Sound and Melody Chips Explained
Everyone has heard these devices in action they are ubiquitous: in children's' toys, consumer and promotional items. If it talks, sings, plays music, flashes lights, or is motor-actuated (or any combination thereof) it is likely that one of these sound chips is controlling things.
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Sound Chips are semiconductor devices that can play recorded sound that has been specially encoded. This is a mass-produced "masked ROM" IC (integrated circuit) not a recordable chip. The process is akin to comparing mass-produced CDs and "burned" CD-Rs. The mass-produced product's unit cost much, much less. Sound chips are also logic devices with power ranging from a simple logic device to a full-blown micro-controller. These products have a wide variety of I/O (input/output) options including analog and digital sound out (in single and multi-channel configurations) and plenty of input pins for switches, keypads and real world sensors. There are also plenty of output pins to trigger motors, lights and LEDs (including some built-in LED controlling features). With creative programming, sound chips can product an engaging simple effect or full blown animation and interactivity.
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Melody Chips are semiconductor devices that contain built-in music synthesizers (in a variety of channel output configurations). Melody chips are also logic devices with simple to sophisticated features (as stated above). However, there is no audio playback capability. Instead the internal synthesizers playback according to software instruction. In musician terms a melody chip is a "sequencer." Because melody chips have a much smaller memory requirement (not having to store recorded sound) they are "dirt cheap" to produce. Originally melody chips were used to produce the sound in "musical greeting cards." But they've come along way from those incredibly annoying, gritty, nasally tones. Wavetables can be imbedded into some of today's melody chips so they can play customer-supplied sounds instead. The low price and sophistication of these products is compelling for many uses.
Sound and Melody Chips are a combination of the two kinds described above. These devices have the capability of playing a music bed (in the melody/wavetable synthesizer) while the "speech" section plays recorded sounds "on top" and a LED array is performing a "marquee" pattern.
Terms. The terms "speech" and "melody" come from the early days of the semi-conductor boom in consumer items, particularly toys.
"Melody," "Dual-Tone Melody" and "Quad Tone Melody" (dual and quad referring to the number of independent "parts" the device could play simultaneously. These were the first "consumer sound chips" and were used in "musical greetings cards" first in the late 70s and early 80s (and still used today).
"Sound" referred to a new chip that could play back real world sounds instead of the synthesizers (which could only play "melodies"). Because the main use was in talking toys sound chips ended up being called "speech" chips even if they were used for sound effects or music playback.