PROJECT 5 : Melody Camouflage

Erroneously perceived sound while masked by noise

Suggested Entry Category

• Behavioral & Social

Purpose or Problem

The purpose is to prove that often people “hear” what they expect to hear, even if the sound is not present.

Overview

Have you ever listened to a blank cassette tape on a stereo that had the volume set loud? All you hear is a high-pitched hissing sound. This “noise” is due to the nature of tape as a recording medium.

“Noise” in the reproduction of audio is unwanted sound caused by the tape and electronic components in the  amplifier. This hissing sound was not part of the original source material. Tape hiss has plagued the music and audio industry for years. Today, electronics has advanced to the point that hiss caused by electronic circuitry is almost nonexistent, especially on professional audio equipment. Another technological breakthrough, the compact disc (CD), has made a tremendous advancement in reducing audible hiss in recorded music.

A psychoacoustical masking effect takes place when music is played at high volumes. Noise such as tape hiss seems to disappear during loud passages of music. Another interesting behavioral effect is that we sometimes hear what we expect to hear. In this project, we record music and “white noise” together, and then gradually reduce the music until only the white noise remains. Will people claim to continue to “hear” the music in the presence of white noise, even after it is turned off? 

Hypothesis
Hypothesize that, when tested, a greater number of your friends and classmates will continue to “hear” music even after the music has completely stopped, while the presence of a high level of white noise remains.

Materials’ List
• Stereo audio mixer
• Blank cassette tape
• Headphones
• Cassette player
• Cassette recorder
• Cassette tap of a popular song all your test subjects are very familiar with
• Electronic music synthesizer keyboard with a white noise sound
• 20 friends and classmates
• Stop watch or a clock/watch with a seconds display

Procedure
The volume level of the white noise will be held constant. The volume level of the music will be varied. You need to make a cassette tape with which to test your subjects. The tape must contain white noise recorded at a high volume, along with a song your test subjects are very familiar with.

To do this, you need a source of white noise, such as a musical instrument synthesizer keyboard, which has a white noise–like setting. Connect the synthesizer’s output into an audio mixer. Into another channel of the mixer, connect the output of a cassette tape player. The output of the mixer must then feed another cassette recorder that has a blank tape to record the results.

If you do not have access to an audio mixer, you can use a musical instrument amplifier, such as a guitar amplifier, as long as it has two separate input channels, each with its own volume control. Place two microphones (for left and right channels) by the amplifier’s speaker, and plug them into a cassette recorder to record the results on a blank tape.

You will make a one-minute recording. Cue the blank tape past the cassette’s leader (the plastic part of the tape at the beginning of the cassette). Set the volume of the white noise source fairly high. Set the volume of
the music being played at about an equal volume. Start the recorder, the white noise generator, the music tape, and a stop watch. After ten seconds, slowly begin to turn the volume of the music tape down, but leave the white noise at a constant level. The music fade must be very, very slow. Pace yourself so that at 50 seconds into the song, the volume will be 100 percent reduced. At 60 seconds, stop the tape recorder.

Once you make your test tape, place it in a cassette player with headphones. Have a friend wear the headphones and tell him or her to push the play button. Be sure you have cued the tape up past the leader at the beginning of the tape, so when the play button is pressed, your test recording begins to play. Start timing the instant the tape begins to play. Ask your friend to tell you as soon as he or she hears the music stop playing. 

Remember, at 50 seconds into the tape, the music is gone. Does the tape recording end (at 60 seconds) before your friend says the music has stopped? Does your friend say the music never stopped? Test at least 20 friends, and write down whether each one could correctly identify that the music ended before the tape recording ended.

Results

Write down the results of your experiment.

Conclusion

Come to a conclusion as to whether or not your hypothesis was correct.

Something More

1. Does age have any effect on your results? In other words, do more young people continue to “hear” the
music when it is gone than do people over age 50?
2. Does gender have any effect on your results?
3. People may claim to continue to hear what they expect to hear, but what if the music played to them was a song they were not familiar with? Would they still claim they were hearing music when it was no longer playing?