src/earwax.c

   1 /* libSoX earwax - makes listening to headphones easier     November 9, 2000
   2  *
   3  * Copyright (c) 2000 Edward Beingessner And Sundry Contributors.
   4  * This source code is freely redistributable and may be used for any purpose.
   5  * This copyright notice must be maintained.  Edward Beingessner And Sundry
   6  * Contributors are not responsible for the consequences of using this
   7  * software.
   8  *
   9  * This effect takes a 44.1kHz stereo (CD format) signal that is meant to be
  10  * listened to on headphones, and adds audio cues to move the soundstage from
  11  * inside your head (standard for headphones) to outside and in front of the
  12  * listener (standard for speakers). This makes the sound much easier to listen
  13  * to on headphones.
  14  */
  15
  16 #include "sox_i.h"
  17 #include <string.h>
  18
  19 static const sox_sample_t filt[32 * 2] = {
  20 /* 30°  330° */
  21     4,   -6,     /* 32 tap stereo FIR filter. */
  22     4,  -11,     /* One side filters as if the */
  23    -1,   -5,     /* signal was from 30 degrees */
  24     3,    3,     /* from the ear, the other as */
  25    -2,    5,     /* if 330 degrees. */
  26    -5,    0,
  27     9,    1,
  28     6,    3,     /*                         Input                         */
  29    -4,   -1,     /*                   Left         Right                  */
  30    -5,   -3,     /*                __________   __________                */
  31    -2,   -5,     /*               |          | |          |               */
  32    -7,    1,     /*           .---|  Hh,0(f) | |  Hh,0(f) |---.           */
  33     6,   -7,     /*          /    |__________| |__________|    \          */
  34    30,  -29,     /*         /                \ /                \         */
  35    12,   -3,     /*        /                  X                  \        */
  36   -11,    4,     /*       /                  / \                  \       */
  37    -3,    7,     /*  ____V_____   __________V   V__________   _____V____  */
  38   -20,   23,     /* |          | |          |   |          | |          | */
  39     2,    0,     /* | Hh,30(f) | | Hh,330(f)|   | Hh,330(f)| | Hh,30(f) | */
  40     1,   -6,     /* |__________| |__________|   |__________| |__________| */
  41   -14,   -5,     /*      \     ___      /           \      ___     /      */
  42    15,  -18,     /*       \   /   \    /    _____    \    /   \   /       */
  43     6,    7,     /*        `->| + |<--'    /     \    `-->| + |<-'        */
  44    15,  -10,     /*           \___/      _/       \_      \___/           */
  45   -14,   22,     /*               \     / \       / \     /               */
  46    -7,   -2,     /*                `--->| |       | |<---'                */
  47    -4,    9,     /*                     \_/       \_/                     */
  48     6,  -12,     /*                                                       */
  49     6,   -6,     /*                       Headphones                      */
  50     0,  -11,
  51     0,   -5,
  52     4,    0};
  53
  54 #define NUMTAPS array_length(filt)
  55 typedef struct {sox_sample_t tap[NUMTAPS];} priv_t; /* FIR filter z^-1 delays */
  56
  57 static int start(sox_effect_t * effp)
  58 {
  59   priv_t * p = (priv_t *)effp->priv;
  60   if (effp->in_signal.rate != 44100 || effp->in_signal.channels != 2) {
  61     lsx_fail("works only with stereo audio sampled at 44100Hz (i.e. CDDA)");
  62     return SOX_EOF;
  63   }
  64   memset(p->tap, 0, NUMTAPS * sizeof(*p->tap)); /* zero tap memory */
  65   if (effp->in_signal.mult)
  66     *effp->in_signal.mult *= dB_to_linear(-4.4);
  67   return SOX_SUCCESS;
  68 }
  69
  70 static int flow(sox_effect_t * effp, const sox_sample_t * ibuf,
  71                 sox_sample_t * obuf, size_t * isamp, size_t * osamp)
  72 {
  73   priv_t * p = (priv_t *)effp->priv;
  74   size_t i, len = *isamp = *osamp = min(*isamp, *osamp);
  75
  76   while (len--) {       /* update taps and calculate output */
  77     double output = 0;
  78
  79     for (i = NUMTAPS - 1; i; --i) {
  80       p->tap[i] = p->tap[i - 1];
  81       output += p->tap[i] * filt[i];
  82     }
  83     p->tap[0] = *ibuf++ / 64; /* scale output */
  84     output += p->tap[0] * filt[0];
  85     *obuf++ = SOX_ROUND_CLIP_COUNT(output, effp->clips);
  86   }
  87   return SOX_SUCCESS;
  88 }
  89
  90 /* No drain: preserve audio file length; it's only 32 samples anyway. */
  91
  92 sox_effect_handler_t const *lsx_earwax_effect_fn(void)
  93 {
  94   static sox_effect_handler_t handler = {"earwax", NULL, SOX_EFF_MCHAN,
  95     NULL, start, flow, NULL, NULL, NULL, sizeof(priv_t)};
  96   return &handler;
  97 }