19.020 What is "old Apple" sound and how is it produced?
Description
This article is from the Apple II Csa2 FAQ, by Jeff Hurlburt with numerous contributions by others.
19.020 What is "old Apple" sound and how is it produced?
All Apple II computers can produce "Old Apple" sound without any special
boards or add-ons. The system BEEP you hear upon a Reset is an example.
The sound is produced by code which addresses memory location $C030. Each
time $C030 is referenced the output of a flip-flop going to a simple audio
amplfier stage changes state.
For example, in BASIC, X= PEEK(49200) will produce a single click. In
machine code, so would AD 30 C0 (Load Accum from address $C030). Duration and
Frequency of sound can be set by placing the address reference instruction
inside a loop and using other loops to control speed of references.
Although the signal going to the internal amplifier is always a square
wave, creative coding by music enthusiasts, game developers, and other users
has produced remarkable effects ranging from two-voiced music and game sounds
to speech.
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By: Mitch Spector
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