ref: fcf95bac9330e8e6db1184496ae33007a7c7a9cf
dir: /src_common/SKP_Silk_LP_variable_cutoff.c/
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/*
Elliptic/Cauer filters designed with 0.1 dB passband ripple,
80 dB minimum stopband attenuation, and
[0.95 : 0.15 : 0.35] normalized cut off frequencies.
*/
#include "SKP_Silk_main.h"
/* Helper function, interpolates the filter taps */
SKP_INLINE void SKP_Silk_LP_interpolate_filter_taps(
SKP_int32 B_Q28[ TRANSITION_NB ],
SKP_int32 A_Q28[ TRANSITION_NA ],
const SKP_int ind,
const SKP_int32 fac_Q16
)
{
SKP_int nb, na;
if( ind < TRANSITION_INT_NUM - 1 ) {
if( fac_Q16 > 0 ) {
if( fac_Q16 < 32768 ) { /* fac_Q16 is in range of a 16-bit int */
/* Piece-wise linear interpolation of B and A */
for( nb = 0; nb < TRANSITION_NB; nb++ ) {
B_Q28[ nb ] = SKP_SMLAWB(
SKP_Silk_Transition_LP_B_Q28[ ind ][ nb ],
SKP_Silk_Transition_LP_B_Q28[ ind + 1 ][ nb ] -
SKP_Silk_Transition_LP_B_Q28[ ind ][ nb ],
fac_Q16 );
}
for( na = 0; na < TRANSITION_NA; na++ ) {
A_Q28[ na ] = SKP_SMLAWB(
SKP_Silk_Transition_LP_A_Q28[ ind ][ na ],
SKP_Silk_Transition_LP_A_Q28[ ind + 1 ][ na ] -
SKP_Silk_Transition_LP_A_Q28[ ind ][ na ],
fac_Q16 );
}
} else { /* ( fac_Q16 - ( 1 << 16 ) ) is in range of a 16-bit int */
SKP_assert( fac_Q16 - ( 1 << 16 ) == SKP_SAT16( fac_Q16 - ( 1 << 16 ) ) );
/* Piece-wise linear interpolation of B and A */
for( nb = 0; nb < TRANSITION_NB; nb++ ) {
B_Q28[ nb ] = SKP_SMLAWB(
SKP_Silk_Transition_LP_B_Q28[ ind + 1 ][ nb ],
SKP_Silk_Transition_LP_B_Q28[ ind + 1 ][ nb ] -
SKP_Silk_Transition_LP_B_Q28[ ind ][ nb ],
fac_Q16 - ( 1 << 16 ) );
}
for( na = 0; na < TRANSITION_NA; na++ ) {
A_Q28[ na ] = SKP_SMLAWB(
SKP_Silk_Transition_LP_A_Q28[ ind + 1 ][ na ],
SKP_Silk_Transition_LP_A_Q28[ ind + 1 ][ na ] -
SKP_Silk_Transition_LP_A_Q28[ ind ][ na ],
fac_Q16 - ( 1 << 16 ) );
}
}
} else {
SKP_memcpy( B_Q28, SKP_Silk_Transition_LP_B_Q28[ ind ], TRANSITION_NB * sizeof( SKP_int32 ) );
SKP_memcpy( A_Q28, SKP_Silk_Transition_LP_A_Q28[ ind ], TRANSITION_NA * sizeof( SKP_int32 ) );
}
} else {
SKP_memcpy( B_Q28, SKP_Silk_Transition_LP_B_Q28[ TRANSITION_INT_NUM - 1 ], TRANSITION_NB * sizeof( SKP_int32 ) );
SKP_memcpy( A_Q28, SKP_Silk_Transition_LP_A_Q28[ TRANSITION_INT_NUM - 1 ], TRANSITION_NA * sizeof( SKP_int32 ) );
}
}
/* Low-pass filter with variable cutoff frequency based on */
/* piece-wise linear interpolation between elliptic filters */
/* Start by setting psEncC->mode <> 0; */
/* Deactivate by setting psEncC->mode = 0; */
void SKP_Silk_LP_variable_cutoff(
SKP_Silk_LP_state *psLP, /* I/O LP filter state */
SKP_int16 *signal, /* I/O Low-pass filtered output signal */
const SKP_int frame_length /* I Frame length */
)
{
SKP_int32 B_Q28[ TRANSITION_NB ], A_Q28[ TRANSITION_NA ], fac_Q16 = 0;
SKP_int ind = 0;
SKP_assert( psLP->transition_frame_no >= 0 && psLP->transition_frame_no <= TRANSITION_FRAMES );
/* Interpolate filter coefficients if needed */
if( psLP->mode != 0 ) {
/* Calculate index and interpolation factor for interpolation */
#if( TRANSITION_INT_STEPS == 64 )
fac_Q16 = SKP_LSHIFT( TRANSITION_FRAMES - psLP->transition_frame_no, 16 - 6 );
#else
fac_Q16 = SKP_DIV32_16( SKP_LSHIFT( TRANSITION_FRAMES - psLP->transition_frame_no, 16 ), TRANSITION_FRAMES );
#endif
ind = SKP_RSHIFT( fac_Q16, 16 );
fac_Q16 -= SKP_LSHIFT( ind, 16 );
SKP_assert( ind >= 0 );
SKP_assert( ind < TRANSITION_INT_NUM );
/* Interpolate filter coefficients */
SKP_Silk_LP_interpolate_filter_taps( B_Q28, A_Q28, ind, fac_Q16 );
/* Update transition frame number for next frame */
psLP->transition_frame_no = SKP_LIMIT( psLP->transition_frame_no + psLP->mode, 0, TRANSITION_FRAMES );
/* ARMA low-pass filtering */
SKP_assert( TRANSITION_NB == 3 && TRANSITION_NA == 2 );
SKP_Silk_biquad_alt( signal, B_Q28, A_Q28, psLP->In_LP_State, signal, frame_length );
}
}