ref: 08eb1b8b27fcdf3d16d2641b0a256f25ef88b5b1
dir: /silk/LP_variable_cutoff.c/
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#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
/*
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 "main.h"
/* Helper function, interpolates the filter taps */
static OPUS_INLINE void silk_LP_interpolate_filter_taps(
opus_int32 B_Q28[ TRANSITION_NB ],
opus_int32 A_Q28[ TRANSITION_NA ],
const opus_int ind,
const opus_int32 fac_Q16
)
{
opus_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 ] = silk_SMLAWB(
silk_Transition_LP_B_Q28[ ind ][ nb ],
silk_Transition_LP_B_Q28[ ind + 1 ][ nb ] -
silk_Transition_LP_B_Q28[ ind ][ nb ],
fac_Q16 );
}
for( na = 0; na < TRANSITION_NA; na++ ) {
A_Q28[ na ] = silk_SMLAWB(
silk_Transition_LP_A_Q28[ ind ][ na ],
silk_Transition_LP_A_Q28[ ind + 1 ][ na ] -
silk_Transition_LP_A_Q28[ ind ][ na ],
fac_Q16 );
}
} else { /* ( fac_Q16 - ( 1 << 16 ) ) is in range of a 16-bit int */
silk_assert( fac_Q16 - ( 1 << 16 ) == silk_SAT16( fac_Q16 - ( 1 << 16 ) ) );
/* Piece-wise linear interpolation of B and A */
for( nb = 0; nb < TRANSITION_NB; nb++ ) {
B_Q28[ nb ] = silk_SMLAWB(
silk_Transition_LP_B_Q28[ ind + 1 ][ nb ],
silk_Transition_LP_B_Q28[ ind + 1 ][ nb ] -
silk_Transition_LP_B_Q28[ ind ][ nb ],
fac_Q16 - ( (opus_int32)1 << 16 ) );
}
for( na = 0; na < TRANSITION_NA; na++ ) {
A_Q28[ na ] = silk_SMLAWB(
silk_Transition_LP_A_Q28[ ind + 1 ][ na ],
silk_Transition_LP_A_Q28[ ind + 1 ][ na ] -
silk_Transition_LP_A_Q28[ ind ][ na ],
fac_Q16 - ( (opus_int32)1 << 16 ) );
}
}
} else {
silk_memcpy( B_Q28, silk_Transition_LP_B_Q28[ ind ], TRANSITION_NB * sizeof( opus_int32 ) );
silk_memcpy( A_Q28, silk_Transition_LP_A_Q28[ ind ], TRANSITION_NA * sizeof( opus_int32 ) );
}
} else {
silk_memcpy( B_Q28, silk_Transition_LP_B_Q28[ TRANSITION_INT_NUM - 1 ], TRANSITION_NB * sizeof( opus_int32 ) );
silk_memcpy( A_Q28, silk_Transition_LP_A_Q28[ TRANSITION_INT_NUM - 1 ], TRANSITION_NA * sizeof( opus_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 silk_LP_variable_cutoff(
silk_LP_state *psLP, /* I/O LP filter state */
opus_int16 *frame, /* I/O Low-pass filtered output signal */
const opus_int frame_length /* I Frame length */
)
{
opus_int32 B_Q28[ TRANSITION_NB ], A_Q28[ TRANSITION_NA ], fac_Q16 = 0;
opus_int ind = 0;
silk_assert( psLP->transition_frame_no >= 0 && psLP->transition_frame_no <= TRANSITION_FRAMES );
/* Run filter if needed */
if( psLP->mode != 0 ) {
/* Calculate index and interpolation factor for interpolation */
#if( TRANSITION_INT_STEPS == 64 )
fac_Q16 = silk_LSHIFT( TRANSITION_FRAMES - psLP->transition_frame_no, 16 - 6 );
#else
fac_Q16 = silk_DIV32_16( silk_LSHIFT( TRANSITION_FRAMES - psLP->transition_frame_no, 16 ), TRANSITION_FRAMES );
#endif
ind = silk_RSHIFT( fac_Q16, 16 );
fac_Q16 -= silk_LSHIFT( ind, 16 );
silk_assert( ind >= 0 );
silk_assert( ind < TRANSITION_INT_NUM );
/* Interpolate filter coefficients */
silk_LP_interpolate_filter_taps( B_Q28, A_Q28, ind, fac_Q16 );
/* Update transition frame number for next frame */
psLP->transition_frame_no = silk_LIMIT( psLP->transition_frame_no + psLP->mode, 0, TRANSITION_FRAMES );
/* ARMA low-pass filtering */
silk_assert( TRANSITION_NB == 3 && TRANSITION_NA == 2 );
silk_biquad_alt( frame, B_Q28, A_Q28, psLP->In_LP_State, frame, frame_length, 1);
}
}