residual-excited linear prediction

Residual-excited linear prediction (RELP) is an obsolete speech coding algorithm. It was originally proposed in the 1970s{{cite journal|last1=Magill|first1=D. T.|last2=Un|first2=C. K.|title=Residual excited linear predictive coder|journal=The Journal of the Acoustical Society of America|date=Apr 1974|volume=55|issue=S1|pages=S81|doi=10.1121/1.1919989|bibcode=1974ASAJ...55...81M|doi-access=free}} and can be seen as an ancestor of code-excited linear prediction (CELP). Unlike CELP however, RELP directly transmits the residual signal. To achieve lower rates, that residual signal is usually down-sampled (e.g. to 1–2 kHz). The algorithm is hardly used anymore in audio transmission.

It is still used in some text-to-speech voices, such as the diphone databases found in the Festival and Flite speech synthesizers.{{cite web |url=http://www.cstr.ed.ac.uk/projects/festival/ |title=The Festival Speech Synthesis System}}{{cite web |url=http://www.cstr.ed.ac.uk/projects/festival/manual/festival_21.html#SEC87 |title=LPC databases (Festival Speech Synthesis System)}}