ref: 39bf5b987e8ab53a74adec5a15b30f4eda85b357
dir: /sys/src/cmd/audio/libvorbis/scales.h/
/******************************************************************** * * * THIS FILE IS PART OF THE OggVorbis SOFTWARE CODEC SOURCE CODE. * * USE, DISTRIBUTION AND REPRODUCTION OF THIS LIBRARY SOURCE IS * * GOVERNED BY A BSD-STYLE SOURCE LICENSE INCLUDED WITH THIS SOURCE * * IN 'COPYING'. PLEASE READ THESE TERMS BEFORE DISTRIBUTING. * * * * THE OggVorbis SOURCE CODE IS (C) COPYRIGHT 1994-2009 * * by the Xiph.Org Foundation https://xiph.org/ * * * ******************************************************************** function: linear scale -> dB, Bark and Mel scales ********************************************************************/ #ifndef _V_SCALES_H_ #define _V_SCALES_H_ #include <math.h> #include "os.h" #ifdef _MSC_VER /* MS Visual Studio doesn't have C99 inline keyword. */ #define inline __inline #endif /* 20log10(x) */ #define VORBIS_IEEE_FLOAT32 1 #ifdef VORBIS_IEEE_FLOAT32 static inline float unitnorm(float x){ union { ogg_uint32_t i; float f; } ix; ix.f = x; ix.i = (ix.i & 0x80000000U) | (0x3f800000U); return ix.f; } /* Segher was off (too high) by ~ .3 decibel. Center the conversion correctly. */ static inline float todB(const float *x){ union { ogg_uint32_t i; float f; } ix; ix.f = *x; ix.i = ix.i&0x7fffffff; return (float)(ix.i * 7.17711438e-7f -764.6161886f); } #define todB_nn(x) todB(x) #else static float unitnorm(float x){ if(x<0)return(-1.f); return(1.f); } #define todB(x) (*(x)==0?-400.f:log(*(x)**(x))*4.34294480f) #define todB_nn(x) (*(x)==0.f?-400.f:log(*(x))*8.6858896f) #endif #define fromdB(x) (exp((x)*.11512925f)) /* The bark scale equations are approximations, since the original table was somewhat hand rolled. The below are chosen to have the best possible fit to the rolled tables, thus their somewhat odd appearance (these are more accurate and over a longer range than the oft-quoted bark equations found in the texts I have). The approximations are valid from 0 - 30kHz (nyquist) or so. all f in Hz, z in Bark */ #define toBARK(n) (13.1f*atan(.00074f*(n))+2.24f*atan((n)*(n)*1.85e-8f)+1e-4f*(n)) #define fromBARK(z) (102.f*(z)-2.f*pow(z,2.f)+.4f*pow(z,3.f)+pow(1.46f,z)-1.f) #define toMEL(n) (log(1.f+(n)*.001f)*1442.695f) #define fromMEL(m) (1000.f*exp((m)/1442.695f)-1000.f) /* Frequency to octave. We arbitrarily declare 63.5 Hz to be octave 0.0 */ #define toOC(n) (log(n)*1.442695f-5.965784f) #define fromOC(o) (exp(((o)+5.965784f)*.693147f)) #endif