| Excitation codebook search method in a speech coding system -> Monitor Keywords |
|
|
  Excitation codebook search method in a speech coding systemUSPTO Application #: 20070043560Title: Excitation codebook search method in a speech coding system Abstract: A method for searching an excitation (or fixed) codebook in a speech coding system. In a speech coding system including a synthesis filter for synthesizing a speech signal, a fixed codebook searcher according to the present invention segments a speech signal frame into a plurality of subframes to generate an excitation signal to be used in a synthesis filter, segments again each of the subframes into a plurality of subgroups, and searches the respective subframes each comprised of a plurality of pulse position/amplitude combinations for pulses. The fixed codebook searcher searches the respective subgroups for a predetermine number of pulses having non-zero amplitude, and generates the searched pulses as an initial vector. Next, the fixed codebook searcher selects a pulse combination including at least one pulse among the pulses of the initial vector, and then substitutes pulses of the selected pulse combination for pulses in other positions in the subgroups. The selection and the substitution are repeatedly performed on all the pulses of the initial vector. (end of abstract)
Agent: Dilworth & Barrese, LLP - Uniondale, NY, US Inventor: Dae-Ryong Lee USPTO Applicaton #: 20070043560 - Class: 704219000 (USPTO) Related Patent Categories: Data Processing: Speech Signal Processing, Linguistics, Language Translation, And Audio Compression/decompression, Speech Signal Processing, For Storage Or Transmission, Linear Prediction The Patent Description & Claims data below is from USPTO Patent Application 20070043560. Brief Patent Description - Full Patent Description - Patent Application Claims
PRIORITY [0001] This application is a continuation of U.S. application Ser. No. 10/155,272, filed May 23, 2002, and claims priority to an application entitled "Excitation Codebook Search Method in a Speech Coding System" filed in the Korean Industrial Property Office on May 23, 2001 and assigned Serial No. 2001-28451, the contents of which are incorporated herein by reference. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates generally to a speech coding system, and in particular, to a method for searching an excitation codebook. [0004] 2. Description of the Related Art [0005] There are several types of vocoders, which compress speech signals. A vocoder typically used in a current mobile communication system is a CELP (Code Excited Linear Predictive coding) vocoder based on a liner prediction technique. The CELP vocoder is divided into a linear prediction filter for managing a linear prediction operation and a section for generating an excitation signal corresponding to an input signal from the linear prediction filter. Further, the CELP vocoder includes a pitch filter for modeling a pitch of the speech. Information on the pitch filter is collected through a so-called adaptive codebook search. A method for generating the excitation signal is classified into a method of using a created physical codebook and another method of calculating a code vector in algebra. The latter method is called "ACELP (Algebraic Code Excited Linear Predictive coding)". In the field of speech coding, a way to search for a code vector using the above two methods is referred to as a "codebook search". As an alternative concept of the adaptive codebook for searching for the information on the pitch filter, a codebook for searching for an excitation signal is called a "fixed codebook" or "excitation codebook". For example, a speech coding system using a physical codebook and a linear prediction filter is disclosed in detail in U.S. Pat. Nos. 3,624,302 and 4,701,954. [0006] The CELP technique using the physical codebook requires a large amount of memory and takes a great deal of time to search the codebook. Therefore, in most cases, the ACELP technique is used in the international standard for the vocoder. For example, a vocoder using the ACELP technique includes (i) EVRC (Enhanced Variable Rate Coding) used in a CDMA (Code Division Multiple Access) system, standardized by TIA/EIA/IS-127, EVRC and Speech Service Operation 3 for Wideband Spread Spectrum Digital Systems, and (ii) EFR (Enhanced Full Rate coding) chiefly used in a GSM (Global System for Mobile communication) mobile communication system, standardized by ESTI (European Telecommunication Standard Institute), disclosed in a paper entitled "GSM Enhanced Full Rate Speed Codec" K. Jarvinen et al. Proceedings ICASSP 1997 Intr'l Conf. [0007] The ACELP technique segments an excitation signal applied to the pitch filter and the linear prediction filter into several subgroups, and sets a specific condition that each subgroup has a predetermined number of pulses with non-zero amplitude. Also, the ACELP technique reduces the number of multiplications by attaching a condition that the pulse has an amplitude of "+1" or "-1", resulting in a remarkable reduction in a calculation time required for the codebook search. In addition, the ACELP technique separately codes the pulses in the respective subgroups before transmission, thereby preventing interference between the pulses in different subgroups. As a result, although a channel error occurs in several bits during transmission, the channel error affects only the pulses in the same subgroup and does not affect the pulses in the other subgroups. Thus, the ACELP technique is less susceptible to the channel environment. Compared with the ACELP technique, an LD-CELP (Low-Delay Code Excited Linear Predictive coding) technique using a stochastic codebook is susceptible to the channel error, since even a single-bit error of a codebook index affects the overall excitation signal. [0008] A process of searching a fixed codebook for a code vector by the CELP coding in order to search for an excitation signal will now be described herein below: [0009] The EFR or EVRC, a conventional ACELP technique, performs the code vector search process by segmenting an excitation signal with L samples into several subgroups and then searching for positions and amplitudes of a predetermined number of pulses in each subgroup in order to reduce calculations and secure insusceptibility to the channel environment. For example, as illustrated in Table 1, the EFR segments an excitation signal with L (=40) samples into 5 subgroups each having 8 samples, and searches for positions and amplitudes of a total of 10 pulses by searching for positions and amplitudes of 2 pulses in each subgroup. The positions of the pulses in the each subgroup are coded with 6 bits (i.e., 3 bits for each pulse), and the amplitudes of the pulses in each subgroup are fixed to "+1" or "-1". Here, a sign of 2 pulses in each subgroup is coded with 1 bit. As a result, an excitation signal is coded with a total of 35 bits (i.e., 7 bits for each subgroup). Whether amplitude of the pulses is "+1" or "-1" is calculated by referring to a residual of the linear prediction filter and a residual of the pitch filter in the positions of the respective pulses. TABLE-US-00001 TABLE 1 Subgroup Positions 0 0, 5, 10, 15, 20, 25, 30, 35 1 1, 6, 11, 16, 21, 26, 31, 36 2 2, 7, 12, 17, 22, 27, 32, 37 3 3, 8, 13, 18, 23, 28, 33, 42 4 4, 9, 14, 19, 24, 29, 34, 43 [0010] For the positions of the excitation pulses, it is necessary to search for a pulse position where an error, for which weighting between reference speech and synthetic speed obtained by passing positions and amplitudes of the possible pulses through a synthesis filter is taken into consideration, becomes minimized. When all of the pulse positions are taken into consideration, the number of searches becomes too large even on the assumption that the excitation signal is segmented into 5 subgroups and there are only 2 pulses in each subgroup. Therefore, the EFR uses the following suboptimal method. [0011] It will be assumed herein that the 10 pulse positions to be searched for are (m.sub.0, m.sub.1, . . . , m.sub.9). First, one pulse position is previously searched for in each of 5 tracks (subgroups). m.sub.0 will be situated in a position of a selected one of the 5 pulses and survive to the very end. Next, the repetitive operation is performed four times. In each repetitive operation, ml is fixed to the previously searched pulse position in the remaining 4 tracks. The remaining 8 pulses are searched for in pairs of (m.sub.2,m.sub.3), (m.sub.4,m.sub.5), (m.sub.6,m.sub.7), and (m.sub.8,m.sub.9), respectively. At each repetition, the start points of the 9 pulses are shifted in a circle. Therefore, the pulse pairs have different track combinations every repetition period. As a result, 2 of the 10 searched pulses belong to the 5 previously searched pulses. [0012] It should be noted herein that the applicant is interested in the fact that the EFR does not consider the effects of the remaining pulses m.sub.4, m.sub.5, . . . , m.sub.9 when searching for positions of the pulses (m.sub.2,m.sub.3). The calculation is performed in this way, because the pulses m.sub.4, m.sub.5, . . . , m.sub.9 were not searched for yet while searching for the pulses (m.sub.2,m.sub.3). However, whether this assumption is reasonable is uncertain. Instead, there is possibility that presuming even the remaining pulse positions will attain more reasonable results. [0013] As described above, the conventional ACELP technique uses a method of searching for the positions and amplitudes of the pulses.by stages. This method, however, increases calculations, so it is not possible to securely search for a code vector having a higher cost function value than the previously searched code vector, although the codebook is searched in various ways. SUMMARY OF THE INVENTION [0014] It is, therefore, an object of the present invention to provide a new codebook search method distinguishable from the conventional ACELP codebook search method, in order to resolve the problems of the ACELP codebook search. [0015] It is another object of the present invention to provide a codebook search method with improved coding performance in a speech coding system. [0016] To achieve the above and other objects, the present invention provides a new codebook search method. The codebook search method first searches for positions and amplitudes of a desired number of initial pulses, and then repeatedly exchanges the positions of or the positions and amplitudes of a predetermined number of pulses, thereby updating positions of new pulses. A cost function value calculated by the new codebook search method shows better results compared with the cost function value calculated by the conventional ACELP technique, resulting in an improvement in speech quality of a vocoder. BRIEF DESCRIPTION OF THE DRAWINGS [0017] The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which: [0018] FIG. 1 illustrates a block diagram of a conventional speech coding system to which the present invention is applied; [0019] FIG. 2 illustrates a procedure for performing an excitation codebook search operation according to a first embodiment of the present invention. [0020] FIG. 3 illustrates a procedure for performing an excitation codebook search operation according to a second embodiment of the present invention. Continue reading... Full patent description for Excitation codebook search method in a speech coding system Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Excitation codebook search method in a speech coding system patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Excitation codebook search method in a speech coding system or other areas of interest. ### Previous Patent Application: Adaptive reduction of noise signals and background signals in a speech-processing system Next Patent Application: Avoiding repeated misunderstandings in spoken dialog system Industry Class: Data processing: speech signal processing, linguistics, language translation, and audio compression/decompression ### FreshPatents.com Support Thank you for viewing the Excitation codebook search method in a speech coding system patent info. IP-related news and info Results in 0.45734 seconds Other interesting Feshpatents.com categories: Novartis , Pfizer , Philips , Polaroid , Procter & Gamble , |
||
