Abstract
The Enhanced Variable Rate Coder (EVRC), standardized by the Telecommunications Industry Association (TIA) as IS-127, is intended for use with the IS-95x Rate Set 1 air interface (CDMA). This coder operates at a maximum rate of 8.5 kb/s and an average rate of about 4.1 kb/s on conversational speech. The EVRC consists of three coding modes that are all based on the Code Excited Linear Prediction (CELP) model. Selection among the three modes is based on an estimate of the input signal state, with active speech encoded primarily at 170 bits/20 msec frame (Rate 1), background noise and silence encoded at 16 bits/frame (Rate 1/8), and some active speech and essentially all transitions between speech and silence encoded at 80 bits/frame (Rate 1/2). In order to improve performance in the presence of background noise, the EVRC employs an adaptive noise-suppression filter at the input. Subjective test results are presented demonstrating that the EVRC delivers excellent quality voice in clean speech/clear channel conditions, and that its performance exceeds that of most currently standardized speech coders for wireless applications in background noise and/or impaired channel conditions.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
Explore related subjects
Discover the latest articles, news and stories from top researchers in related subjects.References
Atal, B.S. and Schroeder, M.R. (1984). Stochastic coding of speech at very low bit rates.Proc. Int. Conf. Comm., Amsterdam, pp. 1610–1613.
Chen, J.-H. and Gersho, A. (1995). Adaptive postfiltering for quality enhancement of coded speech.IEEE Trans. on Speech and Audio Processing, pp. 59–71.
Gardner, W., Jacobs, P., and Lee, C. (1993). QCELP: A variable rate speech coder for cellular networks. In B.S. Atal et al. (Eds.),Speech and Audio Coding for Wireless and Network Applications, pp. 85–92.
Hagen, R. et al. (1998). Removal of sparse-excitation artifacts in CELP.Proc. ICASSP, pp. 145–148.
Itakura, F. (1975). Line Spectrum representation of Linear Predictive Coefficients of Speech Signals,J. Acous. Soc. Am., 57:535(A).
Kjeijn, W.B., Kroon, P., and Nahumi, D. (1994a). The RCELP speech-coding algorithm.European Transactions on Telecommunications, 5(5):573–582.
Kleijn, W.B., Ramachandran, R.P., and Kroon, P. (1994b). Interpolation of the pitch-predictor parameters in analysis-by-synthesis speech coders.IEEE Trans. on Speech and Audio Processing, pp. 42–54.
Kleijn, W.B. et al. (1985). Improved speech quality and efficient vector quantization in SELP,Proc. ICASSP, pp. 155–158.
Laflamme, C, Adoul, J.-P., Salami, R., Morissette, S., and Mabilleau, P. (1991). 16 kbps wideband speech coding technique based on algebraic CELP,Proc. ICASSP, pp. 13–16.
Leigh Thorpe—Subjective evalation of speech coders (this issue).
Nahumi, D. and Kleijn, W.B. (1995). An improved 8 kb/s RCELP coder.Proc. IEEE Speech Coding Workshop, pp. 39–40.
Oppenheim, A.V. and Schafer, R.W. (1975).Digital Signal Processing, New Jersey: Prentice-Hall Inc., pp. 113–114.
Salami, R., Laflamme, C., Adoul, J.-P. et al. (1994). A toll quality 8 kbps speech coder for personal communication systems (PCS).IEEE Trans. on Vehicular Technology, pp. 808–816.
TIA/EIA (1993). Mobile station-base station compatibility standard for dual-mode wideband spread spectrum cellular system, IS-95.
TIA/EIA, TR45 (1996). Enhanced variable rate codec, speech service option 3 for wideband spread spectrum systems. Interim Standard IS-127.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Recchione, M.C. The Enhanced Variable Rate Coder: Toll quality speech for CDMA. Int J Speech Technol 2, 305–315 (1999). https://doi.org/10.1007/BF02108646
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF02108646