diff options
Diffstat (limited to 'media/libeffects/lvm/lib/Common/src/LVM_Mixer_TimeConstant.c')
| -rwxr-xr-x | media/libeffects/lvm/lib/Common/src/LVM_Mixer_TimeConstant.c | 165 |
1 files changed, 165 insertions, 0 deletions
diff --git a/media/libeffects/lvm/lib/Common/src/LVM_Mixer_TimeConstant.c b/media/libeffects/lvm/lib/Common/src/LVM_Mixer_TimeConstant.c new file mode 100755 index 0000000..db6975a --- /dev/null +++ b/media/libeffects/lvm/lib/Common/src/LVM_Mixer_TimeConstant.c @@ -0,0 +1,165 @@ +/* + * Copyright (C) 2004-2010 NXP Software + * Copyright (C) 2010 The Android Open Source Project + * + * Licensed under the Apache License, Version 2.0 (the "License"); + * you may not use this file except in compliance with the License. + * You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +/************************************************************************/ +/* */ +/* Project:: */ +/* $Author: beq07716 $*/ +/* $Revision: 1000 $*/ +/* $Date: 2010-06-28 13:08:20 +0200 (Mon, 28 Jun 2010) $*/ +/* */ +/************************************************************************/ + +#include "LVM_Types.h" +#include "LVM_Macros.h" +#include "Mixer.h" +#include "LVM_Mixer_FilterCoeffs.h" + + +/************************************************************************/ +/* FUNCTION: */ +/* LVM_Mix_GetTimeConstant */ +/* */ +/* DESCRIPTION: */ +/* This function calculates the filter coefficient using the following */ +/* equation: */ +/* Alpha = exp(ln(0.1)/ (tc * Update + 1.0)) */ +/* */ +/* This is to be used with the follow first order filter, called at a */ +/* rate of Update times a second. tc is the required time constant in */ +/* units of 100us. */ +/* */ +/* Output(n) = Alpha * Output(n-1) + (1 - Alpha) * Target(n) */ +/* */ +/* The function assumes the block size is large, i.e. the update rate */ +/* is approximately a fixed, and correct factor of the value of Fs */ +/* given in the call. This is especially not true when the block size */ +/* is very small, see the mixer documentation for further details. */ +/* */ +/* The function does not support all possible combinations of input */ +/* values: */ +/* */ +/* 1. NumChannels is limited to the values 1 (Mono) and 2 (Stereo) */ +/* 2. The product tc * Fs is limited approximately to the range */ +/* 8 < (tc * Fs) < 2^35 */ +/* */ +/* PARAMETERS: */ +/* tc - the time constant in 100us steps, i.e. 10 = 1ms */ +/* Fs - the filter update rate in Hz */ +/* NumChannels - Number of channels 1=Mono, 2=Stereo */ +/* */ +/* RETURNS: */ +/* Alpha - the filter coefficient Q31 format */ +/* */ +/************************************************************************/ + +LVM_UINT32 LVM_Mixer_TimeConstant(LVM_UINT32 tc, + LVM_UINT16 Fs, + LVM_UINT16 NumChannels) +{ + + LVM_UINT32 Product; + LVM_INT16 Interpolate; + LVM_UINT16 Shift; + LVM_INT32 Diff; + LVM_UINT32 Table[] = {ALPHA_0, /* Log spaced look-up table */ + ALPHA_1, + ALPHA_2, + ALPHA_3, + ALPHA_4, + ALPHA_5, + ALPHA_6, + ALPHA_7, + ALPHA_8, + ALPHA_9, + ALPHA_10, + ALPHA_11, + ALPHA_12, + ALPHA_13, + ALPHA_14, + ALPHA_15, + ALPHA_16, + ALPHA_17, + ALPHA_18, + ALPHA_19, + ALPHA_20, + ALPHA_21, + ALPHA_22, + ALPHA_23, + ALPHA_24, + ALPHA_25, + ALPHA_26, + ALPHA_27, + ALPHA_28, + ALPHA_29, + ALPHA_30, + ALPHA_31, + ALPHA_32, + ALPHA_33, + ALPHA_34, + ALPHA_35, + ALPHA_36, + ALPHA_37, + ALPHA_38, + ALPHA_39, + ALPHA_40, + ALPHA_41, + ALPHA_42, + ALPHA_43, + ALPHA_44, + ALPHA_45, + ALPHA_46, + ALPHA_47, + ALPHA_48, + ALPHA_49, + ALPHA_50}; + + + /* Calculate the product of the time constant and the sample rate */ + Product = ((tc >> 16) * (LVM_UINT32)Fs) << 13; /* Stereo value */ + Product = Product + (((tc & 0x0000FFFF) * (LVM_UINT32)Fs) >> 3); + + if (NumChannels == 1) + { + Product = Product >> 1; /* Mono value */ + } + + /* Normalize to get the table index and interpolation factor */ + for (Shift=0; Shift<((Alpha_TableSize-1)/2); Shift++) + { + if ((Product & 0x80000000)!=0) + { + break; + } + + Product = Product << 1; + } + Shift = (LVM_UINT16)((Shift << 1)); + + if ((Product & 0x40000000)==0) + { + Shift++; + } + + Interpolate = (LVM_INT16)((Product >> 15) & 0x00007FFF); + + Diff = (LVM_INT32)(Table[Shift] - Table[Shift+1]); + MUL32x16INTO32(Diff,Interpolate,Diff,15) + Product = Table[Shift+1] + (LVM_UINT32)Diff; + + return Product; +} |