The Echo II was a plug-in expansion card, speech synthesizer card for the Apple II and Apple IIe personal computers that allowed applications to use speech synthesis. The Echo II used the TMS5220 speech synthesis chip to synthesize speech. The Echo II software could synthesize either unlimited text-to-speech using stitched phonemes, or play back raw LPC data for specific words, with resulting higher speech quality.
LPC (linear predictive coding) was the speech synthesis technology used, which allowed applications to encode speech data in a compact form. The Echo II used the TMS 5220 LPC Speech Chip which was popular in other speech synthesizers