freeswitch/libs/silk/src/SKP_Silk_VAD.c

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/*
 * File Name:   SKP_Silk_VAD.c
 * Description: Silk VAD.
 */

#include <stdlib.h>
#include "SKP_Silk_main.h"

/**********************************/
/* Initialization of the Silk VAD */
/**********************************/
SKP_int SKP_Silk_VAD_Init(                              /* O    Return value, 0 if success                  */
    SKP_Silk_VAD_state              *psSilk_VAD         /* I/O  Pointer to Silk VAD state                   */
)
{
    SKP_int b, ret = 0;

    /* reset state memory */
    SKP_memset( psSilk_VAD, 0, sizeof( SKP_Silk_VAD_state ) );

    /* init noise levels */
    /* Initialize array with approx pink noise levels (psd proportional to inverse of frequency) */
    for( b = 0; b < VAD_N_BANDS; b++ ) {
        psSilk_VAD->NoiseLevelBias[ b ] = SKP_max_32( SKP_DIV32_16( VAD_NOISE_LEVELS_BIAS, b + 1 ), 1 );
    }

    /* Initialize state */
    for( b = 0; b < VAD_N_BANDS; b++ ) {
        psSilk_VAD->NL[ b ]     = SKP_MUL( 100, psSilk_VAD->NoiseLevelBias[ b ] );
        psSilk_VAD->inv_NL[ b ] = SKP_DIV32( SKP_int32_MAX, psSilk_VAD->NL[ b ] );
    }
    psSilk_VAD->counter = 15;

    /* init smoothed energy-to-noise ratio*/
    for( b = 0; b < VAD_N_BANDS; b++ ) {
        psSilk_VAD->NrgRatioSmth_Q8[ b ] = 100 * 256;       /* 100 * 256 --> 20 dB SNR */
    }

    return( ret );
}

/* Weighting factors for tilt measure */
const static SKP_int32 tiltWeights[ VAD_N_BANDS ] = { 30000, 6000, -12000, -12000 };

/***************************************/
/* Get the speech activity level in Q8 */
/***************************************/
SKP_int SKP_Silk_VAD_GetSA_Q8(                                      /* O    Return value, 0 if success      */
    SKP_Silk_VAD_state              *psSilk_VAD,                    /* I/O  Silk VAD state                  */
    SKP_int                         *pSA_Q8,                        /* O    Speech activity level in Q8     */
    SKP_int                         *pSNR_dB_Q7,                    /* O    SNR for current frame in Q7     */
    SKP_int                         pQuality_Q15[ VAD_N_BANDS ],    /* O    Smoothed SNR for each band      */
    SKP_int                         *pTilt_Q15,                     /* O    current frame's frequency tilt  */
    const SKP_int16                 pIn[],                          /* I    PCM input       [framelength]   */
    const SKP_int                   framelength                     /* I    Input frame length              */
)
{
    SKP_int   SA_Q15, input_tilt;
    SKP_int32 scratch[ 3 * MAX_FRAME_LENGTH / 2 ];
    SKP_int   decimated_framelength, dec_subframe_length, dec_subframe_offset, SNR_Q7, i, b, s;
    SKP_int32 sumSquared, smooth_coef_Q16;
    SKP_int16 HPstateTmp;

    SKP_int16 X[ VAD_N_BANDS ][ MAX_FRAME_LENGTH / 2 ];
    SKP_int32 Xnrg[ VAD_N_BANDS ];
    SKP_int32 NrgToNoiseRatio_Q8[ VAD_N_BANDS ];
    SKP_int32 speech_nrg, x_tmp;
    SKP_int   ret = 0;

    /* Safety checks */
    SKP_assert( VAD_N_BANDS == 4 );
    SKP_assert( MAX_FRAME_LENGTH >= framelength );
    SKP_assert( framelength <= 512 );

    /***********************/
    /* Filter and Decimate */
    /***********************/
    /* 0-8 kHz to 0-4 kHz and 4-8 kHz */
    SKP_Silk_ana_filt_bank_1( pIn,          &psSilk_VAD->AnaState[  0 ], &X[ 0 ][ 0 ], &X[ 3 ][ 0 ], &scratch[ 0 ], framelength );

    /* 0-4 kHz to 0-2 kHz and 2-4 kHz */
    SKP_Silk_ana_filt_bank_1( &X[ 0 ][ 0 ], &psSilk_VAD->AnaState1[ 0 ], &X[ 0 ][ 0 ], &X[ 2 ][ 0 ], &scratch[ 0 ], SKP_RSHIFT( framelength, 1 ) );

    /* 0-2 kHz to 0-1 kHz and 1-2 kHz */
    SKP_Silk_ana_filt_bank_1( &X[ 0 ][ 0 ], &psSilk_VAD->AnaState2[ 0 ], &X[ 0 ][ 0 ], &X[ 1 ][ 0 ], &scratch[ 0 ], SKP_RSHIFT( framelength, 2 ) );

    /*********************************************/
    /* HP filter on lowest band (differentiator) */
    /*********************************************/
    decimated_framelength = SKP_RSHIFT( framelength, 3 );
    X[ 0 ][ decimated_framelength - 1 ] = SKP_RSHIFT( X[ 0 ][ decimated_framelength - 1 ], 1 );
    HPstateTmp = X[ 0 ][ decimated_framelength - 1 ];
    for( i = decimated_framelength - 1; i > 0; i-- ) {
        X[ 0 ][ i - 1 ]  = SKP_RSHIFT( X[ 0 ][ i - 1 ], 1 );
        X[ 0 ][ i ]     -= X[ 0 ][ i - 1 ];
    }
    X[ 0 ][ 0 ] -= psSilk_VAD->HPstate;
    psSilk_VAD->HPstate = HPstateTmp;

    /*************************************/
    /* Calculate the energy in each band */
    /*************************************/
    for( b = 0; b < VAD_N_BANDS; b++ ) {
        /* Find the decimated framelength in the non-uniformly divided bands */
        decimated_framelength = SKP_RSHIFT( framelength, SKP_min_int( VAD_N_BANDS - b, VAD_N_BANDS - 1 ) );

        /* Split length into subframe lengths */
        dec_subframe_length = SKP_RSHIFT( decimated_framelength, VAD_INTERNAL_SUBFRAMES_LOG2 );
        dec_subframe_offset = 0;

        /* Compute energy per sub-frame */
        /* initialize with summed energy of last subframe */
        Xnrg[ b ] = psSilk_VAD->XnrgSubfr[ b ];
        for( s = 0; s < VAD_INTERNAL_SUBFRAMES; s++ ) {
            sumSquared = 0;
            for( i = 0; i < dec_subframe_length; i++ ) {
                /* The energy will be less than dec_subframe_length * ( SKP_int16_MIN / 8 ) ^ 2.            */
                /* Therefore we can accumulate with no risk of overflow (unless dec_subframe_length > 128)  */
                x_tmp = SKP_RSHIFT( X[ b ][ i + dec_subframe_offset ], 3 );
                sumSquared = SKP_SMLABB( sumSquared, x_tmp, x_tmp );

                /* Safety check */
                SKP_assert( sumSquared >= 0 );
            }

            /* Add/saturate summed energy of current subframe */
            if( s < VAD_INTERNAL_SUBFRAMES - 1 ) {
                Xnrg[ b ] = SKP_ADD_POS_SAT32( Xnrg[ b ], sumSquared );
            } else {
                /* Look-ahead subframe */
                Xnrg[ b ] = SKP_ADD_POS_SAT32( Xnrg[ b ], SKP_RSHIFT( sumSquared, 1 ) );
            }

            dec_subframe_offset += dec_subframe_length;
        }
        psSilk_VAD->XnrgSubfr[ b ] = sumSquared;
    }

    /********************/
    /* Noise estimation */
    /********************/
    SKP_Silk_VAD_GetNoiseLevels( &Xnrg[ 0 ], psSilk_VAD );

    /***********************************************/
    /* Signal-plus-noise to noise ratio estimation */
    /***********************************************/
    sumSquared = 0;
    input_tilt = 0;
    for( b = 0; b < VAD_N_BANDS; b++ ) {
        speech_nrg = Xnrg[ b ] - psSilk_VAD->NL[ b ];
        if( speech_nrg > 0 ) {
            /* Divide, with sufficient resolution */
            if( ( Xnrg[ b ] & 0xFF800000 ) == 0 ) {
                NrgToNoiseRatio_Q8[ b ] = SKP_DIV32( SKP_LSHIFT( Xnrg[ b ], 8 ), psSilk_VAD->NL[ b ] + 1 );
            } else {
                NrgToNoiseRatio_Q8[ b ] = SKP_DIV32( Xnrg[ b ], SKP_RSHIFT( psSilk_VAD->NL[ b ], 8 ) + 1 );
            }

            /* Convert to log domain */
            SNR_Q7 = SKP_Silk_lin2log( NrgToNoiseRatio_Q8[ b ] ) - 8 * 128;

            /* Sum-of-squares */
            sumSquared = SKP_SMLABB( sumSquared, SNR_Q7, SNR_Q7 );          /* Q14 */

            /* Tilt measure */
            if( speech_nrg < ( 1 << 20 ) ) {
                /* Scale down SNR value for small subband speech energies */
                SNR_Q7 = SKP_SMULWB( SKP_LSHIFT( SKP_Silk_SQRT_APPROX( speech_nrg ), 6 ), SNR_Q7 );
            }
            input_tilt = SKP_SMLAWB( input_tilt, tiltWeights[ b ], SNR_Q7 );
        } else {
            NrgToNoiseRatio_Q8[ b ] = 256;
        }
    }

    /* Mean-of-squares */
    sumSquared = SKP_DIV32_16( sumSquared, VAD_N_BANDS ); /* Q14 */

    /* Root-mean-square approximation, scale to dBs, and write to output pointer */
    *pSNR_dB_Q7 = ( SKP_int16 )( 3 * SKP_Silk_SQRT_APPROX( sumSquared ) );  /* Q7 */

    /*********************************/
    /* Speech Probability Estimation */
    /*********************************/
    SA_Q15 = SKP_Silk_sigm_Q15( SKP_SMULWB( VAD_SNR_FACTOR_Q16, *pSNR_dB_Q7 ) - VAD_NEGATIVE_OFFSET_Q5 );

    /**************************/
    /* Frequency Tilt Measure */
    /**************************/
    *pTilt_Q15 = SKP_LSHIFT( SKP_Silk_sigm_Q15( input_tilt ) - 16384, 1 );

    /**************************************************/
    /* Scale the sigmoid output based on power levels */
    /**************************************************/
    speech_nrg = 0;
    for( b = 0; b < VAD_N_BANDS; b++ ) {
        /* Accumulate signal-without-noise energies, higher frequency bands have more weight */
        speech_nrg += ( b + 1 ) * SKP_RSHIFT( Xnrg[ b ] - psSilk_VAD->NL[ b ], 4 );
    }

    /* Power scaling */
    if( speech_nrg <= 0 ) {
        SA_Q15 = SKP_RSHIFT( SA_Q15, 1 );
    } else if( speech_nrg < 32768 ) {
        /* square-root */
        speech_nrg = SKP_Silk_SQRT_APPROX( SKP_LSHIFT( speech_nrg, 15 ) );
        SA_Q15 = SKP_SMULWB( 32768 + speech_nrg, SA_Q15 );
    }

    /* Copy the resulting speech activity in Q8 to *pSA_Q8 */
    *pSA_Q8 = SKP_min_int( SKP_RSHIFT( SA_Q15, 7 ), SKP_uint8_MAX );

    /***********************************/
    /* Energy Level and SNR estimation */
    /***********************************/
    /* Smoothing coefficient */
    smooth_coef_Q16 = SKP_SMULWB( VAD_SNR_SMOOTH_COEF_Q18, SKP_SMULWB( SA_Q15, SA_Q15 ) );
    for( b = 0; b < VAD_N_BANDS; b++ ) {
        /* compute smoothed energy-to-noise ratio per band */
        psSilk_VAD->NrgRatioSmth_Q8[ b ] = SKP_SMLAWB( psSilk_VAD->NrgRatioSmth_Q8[ b ],
            NrgToNoiseRatio_Q8[ b ] - psSilk_VAD->NrgRatioSmth_Q8[ b ], smooth_coef_Q16 );

        /* signal to noise ratio in dB per band */
        SNR_Q7 = 3 * ( SKP_Silk_lin2log( psSilk_VAD->NrgRatioSmth_Q8[b] ) - 8 * 128 );
        /* quality = sigmoid( 0.25 * ( SNR_dB - 16 ) ); */
        pQuality_Q15[ b ] = SKP_Silk_sigm_Q15( SKP_RSHIFT( SNR_Q7 - 16 * 128, 4 ) );
    }

    return( ret );
}

/**************************/
/* Noise level estimation */
/**************************/
void SKP_Silk_VAD_GetNoiseLevels(
    const SKP_int32                 pX[ VAD_N_BANDS ],  /* I    subband energies                            */
    SKP_Silk_VAD_state              *psSilk_VAD         /* I/O  Pointer to Silk VAD state                   */
)
{
    SKP_int   k;
    SKP_int32 nl, nrg, inv_nrg;
    SKP_int   coef, min_coef;

    /* Initially faster smoothing */
    if( psSilk_VAD->counter < 1000 ) { /* 1000 = 20 sec */
        min_coef = SKP_DIV32_16( SKP_int16_MAX, SKP_RSHIFT( psSilk_VAD->counter, 4 ) + 1 );
    } else {
        min_coef = 0;
    }

    for( k = 0; k < VAD_N_BANDS; k++ ) {
        /* Get old noise level estimate for current band */
        nl = psSilk_VAD->NL[ k ];
        SKP_assert( nl >= 0 );

        /* Add bias */
        nrg = SKP_ADD_POS_SAT32( pX[ k ], psSilk_VAD->NoiseLevelBias[ k ] );
        SKP_assert( nrg > 0 );

        /* Invert energies */
        inv_nrg = SKP_DIV32( SKP_int32_MAX, nrg );
        SKP_assert( inv_nrg >= 0 );

        /* Less update when subband energy is high */
        if( nrg > SKP_LSHIFT( nl, 3 ) ) {
            coef = VAD_NOISE_LEVEL_SMOOTH_COEF_Q16 >> 3;
        } else if( nrg < nl ) {
            coef = VAD_NOISE_LEVEL_SMOOTH_COEF_Q16;
        } else {
            coef = SKP_SMULWB( SKP_SMULWW( inv_nrg, nl ), VAD_NOISE_LEVEL_SMOOTH_COEF_Q16 << 1 );
        }

        /* Initially faster smoothing */
        coef = SKP_max_int( coef, min_coef );

        /* Smooth inverse energies */
        psSilk_VAD->inv_NL[ k ] = SKP_SMLAWB( psSilk_VAD->inv_NL[ k ], inv_nrg - psSilk_VAD->inv_NL[ k ], coef );
        SKP_assert( psSilk_VAD->inv_NL[ k ] >= 0 );

        /* Compute noise level by inverting again */
        nl = SKP_DIV32( SKP_int32_MAX, psSilk_VAD->inv_NL[ k ] );
        SKP_assert( nl >= 0 );

        /* Limit noise levels (guarantee 7 bits of head room) */
        nl = SKP_min( nl, 0x00FFFFFF );

        /* Store as part of state */
        psSilk_VAD->NL[ k ] = nl;
    }

    /* Increment frame counter */
    psSilk_VAD->counter++;
}