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annotate libtwamr/az_lsp.h @ 256:a33edf624061

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libgsmfr2: start with API definition and port of libgsmfrp code
author Mychaela Falconia <falcon@freecalypso.org>
date Fri, 12 Apr 2024 20:49:53 +0000
parents 54f6bc41ed10
children
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1 /*
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2 ********************************************************************************
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3 *
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4 * GSM AMR-NB speech codec R98 Version 7.6.0 December 12, 2001
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5 * R99 Version 3.3.0
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6 * REL-4 Version 4.1.0
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7 *
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8 ********************************************************************************
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9 *
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10 * File : az_lsp.h
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11 *
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12 ********************************************************************************
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13 */
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14 #ifndef az_lsp_h
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15 #define az_lsp_h "$Id $"
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16
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17 /*
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18 ********************************************************************************
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19 * INCLUDE FILES
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20 ********************************************************************************
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21 */
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22 #include "typedef.h"
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23
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24 /*
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25 ********************************************************************************
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26 * DEFINITION OF DATA TYPES
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27 ********************************************************************************
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28 */
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29
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30 /*
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31 ********************************************************************************
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32 * DECLARATION OF PROTOTYPES
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33 ********************************************************************************
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34 */
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35 /*
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36 **************************************************************************
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37 *
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38 * Function : Az_lsp
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39 * Purpose : Compute the LSPs from the LP coefficients
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40 * Description : - The sum and difference filters are computed
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41 * and divided by 1+z^{-1} and 1-z^{-1}, respectively.
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42 *
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43 * f1[i] = a[i] + a[11-i] - f1[i-1] ; i=1,...,5
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44 * f2[i] = a[i] - a[11-i] + f2[i-1] ; i=1,...,5
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45 *
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46 * - The roots of F1(z) and F2(z) are found using
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47 * Chebyshev polynomial evaluation. The polynomials
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48 * are evaluated at 60 points regularly spaced in the
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49 * frequency domain. The sign change interval is
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50 * subdivided 4 times to better track the root. The
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51 * LSPs are found in the cosine domain [1,-1].
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52 *
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53 * - If less than 10 roots are found, the LSPs from
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54 * the past frame are used.
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55 * Returns : void
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56 *
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57 **************************************************************************
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58 */
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59 void Az_lsp (
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60 Word16 a[], /* (i) : predictor coefficients (MP1) */
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61 Word16 lsp[], /* (o) : line spectral pairs (M) */
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62 Word16 old_lsp[] /* (i) : old lsp[] (in case not found 10 roots) (M)*/
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63 );
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64
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65 #endif