Code-excited linear prediction

About: Code-excited linear prediction is a research topic. Over the lifetime, 2025 publications have been published within this topic receiving 28633 citations. The topic is also known as: CELP.

Enhancement of reverberant speech using the CELP postfilter

Abstract: In this paper we investigate the application of adaptive postfiltering for the enhancement of reverberant speech. The considered method is commonly used in Code Excited Linear Prediction (CELP) speech coding to lower the impact of quantization noise in the excitation signal and the spectral envelope. We show that the underlying additive noise model is accurate enough to enhance speech which is recorded in an enclosed space where the resulting early reflections are usually modeled as a convolutive distortion. By means of adaptive filtering, the amplitudes of the unwanted peaks in the excitation signal are attenuated and the signal components at the harmonic peaks are emphasized. Both, single- and multi-channel dereverberation algorithms are proposed having a moderate computational complexity. Experiments have shown that this approach is capable of reducing early reverberation and attenuate the “distance-effect” arising from room reflections.

Optimizations of ITU G.729 speech codec

Abstract: Modern mobile communications require optimum bandwidth utilization with minimum loss, delay and good quality of speech transmission This triggered the usage of low bit rate voice codecs, among which CELP codecs inherit the merits of both waveform and source codecs, like toll quality, low bit rate etc In this paper several hardware and software optimization techniques are presented for efficient implementation of ITU G729 standard (CS-ACELP, conjugate structure algebraic code excited linear prediction) of 8 Kbit/s bit rate on a real time digital signal processor (DSP), with the aim of overcoming the limitation of computational burden and also scaling this application for enhanced speed to process more channels These techniques are in general applicable to any speech codec and DSP processor platform

Speech compression using CELP speech coding technique in GSM AMR

Abstract: In cellular communication technology, quality of voice output at destination depends on the channel condition. Bad channel condition will produce many errors in the voice output and hence the voice quality. To maintain the voice quality in various channel condition AMR is used. Various modes of bit rate is used in AMR, from low to high bit rate is used depend on the channel condition. Low bit rate modes is used in a bad channel condition to allow more bits for channel coding, while high bit rate on the contrary. Recently various speech (source) coding techniques, such as: CELP, ACELP, RPE-LTP, are used in different applications. In this study the application of CELP in AMR is observed. MATLAB program simulation is used to observe and calculate errors occur in the system. The difference of resulted error produced in AMR using CELP is not significant. From low bit rate (5.9 kbps) to high bit rate (12.2 kbps), the error difference is less than 1%.

Efficient Residual DPCM Using an $l_1$ Robust Linear Prediction in Screen Content Video Coding

Abstract: In this paper, a residual differential pulse code modulation (RDPCM) coding technique using a weighted linear combination of neighboring residual samples is proposed to provide coding efficiency in the screen content video coding. The RDPCM performs the sample-based prediction of residue to reduce spatial redundancies. The proposed method uses the $l_1$ optimization in the weight derivation by considering the statistical characteristics of graphical components in videos in an intracoding. Specifically we use the least absolute shrinkage and selection operator to derive the weights because the solution is accurate in high variance residue. Furthermore, we enhance parallelism in a line processing by restricting the support to the row-wise prediction to above samples or the column-wise prediction to the left samples. The proposed method uses an explicit RDPCM scheme, so a coding mode determined by rate-distortion optimization is transmitted to a decoder. For coding the overhead, we develop a context design in CABAC based on correlation between an intraprediction direction and an RDPCM prediction mode. It is demonstrated with the experimental results that the proposed method provides a significant coding gain over the state-of-the-art reference codec for screen content video coding.

Convergence and Numerical Sensitivity of Backward-Adaptive LPC Predictor

Abstract: Backward-adaptive LPC prediction is a useful and relatively new scheme for low-delay speech coders. However, if not performed carefully, it can lead to numerical sensitivity problems, decoder divergence, or other unexpected problem in this paper, we report four useful techniques: white noise correction, bandwidth expansion, window tuning, and spectral smoothing, which collectively are sufficient to avoid all such problems known to us. All except window tuning are also useful for reducing the numerical sensitivity of forward-adaptive LPC prediction that is commonly used in predictive coders such as CELP, MPLPC, and APC.