opus/silk/resampler.c

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#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

/* Matrix of resampling methods used:
 *                                 Fs_out (kHz)
 *                        8      12     16     24    48
 *
 *               8        C      UF     U      UF     UF
 *              12        AF     C      UF     U      UF
 * Fs_in (kHz)  16        D      AF     C      UF     UF
 *              24        AIF    D      AF     C      U
 *              48        DAF    DAF    AF     D      C
 *
 * default method: UF
 *
 * C   -> Copy (no resampling)
 * D   -> Allpass-based 2x downsampling
 * U   -> Allpass-based 2x upsampling
 * DAF -> Allpass-based 2x downsampling followed by AR2 filter followed by FIR interpolation
 * UF  -> Allpass-based 2x upsampling followed by FIR interpolation
 * AF  -> AR2 filter followed by FIR interpolation
 *
 * Signals sampled above 48 kHz are not supported.
 */

#include "resampler_private.h"

#define USE_silk_resampler_copy                     (0)
#define USE_silk_resampler_private_up2_HQ_wrapper   (1)
#define USE_silk_resampler_private_IIR_FIR          (2)
#define USE_silk_resampler_private_down_FIR         (3)

/* Initialize/reset the resampler state for a given pair of input/output sampling rates */
opus_int silk_resampler_init(
    silk_resampler_state_struct *S,                 /* I/O   Resampler state                                            */
    opus_int32                  Fs_Hz_in,           /* I     Input sampling rate (Hz)                                   */
    opus_int32                  Fs_Hz_out           /* I     Output sampling rate (Hz)                                  */
)
{
    opus_int32 up2 = 0, down2 = 0;

    /* Clear state */
    silk_memset( S, 0, sizeof( silk_resampler_state_struct ) );

    /* Input checking */
    if( ( Fs_Hz_in  != 8000 && Fs_Hz_in  != 12000 && Fs_Hz_in  != 16000 && Fs_Hz_in  != 24000 && Fs_Hz_in  != 48000 ) ||
        ( Fs_Hz_out != 8000 && Fs_Hz_out != 12000 && Fs_Hz_out != 16000 && Fs_Hz_out != 24000 && Fs_Hz_out != 48000 ) ) {
        silk_assert( 0 );
        return -1;
    }

    /* Number of samples processed per batch */
    S->batchSize = silk_DIV32_16( Fs_Hz_in, 100 );

    /* Find resampler with the right sampling ratio */
    if( Fs_Hz_out > Fs_Hz_in ) {
        /* Upsample */
        if( Fs_Hz_out == silk_MUL( Fs_Hz_in, 2 ) ) {                            /* Fs_out : Fs_in = 2 : 1 */
            /* Special case: directly use 2x upsampler */
            S->resampler_function = USE_silk_resampler_private_up2_HQ_wrapper;
        } else {
            /* Default resampler */
            S->resampler_function = USE_silk_resampler_private_IIR_FIR;
            up2 = 1;
        }
    } else if ( Fs_Hz_out < Fs_Hz_in ) {
        /* Downsample */
        if( silk_MUL( Fs_Hz_out, 4 ) == silk_MUL( Fs_Hz_in, 3 ) ) {             /* Fs_out : Fs_in = 3 : 4 */
            S->FIR_Fracs = 3;
            S->Coefs = silk_Resampler_3_4_COEFS;
            S->resampler_function = USE_silk_resampler_private_down_FIR;
        } else if( silk_MUL( Fs_Hz_out, 3 ) == silk_MUL( Fs_Hz_in, 2 ) ) {      /* Fs_out : Fs_in = 2 : 3 */
            S->FIR_Fracs = 2;
            S->Coefs = silk_Resampler_2_3_COEFS;
            S->resampler_function = USE_silk_resampler_private_down_FIR;
        } else if( silk_MUL( Fs_Hz_out, 2 ) == Fs_Hz_in ) {                     /* Fs_out : Fs_in = 1 : 2 */
            S->FIR_Fracs = 1;
            S->Coefs = silk_Resampler_1_2_COEFS;
            S->resampler_function = USE_silk_resampler_private_down_FIR;
        } else if( silk_MUL( Fs_Hz_out, 3 ) == Fs_Hz_in ) {                     /* Fs_out : Fs_in = 1 : 3 */
            S->FIR_Fracs = 1;
            S->Coefs = silk_Resampler_1_3_COEFS;
            S->resampler_function = USE_silk_resampler_private_down_FIR;
        } else if( silk_MUL( Fs_Hz_out, 4 ) == Fs_Hz_in ) {                     /* Fs_out : Fs_in = 1 : 4 */
            S->FIR_Fracs = 1;
            down2 = 1;
            S->Coefs = silk_Resampler_1_2_COEFS;
            S->resampler_function = USE_silk_resampler_private_down_FIR;
        } else if( silk_MUL( Fs_Hz_out, 6 ) == Fs_Hz_in ) {                     /* Fs_out : Fs_in = 1 : 6 */
            S->FIR_Fracs = 1;
            down2 = 1;
            S->Coefs = silk_Resampler_1_3_COEFS;
            S->resampler_function = USE_silk_resampler_private_down_FIR;
        } else {
            /* None available */
            silk_assert( 0 );
            return -1;
        }
    } else {
        /* Input and output sampling rates are equal: copy */
        S->resampler_function = USE_silk_resampler_copy;
    }

    S->input2x = up2 | down2;

    /* Ratio of input/output samples */
    S->invRatio_Q16 = silk_LSHIFT32( silk_DIV32( silk_LSHIFT32( Fs_Hz_in, 14 + up2 - down2 ), Fs_Hz_out ), 2 );
    /* Make sure the ratio is rounded up */
    while( silk_SMULWW( S->invRatio_Q16, silk_LSHIFT32( Fs_Hz_out, down2 ) ) < silk_LSHIFT32( Fs_Hz_in, up2 ) ) {
        S->invRatio_Q16++;
    }

    return 0;
}

/* Resampler: convert from one sampling rate to another */
opus_int silk_resampler(
    silk_resampler_state_struct *S,                 /* I/O   Resampler state                                            */
    opus_int16                  out[],              /* O     Output signal                                              */
    const opus_int16            in[],               /* I     Input signal                                               */
    opus_int32                  inLen               /* I     Number of input samples                                    */
)
{
    /* Input and output sampling rate are at most 48000 Hz */
    switch( S->resampler_function ) {
        case USE_silk_resampler_private_up2_HQ_wrapper:
            silk_resampler_private_up2_HQ_wrapper( S, out, in, inLen );
            break;
        case USE_silk_resampler_private_IIR_FIR:
            silk_resampler_private_IIR_FIR( S, out, in, inLen );
            break;
        case USE_silk_resampler_private_down_FIR:
            silk_resampler_private_down_FIR( S, out, in, inLen );
            break;
        default:
            silk_memcpy( out, in, inLen * sizeof( opus_int16 ) );
    }
    return 0;
}