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/*
* 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;
}
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