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.

Fixed codebook search for celp speech coding

Abstract: A fixed codebook response is able to better characterize an input signal of a vocoder because the entries of the fixed codebook are tailored to the input signal being processed. A uniformly distributed random noise signal is stored in a transmitting vocoder. During encoding by the transmitting vocoder, the noise signal is shaped by a weighing filter and a pitch sharpening filter, which are condition controlled by the linear predictive coding, pitch and pitch gain characteristics of the input signal being encoded. The shaped noise signal is passed though a thresholding filter to arrive at a pulse sequence having a given sparcity. The fixed codebook response is chosen as that portion of the pulse sequence which best matches a residual signal of the input signal. The indexed location of that portion along the pulse sequence is designated as the fixed codebook bits which are included within the bit frame. The identical random noise signal is stored in a receiving vocoder. The linear predictive coding, pitch, and pitch gain characteristics are part of the bit frame, and are again used to produce an identical pulse sequence. The fixed codebook bits of the bit frame are used to index the pulse sequence to the best matching portion, and hence the fixed codebook response for the bit frame.

Flexible and scalable combined innovation codebook for use in celp coder and decoder

Abstract: In a CELP coder, a combined innovation codebook coding device comprises a pre-quantizer of a first, adaptive-codebook excitation residual, and a CELP innovation-codebook search module responsive to a second excitation residual produced from the first, adaptive-codebook excitation residual In a CELP decoder, a combined innovation codebook comprises a de-quantizer of pre-quantized coding parameters into a first excitation contribution, and a CELP innovation-codebook structure responsive to CELP innovation-codebook parameters to produce a second excitation contribution

Pitch-controlled variable bitrate CELP speech coding

Abstract: Most research in efficient speech coding concentrated for many years on algorithms which produced a fixed bit rate. Fixed bit rates are, however, not a requirement for modern packet‐based telecommunications and computer networks as well as voice storage applications. This makes the implementation of speech coders feasible, which adapt to the changing properties of speech for improved efficiency or quality. Variable bit‐rate coding has therefore become the focus of considerable research activity in recent years [A. Gersho and E. Paksoy, ‘‘Variable Bit Rate Coding,’’ Signal Processing VII, Theories and Applications, EUSIPCO 1994, pp. 1169–1173; L. Zhang et al., ‘‘A CELP Variable Rate Speech Codec with Low Average Rate,’’ ICASSP 1997, pp. 735–738; B. C. Xydeas, ‘‘Source Driven Variable Bit Rate Prototype Interpolation Coding,’’ ICASSP 1996, p. 220; B. Shen et al., ‘‘A Robust Variable‐Rate Speech Coder,’’ ICASSP 1995, p. 249]. While all of these coders focus on classification procedures for efficient bit allocation, the analysis frame size remains mainly static. The coder featured in this paper adapts the analysis frame size and bit allocation according to the pitch of the signal. A pitch frame extractor and classifier at the front end feeds the detected frame into the speech coding back end, which uses traditional CELP‐based techniques [B. S. Schroeder et al., ‘‘CodeExcited Linear Prediction (CELP): High Quality Speech at Very Low Bit Rates,’’ ICASSP 1985, pp. 937–940]. This approach allows the reduction of the bit rate from a constant 4800 bps (bits per second) with original CELP to typically 3200–4000 bps, depending on the speech situation. This figure is even reduced to typically 2600–3200 with the inclusion of Voice Activity Detection. The speech quality equals the quality of the original CELP coder.

Complexity reduction for FS-1016 with multistage search

Abstract: CELP speech coders have proved to be efficient for the coding of speech at medium and low bit rates. The NSA has recently introduced the Federal Standard 1016, CELP speech coder at 4800 bps. We propose two algorithms that reduce the complexity of this coder by a factor 2. The first algorithm uses the particular structure of the standardised code book to simplify the calculation of the cross-correlation term. The second algorithm is a multistage method by subsampling that eliminates nonrelevant code book sequences for the calculation of the energy term. >

Methods for audio signal encoding and decoding

Abstract: Disclosed are an apparatus and a method for encoding/decoding for high-frequency bandwidth extension. The coding method comprises determining a core coding mode of a low-frequency signal of an input signal, based on characteristics of the low-frequency signal of the input signal, quantizing a linear prediction coefficient (LPC) from the low-frequency signal of the input signal. The method includes performing code excited linear prediction (CELP) coding on an LPC excitation signal of the low-frequency signal of the input signal when the core coding mode of the low-frequency signal of the input signal is determined to be a CELP coding mode. The method includes performing time-domain (TD) extension coding on a high-frequency signal of the input signal when the CELP coding is performed on the LPC excitation signal. The method includes performing audio coding on the LPC excitation signal when the core coding mode of the low-frequency signal of the input signal is determined to be an audio coding mode. The method includes performing frequency-domain (FD) extension coding on the high-frequency signal of the input signal when the audio coding is performed on the LPC excitation signal.