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.

Layered celp system and method

Abstract: Layered code-excited linear prediction speech encoders/decoders with progressively weakening perceptual weighting filters for the enhancement layers in the encoder and progressively weakening short-term postfilters for increased bit rates (enhancement layers) and a long-term postfilter for all bit rates.

M-LCELP speech coding at 4 kbps

Abstract: This paper presents the M-LCELP (multi-mode learned code excited LPC) speech coder, which has been developed for the North American half-rate digital cellular systems. M-LCELP develops the following techniques to achieve high-quality synthetic speech at 4 kbps: (1) Multimode and multi-codebook coding, (2) Pitch lag differential coding with pitch tracking, (3) A two-stage joint design regular-pulse codebook with common phase structure in voiced frames, (4) An efficient vector quantization for LSP parameters, (5) An adaptive MA type comb filter to suppress excitation signal inter-harmonic noise. The MOS subjective test shows that 4.075 kbps M-LCELP synthetic speech quality is high, and that its quality is mostly equivalent to that for an 8 kbps North American full-rate VSELP coder. >

Fine granularity scalability speech coding for multi-pulses celp-based algorithm

Abstract: A method for speech processing in a code excitation linear prediction (CELP) based speech system having a plurality of modes including at least a first mode and a consecutive second mode. The method includes providing an input speech signal, dividing the speech signal into a plurality of frames, dividing at least one of the plurality of frames into sub-frames including a plurality of pulses, selecting a first number of pulses for the first mode, with a second number of remaining pulses in the frame plus the first number of pulses in the first mode for the second mode, providing a plurality of sub-modes between the first mode and the second mode, forming a base layer, forming an enhancement layer, generating a bit stream including a basic bit stream and an enhancement bit stream, wherein the basic bit stream is used to update memory states of the speech system.

Variable bit-rate CELP coding of speech with phonetic classification

Abstract: A variable bit-rate speech coder intended for digital cellular applications is described. A voice activity detection algorithm is used to distinguish active speech from background noise. Each frame of active speech is further classified to distinguish between three phonetic categories: voiced, unvoiced, and onset. Each input frame is assigned one of five bit rates according to voice activity and phonetic classification and coded using an analysis-by-synthesis algorithm tailored to the needs of the class that it belongs to. The resulting coder, called Variable Rate Phonetic Segmentation, produces good quality speech at an average bit-rate below 3 kbit/s when operating with a voice activity factor of 0.5. Informal subjective quality assessment for speech in clean and noisy backgrounds indicates a performance that is comparable to the TIA standard QCELP algorithm while operating at a 25% to 40% lower average bit rate.

Low-complexity speech coding with backward and inverse filtered target matching and a tree structured mutitap adaptive codebook search

Abstract: A family of low-complexity, high quality CELP speech coders are described which use two new techniques: Backward and Inverse Filtered Target (BIFT) for fixed codebook excitation search; and Tree-Structured Multitap adaptive codebook search. Incorporation of these new techniques resulted in very low complexity CELP coders at less than 16 Kb/s. The three coefficients for linear combination of the adaptive codebook are chosen from a tree-structured tap codebook. The best tap index in the primary codebook points to a secondary codebook where the search is further conducted. This procedure may be repeated many times, wherein each subsequent tap codebook points to yet another subsequent tap codebook, which points to yet another subsequent tap codebook, etc. A fixed ternary excitation codebook using a new technique called Backward and Inverse Filtered Target matching (BIFT), is used to encode the portion of the target signal that is left behind after the adaptive codebook contribution has been subtracted. BIFT combines the elements of the Backward Filtered Target response and Inverse Filtered Target response by element-by-element multiplication to define a new vector. A predetermined number of maximums of the new vector are chosen as the pulse locations and the signs assigned are the same as the signs of the corresponding elements.