ATARI HOME HEARING TEST
Play it again, computer!by CHARLES JACKSON
Your Atari can test you for pitch hearing, just about like those grade school tests. This short BASIC program works on all Atari computers of any memory size, with disk or cassette.
Remember when you were in second grade and they sent you down to the school nurse's office for a hearing test? The nurse seated you at a desk, shoved big gray headphones over your ears and fiddled with console knobs like a mad scientist
Relive those golden days of elementary school by taking your own Atari Home Hearing Test. Or inflict the experience on somebody else.
Type in Listing 1, HEAR.BAS, check it with TYPO II and SAVE a copy before you RUN it.
This test measures high frequency hearing responses just about the same way as your old school test. It starts by playing a pitch so high only your dog can hear it. Then gradually the pitch is lowered. Signal with your joystick when you can hear the pitch. This will stop the descending tone. (Make sure your video volume is turned up loud enough so you can hear the test tone.)
The human voice sings within the range of about 50 Hz to 1 kHz. (Hz stands for hertz, a unit of measure equal to one cycle per second.) A bird whistles above 3 kHz. A truck rumbles below 10 Hz.
People can hear from about 20 Hz to 20 kHz, depending on their age and the sound loudness. Children can usually hear higher pitched sounds than adults. If you've been to too many heavy metal concerts lately, you may have experienced some high frequency hearing loss.
HOW IT WORKS
The Atari has three internal clock frequencies, 15 kHz, 64kHz, and 1.79 MHz. Humans can't hear the 1.79 MHz or 64 kHz clocks directly, but all of the clocks can be used with the SOUND command.
The built-in sound generators can be accessed in BASIC with the command SOUND A,B,C,D, where B is the pitch, or frequency value. But sometimes using the SOUND command resets some of the parameters, like the clock. So it is useful to change frequencies without using the SOUND command.
This program changes the pitch by POKEing 53760, which controls the frequency for voice 0.
The frequency is found by dividing the clock frequency by twice the value placed in parameter B of the SOUND command. This is calculated in line 50 of the program. For example,
plays the pitch A = 220 Hz, when the clock is set to 64kHz. (64 kHz
= 64,000Hz, 64,000Hz/ 2/ l45 = 220 Hz.)
Clock frequencies can be changed by poking address 53768 (dec) with:
0 for 15 kHz clock
1 for 64 kHz clock
32 for 1.79 MHz on channel 2
64 for 1.79 MHz on channel 0
96 for 1.79 MHz on channels 0 and 2.
Charles Jackson of Santa Monica, California is not Antic Program Editor Charlie Jackson.