freeswitch/libs/silk/src/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"

#if SWITCH_TRANSITION_FILTERING

/* Helper function, that 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 == SKP_SAT16( fac_Q16 ) ) { /* 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 if( fac_Q16 == ( 1 << 15 ) ) { /* Neither fac_Q16 nor ( ( 1 << 16 ) - 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_RSHIFT(
                        SKP_Silk_Transition_LP_B_Q28[ ind     ][ nb ] +
                        SKP_Silk_Transition_LP_B_Q28[ ind + 1 ][ nb ],
                        1 );
                }
                for( na = 0; na < TRANSITION_NA; na++ ) {
                    A_Q28[ na ] = SKP_RSHIFT(
                        SKP_Silk_Transition_LP_A_Q28[ ind     ][ na ] +
                        SKP_Silk_Transition_LP_A_Q28[ ind + 1 ][ na ],
                        1 );
                }
            } else { /* ( ( 1 << 16 ) - fac_Q16 ) is in range of a 16-bit int */

                SKP_assert( ( ( 1 << 16 ) - fac_Q16 ) == SKP_SAT16( ( ( 1 << 16 ) - fac_Q16) ) );
                /* 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     ][ nb ] -
                        SKP_Silk_Transition_LP_B_Q28[ ind + 1 ][ nb ],
                        ( 1 << 16 ) - fac_Q16 );
                }
                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     ][ na ] -
                        SKP_Silk_Transition_LP_A_Q28[ ind + 1 ][ na ],
                        ( 1 << 16 ) - fac_Q16 );
                }
            }
        } 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->transition_frame_no = 1;            */
/* Deactivate by setting psEncC->transition_frame_no = 0;   */
void SKP_Silk_LP_variable_cutoff(
    SKP_Silk_LP_state               *psLP,          /* I/O  LP filter state                     */
    SKP_int16                       *out,           /* O    Low-pass filtered output signal     */
    const SKP_int16                 *in,            /* I    Input 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 );
    SKP_assert( ( ( ( psLP->transition_frame_no <= TRANSITION_FRAMES_DOWN ) && ( psLP->mode == 0 ) ) ||
                  ( ( psLP->transition_frame_no <= TRANSITION_FRAMES_UP   ) && ( psLP->mode == 1 ) ) ) );

    /* Interpolate filter coefficients if needed */
    if( psLP->transition_frame_no > 0 ) {
        if( psLP->mode == 0 ) {
            if( psLP->transition_frame_no < TRANSITION_FRAMES_DOWN ) {
                /* Calculate index and interpolation factor for interpolation */
#if( TRANSITION_INT_STEPS_DOWN == 32 )
                fac_Q16 = SKP_LSHIFT( psLP->transition_frame_no, 16 - 5 );
#else
                fac_Q16 = SKP_DIV32_16( SKP_LSHIFT( psLP->transition_frame_no, 16 ), TRANSITION_INT_STEPS_DOWN );
#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 );

                /* Increment transition frame number for next frame */
                psLP->transition_frame_no++;

            } else {
                SKP_assert( psLP->transition_frame_no == TRANSITION_FRAMES_DOWN );
                /* End of transition phase */
                SKP_Silk_LP_interpolate_filter_taps( B_Q28, A_Q28, TRANSITION_INT_NUM - 1, 0 );
            }
        } else {
            SKP_assert( psLP->mode == 1 );
            if( psLP->transition_frame_no < TRANSITION_FRAMES_UP ) {
                /* Calculate index and interpolation factor for interpolation */
#if( TRANSITION_INT_STEPS_UP == 64 )
                fac_Q16 = SKP_LSHIFT( TRANSITION_FRAMES_UP - psLP->transition_frame_no, 16 - 6 );
#else
                fac_Q16 = SKP_DIV32_16( SKP_LSHIFT( TRANSITION_FRAMES_UP - psLP->transition_frame_no, 16 ), TRANSITION_INT_STEPS_UP );
#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 );

                /* Increment transition frame number for next frame */
                psLP->transition_frame_no++;

            } else {
                SKP_assert( psLP->transition_frame_no == TRANSITION_FRAMES_UP );
                /* End of transition phase */
                SKP_Silk_LP_interpolate_filter_taps( B_Q28, A_Q28, 0, 0 );
            }
        }
    }

    if( psLP->transition_frame_no > 0 ) {
        /* ARMA low-pass filtering */
        SKP_assert( TRANSITION_NB == 3 && TRANSITION_NA == 2 );
        SKP_Silk_biquad_alt( in, B_Q28, A_Q28, psLP->In_LP_State, out, frame_length );
    } else {
        /* Instead of using the filter, copy input directly to output */
        SKP_memcpy( out, in, frame_length * sizeof( SKP_int16 ) );
    }
}
#endif