND)? If so, press the button.

2. If you don’t have an AUDIO or SOUND button, then you’ll have to access the MENU for your VCR. What you want to do is change the AUDIO output from HI-FI to NORMAL.

Every menu looks a little different, so I can’t post detailed instructions for your specific equipment.

All right, if you would like to know the theory behind what we just did, here is the “long answer.”

On every VHS tape, the following information is recorded:

A: This is the NORMAL (or LINEAR) audio track. Every VCR, even the oldest RCA SelectaVision VCR from 1977 records audio here.

B: This is the VIDEO TRACK. As you can see, the video is recorded as stripes on an angle.

C: This is the CONTROL TRACK. The control track records 30 electronic pulses per second that are used to synchronize the tracks.

For many VCRs, including very old and very inexpensive ones, this is everything that’s recorded on the tape.

D: Most newer VCRs also are able to record and playback audio in high fidelity sound, or HI-FI. The HI-FI track is embedded in the video track. Our illustration shows the HI-FI track in red.

Sometimes, because of equipment failure or operator error, a Hi-Fi audio track is recorded with no sound. (It’s like there is a highway with no cars on it.) When you play such a tape, your VCR senses there is a Hi-Fi track and plays it. But no sound was recorded on that track…it’s just an empty audio track. So you have picture and no sound.

The solution is to tell your VCR to quit horsing around and just play the NORMAL audio track.

If you are lucky enough to have the remote handy, and if the remote has an AUDIO button, it’s a simple matter to switch from HI-FI to NORMAL audio playback. If that’s not an option, then you have to open the MENU on your VCR and find the AUDIO or SOUND command, and switch that to NORMAL.

Unfortunately, we do sometimes discover a tape with this problem in our library. By selecting the NORMAL audio track playback on your VCR, you will be able to work around this problem and show your video tape in class as planned.