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.

4 kb/s improved multi-pulse based CELP speech coding with multiple location codebook and post-processing

Abstract: This paper proposes an improved MP-CELP (Multi-Pulse-based CELP) speech coding at 4 kb/s. In MP-CELP, amplitudes or signs of multi-pulse excitation are simultaneonsly vector quantized (VQ). In order to improve speech quality for voiced speech, a multiple pulse location codebook is stored to enhance the coverage of the location. The optimum combination among the pulse location codebook, pulse amplitude codevector and gain codevector is searched for and selected. In order to be robust against background noise, a post-processing efficiently reduces temporal fluctuation for the excitation signal. The subjective evaluation results show that speech quality for 4 kb/s improved MP-CELP is equivalent to that for ITU-T G.726 (32 kb/s) and G.729 (8 kb/s) for both M-IRS and flat clean speech. For background noise conditions, 4 kb/s speech quality is close to that for ITU-T G.726 (32 kb/s).

Combined coding of audio and speech signals using LPC and the discrete wavelet transform

Abstract: The aim of combined coding is to compress a mixed signal consisting of speech and music to the highest possible compression ratio and yet maintain user acceptability. This paper proposes a hybrid coder which is capable of coding combined speech and audio signals sampled over the range 16 kHz to 32 kHz. The coder provides high quality audio coding at competitive bit rates over this range of signal sampling frequencies and offers further coding gains when used with speech signals alone.

Warped linear prediction for improved perceptual quality in the scelp low delay audio codec (w-scelp)

Abstract: The SCELP (Spherical Code Excited Linear Prediction) audio codec, which has recently been proposed for low delay audio coding [5], is based on linear prediction (LP). It applies closed-loop vector quantization employing a spherical code which is based on the Apple Peeling code construction rule. Frequency warped signal processing is known to be beneficial especially in the context of wideband audio coding based on warped linear prediction (WLP). In this contribution, WLP is incorporated into the SCELP low delay audio codec. The overall audio quality of the resulting W-SCELP codec benefits from an improved perceptual masking of the quantization noise. Compared with existing standardized audio codecs with an algorithmic delay below 10 ms, the W-SCELP codec at a data rate of 48 kbit/sec outperforms the ITU-T G.722 codec at a data rate of 56 kbit/sec in terms of the achievable audio quality.

Telephone interface has digital speech processing

Abstract: Speech signals from a telephone are converted into digital form in unit 7 and the bit rate of the digital signals reduced by a coder, such as a CELP coder 8, so that an input speech passband of 100Hz to 4.8kHz (or wider) is carried by a digital signal of 20 kbit/s or less. This signal is then converted by a modulator 91 into a form which can be accommodated by a telephone line 2 having a passband of 300Hz to 3.8kHz. A corresponding demodulator 92 and decoder 16 are provided for the return path.

Signal Prediction by Pattern Search

Abstract: Prediction of a signal from earlier samples is widely used to reduce the information that must be transmitted for a suitably accurate reconstruction at a receiver. Linear prediction is a common means of effecting the prediction, but it does not accommodate well signals that include dominant innovations from time to time, as in the case of speech, or signals that are not well suited to modeling as the output of a linear dynamical system. We have investigated a scheme in which a set of recent samples is matched to an earlier set of samples and then the sample following the earlier set is used as the prediction. Error behavior is compared with linear prediction, theoretically and experimentally, and found to be reasonably similar on a mean square basis.