Enhanced Variable Rate CODEC (EVRC) is a speech codec used in CDMA networks. It was developed in 1995 to replace the QCELP vocoder which used more bandwidth on the carrier's network, thus EVRC's primary goal was to offer the mobile carriers more capacity on their networks while not increasing the amount of bandwidth or wireless spectrum needed. EVRC uses RCELP technology, which Qualcomm claims improves speech quality with lower bit rates.
EVRC compresses each 20 milliseconds of 8000 Hz, 16-bit sampled speech input into output frames of one of three different sizes: full rate – 171 bits (8.55 kbit/s), half rate – 80 bits (4.0 kbit/s), eighth rate – 16 bits (0.8 kbit/s). A quarter rate was not included in the original EVRC specification and eventually became part of EVRC-B.
A zero length frame is included in the specification for 'null' and erasure frames. The eighth (1/8) rate is not intended for speech signals, but instead for background noise. Due to the source controlled nature of the codec the average bit rate varies based on network conditions, but is usually around 6 kbit/s.
EVRC was replaced by SMV which retained the speech quality and at the same time improved network capacity.
Recently, however, SMV itself has been replaced by the new CDMA2000 4GV codecs. 4GV is the next generation 3GPP2 standards-based EVRC-B codec. 4GV is designed to allow service providers to dynamically prioritize voice capacity on their network as required.
EVRC can be also used in 3GPP2 container file format - 3G2.
Famous quotes containing the words enhanced, variable and/or rate:
“Art is beauty, and every exposition of art, whether it be music, painting, or the drama, should be subservient to that one great end. As long as nature is a means to the attainment of beauty, so-called realism is necessary and permissable [sic], but it must be realism enhanced by idealism and uplifted by the spirit of an inner life or purpose.”
—Julia Marlowe (1866–1950)
“There is not so variable a thing in nature as a lady’s head-dress.”
—Joseph Addison (1672–1719)
“Strange that the vanity which accompanies beauty—excusable, perhaps, when there is such great beauty, or at any rate understandable—should persist after the beauty was gone.”
—Mary A. [Elizabeth, Countess Von] Arnim (1866–1941)