Wikipedia
The Mockingboard is a sound card for the Apple II family of microcomputers built by Sweet Micro Systems. The standard Apple II machines never had particularly good sound, especially when compared to competitors like the SID chip-featuring Commodore 64. With the notable exception of the Apple IIGS, all an Apple II programmer could do was to form sounds out of single clicks sent to the speaker at specific moments, which made the creation of complex sounds extremely difficult to program and made it mostly impossible to do any other processing during the creation of sounds. Early (1978) hardware accessories such as ALF's Apple Music Synthesizer focused on producing only music. In 1981, Sweet Micro Systems began designing products not only for creating music, but speech and general sound effects as well. Its specialized hardware allowed programmers to create complex, high-quality sound without need for constant CPU attention. The Mockingboard could be connected to the Apple's built-in speaker or to external speakers. However, as the quality of the built-in speaker was not high, the instruction manual recommended obtaining external speakers.
The Mockingboard was available in various models for either the slot-based Apple II / Apple II Plus / Apple IIe systems or in one special model for the Apple IIc. Sound was generated through one or more AY-3-8910 or compatible sound chips, with one chip offering three square-wave synthesis channels. The boards could also be equipped with an optional speech chip (a Votrax SC-01 or compatible).
Some software products supported more than one Mockingboard. Ultima V supported two boards, for a total of 12 voices, of which it used eight. Most other programs supported at most one board with six voices.
Applied Engineering's Phasor was compatible with the Mockingboard. It had 4 sound chips and thus provided 12 audio channels. Few programs supported using it for more than six voices, however.
In 2005, an Apple II retrocomputing hardware company, ReactiveMicro.com, cloned the Mockingboard and offered it for sale. It is also fairly easy to build a clone on a prototyping board, since the Mockingboard contains relatively few components.
An IBM PC-compatible version was developed, but was only distributed with Bank Street Music Writer.