add conversion tables for AmbiX convention (edd73108) · Commits · IVAS Codec Public Collaboration / IVAS Codec

lib_util/ambi_convert.c

+36 −0

Original line number	Diff line number	Diff line
		@@ -55,6 +55,9 @@
		#define INV_SQRT_3_OVER_5_ 1.2909944f
		#define INV_SQRT_45_OVER_32_ 0.8432740f

		#define INV_SQRT_FOUR_PI_ 0.2820947f /* 1/sqrt(4/pi) */
		#define SQRT_FOUR_PI_ 3.5449077f

		#define AMBI_MAX_CHANNELS 16

		/* --------------------------------
		@@ -93,6 +96,23 @@ static const float FM_SN3D[AMBI_MAX_CHANNELS] = { INV_SQRT_2,
		INV_TWO_OVER_SQRT_3_, INV_TWO_OVER_SQRT_3_, 1.0f, INV_TWO_OVER_SQRT_3_, INV_TWO_OVER_SQRT_3_,
		INV_SQRT_8_OVER_5_, INV_SQRT_3_OVER_5_, INV_SQRT_45_OVER_32_, 1.0f, INV_SQRT_45_OVER_32_, INV_SQRT_3_OVER_5_, INV_SQRT_8_OVER_5_ };

		/*
		Curiously, not everyone seems to have the same understanding of what SN3D means. The Ambix paper
		(Nachbar et al. : AMBIX - A SUGGESTED AMBISONICS FORMAT) has an additional 1/sqrt(4*pi) in the
		normalization factor (see Eq. (3)) as compared to the tables in IVAS.
		*/

		static const float AMBIX_SN3D[AMBI_MAX_CHANNELS] = { INV_SQRT_FOUR_PI_,
		INV_SQRT_FOUR_PI_, INV_SQRT_FOUR_PI_, INV_SQRT_FOUR_PI_,
		INV_SQRT_FOUR_PI_, INV_SQRT_FOUR_PI_, INV_SQRT_FOUR_PI_, INV_SQRT_FOUR_PI_, INV_SQRT_FOUR_PI_,
		INV_SQRT_FOUR_PI_, INV_SQRT_FOUR_PI_, INV_SQRT_FOUR_PI_, INV_SQRT_FOUR_PI_, INV_SQRT_FOUR_PI_, INV_SQRT_FOUR_PI_, INV_SQRT_FOUR_PI_ };

		static const float SN3D_AMBIX[AMBI_MAX_CHANNELS] = { SQRT_FOUR_PI_,
		SQRT_FOUR_PI_, SQRT_FOUR_PI_, SQRT_FOUR_PI_,
		SQRT_FOUR_PI_, SQRT_FOUR_PI_, SQRT_FOUR_PI_, SQRT_FOUR_PI_, SQRT_FOUR_PI_,
		SQRT_FOUR_PI_, SQRT_FOUR_PI_, SQRT_FOUR_PI_, SQRT_FOUR_PI_, SQRT_FOUR_PI_, SQRT_FOUR_PI_, SQRT_FOUR_PI_ };


		/* ----------------------------
		channel re-ordering tables
		---------------------------- */
		@@ -136,6 +156,10 @@ int16_t convert_ambi_format( float in[], float out[], int16_t order, AMBI_FMT
		renormalize_channels( in, out, order, AMBI_NORM_SN3D, AMBI_NORM_MAXN );
		reorder_channels( in, out, order, AMBI_CHANNEL_ORDER_ACN, AMBI_CHANNEL_ORDER_FM );
		}
		else if ( out_format == AMBI_FMT_AMBIX )
		{
		renormalize_channels( in, out, order, AMBI_NORM_SN3D, AMBI_NORM_AMBIX );
		}
		else if ( out_format == AMBI_FMT_SID_SN3D )
		{
		reorder_channels( in, out, order, AMBI_CHANNEL_ORDER_ACN, AMBI_CHANNEL_ORDER_SID );
		@@ -161,6 +185,10 @@ int16_t convert_ambi_format( float in[], float out[], int16_t order, AMBI_FMT
		reorder_channels( in, out, order, AMBI_CHANNEL_ORDER_FM, AMBI_CHANNEL_ORDER_ACN );
		renormalize_channels( in, out, order, AMBI_NORM_MAXN, AMBI_NORM_SN3D );
		}
		else if ( in_format == AMBI_FMT_AMBIX )
		{
		renormalize_channels( in, out, order, AMBI_NORM_AMBIX, AMBI_NORM_SN3D );
		}
		else if ( in_format == AMBI_FMT_SID_SN3D )
		{
		reorder_channels( in, out, order, AMBI_CHANNEL_ORDER_SID, AMBI_CHANNEL_ORDER_ACN );
		@@ -201,6 +229,10 @@ int16_t renormalize_channels( float in[], float out[], int16_t order, AMBI_CHA
		{
		conversion_table = SN3D_MAXN;
		}
		else if ( out_format == AMBI_NORM_AMBIX )
		{
		conversion_table = SN3D_AMBIX;
		}
		else if ( out_format == AMBI_NORM_FM )
		{
		conversion_table = SN3D_FM;
		@@ -220,6 +252,10 @@ int16_t renormalize_channels( float in[], float out[], int16_t order, AMBI_CHA
		{
		conversion_table = MAXN_SN3D;
		}
		if ( in_format == AMBI_NORM_AMBIX )
		{
		conversion_table = AMBIX_SN3D;
		}
		else if ( in_format == AMBI_NORM_FM )
		{
		conversion_table = FM_SN3D;

lib_util/ambi_convert.h

+6 −4

Original line number	Diff line number	Diff line
		@@ -38,16 +38,18 @@
		typedef enum
		{
		AMBI_FMT_ACN_SN3D = 0,
		AMBI_FMT_ACN_N3D = 1,
		AMBI_FMT_FM_MAXN = 2,
		AMBI_FMT_SID_SN3D = 3,
		AMBI_FMT_SID_N3D = 4
		AMBI_FMT_ACN_N3D,
		AMBI_FMT_AMBIX,
		AMBI_FMT_FM_MAXN,
		AMBI_FMT_SID_SN3D,
		AMBI_FMT_SID_N3D
		} AMBI_FMT;

		typedef enum
		{
		AMBI_NORM_SN3D = 0,
		AMBI_NORM_N3D,
		AMBI_NORM_AMBIX,
		AMBI_NORM_MAXN,
		AMBI_NORM_FM
		} AMBI_CHANNEL_NORM;