fe_warp_piecewise_linear.c

/* -*- c-basic-offset: 4; indent-tabs-mode: nil -*- */
/* ====================================================================
 * Copyright (c) 2006 Carnegie Mellon University.  All rights 
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
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 * 1. Redistributions of source code must retain the above copyright
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 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * This work was supported in part by funding from the Defense Advanced 
 * Research Projects Agency and the National Science Foundation of the 
 * United States of America, and the CMU Sphinx Speech Consortium.
 *
 * THIS SOFTWARE IS PROVIDED BY CARNEGIE MELLON UNIVERSITY ``AS IS'' AND 
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/*********************************************************************
 *
 * File: fe_warp_piecewise_linear.c
 * 
 * Description: 
 *
 *      Warp the frequency axis according to an piecewise linear
 *      function. The function is linear up to a frequency F, where
 *      the slope changes so that the Nyquist frequency in the warped
 *      axis maps to the Nyquist frequency in the unwarped.
 *
 *              w' = a * w, w < F
 *              w' = a' * w + b, W > F
 *              w'(0) = 0
 *              w'(F) = F
 *              w'(Nyq) = Nyq
 *      
 *********************************************************************/

/* static char rcsid[] = "@(#)$Id: fe_warp_piecewise_linear.c,v 1.2 2006/02/17 00:31:34 egouvea Exp $"; */

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>

#ifdef _MSC_VER
#pragma warning (disable: 4996)
#endif

#include "sphinxbase/strfuncs.h"
#include "sphinxbase/err.h"

#include "fe_warp.h"
#include "fe_warp_piecewise_linear.h"

#define N_PARAM         2
#define YES             1
#define NO              0

/*
 * params[0] : a
 * params[1] : F (the non-differentiable point)
 */
static float params[N_PARAM] = { 1.0f, 6800.0f };
static float final_piece[2];
static int32 is_neutral = YES;
static char p_str[256] = "";
static float nyquist_frequency = 0.0f;


const char *
fe_warp_piecewise_linear_doc()
{
    return "piecewise_linear :== < w' = a * w, w < F >";
}

uint32
fe_warp_piecewise_linear_id()
{
    return FE_WARP_ID_PIECEWISE_LINEAR;
}

uint32
fe_warp_piecewise_linear_n_param()
{
    return N_PARAM;
}

void
fe_warp_piecewise_linear_set_parameters(char const *param_str,
                                        float sampling_rate)
{
    char *tok;
    char *seps = " \t";
    char temp_param_str[256];
    int param_index = 0;

    nyquist_frequency = sampling_rate / 2;
    if (param_str == NULL) {
        is_neutral = YES;
        return;
    }
    /* The new parameters are the same as the current ones, so do nothing. */
    if (strcmp(param_str, p_str) == 0) {
        return;
    }
    is_neutral = NO;
    strcpy(temp_param_str, param_str);
    memset(params, 0, N_PARAM * sizeof(float));
    memset(final_piece, 0, 2 * sizeof(float));
    strcpy(p_str, param_str);
    /* FIXME: strtok() is not re-entrant... */
    tok = strtok(temp_param_str, seps);
    while (tok != NULL) {
        params[param_index++] = (float) atof_c(tok);
        tok = strtok(NULL, seps);
        if (param_index >= N_PARAM) {
            break;
        }
    }
    if (tok != NULL) {
        E_INFO
            ("Piecewise linear warping takes up to two arguments, %s ignored.\n",
             tok);
    }
    if (params[1] < sampling_rate) {
        /* Precompute these. These are the coefficients of a
         * straight line that contains the points (F, aF) and (N,
         * N), where a = params[0], F = params[1], N = Nyquist
         * frequency.
         */
        if (params[1] == 0) {
            params[1] = sampling_rate * 0.85f;
        }
        final_piece[0] =
            (nyquist_frequency -
             params[0] * params[1]) / (nyquist_frequency - params[1]);
        final_piece[1] =
            nyquist_frequency * params[1] * (params[0] -
                                         1.0f) / (nyquist_frequency -
                                                  params[1]);
    }
    else {
        memset(final_piece, 0, 2 * sizeof(float));
    }
    if (params[0] == 0) {
        is_neutral = YES;
        E_INFO
            ("Piecewise linear warping cannot have slope zero, warping not applied.\n");
    }
}

float
fe_warp_piecewise_linear_warped_to_unwarped(float nonlinear)
{
    if (is_neutral) {
        return nonlinear;
    }
    else {
        /* linear = (nonlinear - b) / a */
        float temp;
        if (nonlinear < params[0] * params[1]) {
            temp = nonlinear / params[0];
        }
        else {
            temp = nonlinear - final_piece[1];
            temp /= final_piece[0];
        }
        if (temp > nyquist_frequency) {
            E_WARN
                ("Warp factor %g results in frequency (%.1f) higher than Nyquist (%.1f)\n",
                 params[0], temp, nyquist_frequency);
        }
        return temp;
    }
}

float
fe_warp_piecewise_linear_unwarped_to_warped(float linear)
{
    if (is_neutral) {
        return linear;
    }
    else {
        float temp;
        /* nonlinear = a * linear - b */
        if (linear < params[1]) {
            temp = linear * params[0];
        }
        else {
            temp = final_piece[0] * linear + final_piece[1];
        }
        return temp;
    }
}

void
fe_warp_piecewise_linear_print(const char *label)
{
    uint32 i;

    for (i = 0; i < N_PARAM; i++) {
        printf("%s[%04u]: %6.3f ", label, i, params[i]);
    }
    printf("\n");
}