of Microprocessors

758 MUSICAL ApPLICATIONS OF MICROPROCESSORS
whistles, etc., are seldom heard anymore. Electronic generators are cheaper,
offer a much wider variety of distinctive sounds, and can be smaller and
louder with less power input than their mechanical counterparts. In
consumer products, the use of sound generators is increasing dramatically.
Cars beep when the key is left in, watches buzz on the hour, alarm clocks play
reveille, and smoke alarms squeal when guests light up. The use of speech
synthesis is also frequently heard in products such as microwave ovens,
elevators, cars, and children's toys.
In video game design, proper selection and use of sound effects is
almost as important as the screen graphics. In a well-designed game, every
type of movement and event has a different sound associated with it. A
trained listener can determine the state of the game and perhaps even keep
score merely by listening. Often, a separate microprocessor is used exclusively
to generate game sounds. Although uninformed charges that video game
sounds are "carefully selected for maximum subliminal effect" are sometimes
made, in reality they are chosen for generation ease. Most shots and
explosions are simply bursts of filtered white noise, while the typical "laser
zap" can be generated with a dozen instructions or so in the mircoprocessor
program. However, more recent arcade game designs use multipart musical
sequences and even speech synthesis to encourage players.
Moving into more musical applications, there are a large number of
low-cost musical instruments on the market ranging from $30 toy keyboards
to complete polyphonic synthesizers for a few hundred dollars. Many of these
emphasize an ability to store keyboard sequences and play them back later,
since this is easily implemented and requires little if any additional hardware.
There are even $10 musical calculators that "play" the answer with a different
pitch for each digit, $3 musical Christmas cards that playa rune when
opened, and musical car horns for use late on Saturday nights. Several games
make use of random note sequences to test the player's ability to remember
them.
Except for the inexpensive synthesizers, most of these devices are
monophonic and use a square or pulse waveform for the sound source. Where
size is important, such as in the Christmas card, piezoelectric transducers are
used. There are flat ceramic disks about 1 inch in diameter that give an
extremely tinny sound due to a high self-resonant frequency and lack of a
baffle. The toy organs and synthesizers usually have a standard dynamic
speaker built in and occasionally an ourput jack for an external audio system.
Another large application area is in home and personal computers.
Virtually every such computer made since the late 1970s has some means of
sound generation built in. Sound is most commonly used in computer
games, many of which are modeled after successful arcade versions. In
business applications, audible feedback from keystrokes and discreet error
beeps can dramatically improve operator accuracy. All computers with sound
capability have music programs available for them. Even the simplest sound