CMSISDSP
Version 1.8.0
CMSIS DSP Software Library

Functions  
LOW_OPTIMIZATION_ENTER void  arm_biquad_cascade_df2T_f32 (const arm_biquad_cascade_df2T_instance_f32 *S, const float32_t *pSrc, float32_t *pDst, uint32_t blockSize) 
Processing function for the floatingpoint transposed direct form II Biquad cascade filter. More...  
LOW_OPTIMIZATION_ENTER void  arm_biquad_cascade_df2T_f64 (const arm_biquad_cascade_df2T_instance_f64 *S, const float64_t *pSrc, float64_t *pDst, uint32_t blockSize) 
Processing function for the floatingpoint transposed direct form II Biquad cascade filter. More...  
void  arm_biquad_cascade_df2T_init_f32 (arm_biquad_cascade_df2T_instance_f32 *S, uint8_t numStages, const float32_t *pCoeffs, float32_t *pState) 
Initialization function for the floatingpoint transposed direct form II Biquad cascade filter. More...  
void  arm_biquad_cascade_df2T_init_f64 (arm_biquad_cascade_df2T_instance_f64 *S, uint8_t numStages, const float64_t *pCoeffs, float64_t *pState) 
Initialization function for the floatingpoint transposed direct form II Biquad cascade filter. More...  
LOW_OPTIMIZATION_ENTER void  arm_biquad_cascade_stereo_df2T_f32 (const arm_biquad_cascade_stereo_df2T_instance_f32 *S, const float32_t *pSrc, float32_t *pDst, uint32_t blockSize) 
Processing function for the floatingpoint transposed direct form II Biquad cascade filter. More...  
void  arm_biquad_cascade_stereo_df2T_init_f32 (arm_biquad_cascade_stereo_df2T_instance_f32 *S, uint8_t numStages, const float32_t *pCoeffs, float32_t *pState) 
Initialization function for the floatingpoint transposed direct form II Biquad cascade filter. More...  
This set of functions implements arbitrary order recursive (IIR) filters using a transposed direct form II structure. The filters are implemented as a cascade of second order Biquad sections. These functions provide a slight memory savings as compared to the direct form I Biquad filter functions. Only floatingpoint data is supported.
This function operate on blocks of input and output data and each call to the function processes blockSize
samples through the filter. pSrc
points to the array of input data and pDst
points to the array of output data. Both arrays contain blockSize
values.
y[n] = b0 * x[n] + d1 d1 = b1 * x[n] + a1 * y[n] + d2 d2 = b2 * x[n] + a2 * y[n]where d1 and d2 represent the two state values.
b0, b1, and b2
multiply the input signal x[n]
and are referred to as the feedforward coefficients. Coefficients a1
and a2
multiply the output signal y[n]
and are referred to as the feedback coefficients. Pay careful attention to the sign of the feedback coefficients. Some design tools flip the sign of the feedback coefficients: y[n] = b0 * x[n] + d1; d1 = b1 * x[n]  a1 * y[n] + d2; d2 = b2 * x[n]  a2 * y[n];In this case the feedback coefficients
a1
and a2
must be negated when used with the CMSIS DSP Library. numStages
refers to the number of second order stages used. For example, an 8th order filter would be realized with numStages=4
second order stages. A 9th order filter would be realized with numStages=5
second order stages with the coefficients for one of the stages configured as a first order filter (b2=0
and a2=0
). pState
points to the state variable array. Each Biquad stage has 2 state variables d1
and d2
. The state variables are arranged in the pState
array as: {d11, d12, d21, d22, ...}where
d1x
refers to the state variables for the first Biquad and d2x
refers to the state variables for the second Biquad. The state array has a total length of 2*numStages
values. The state variables are updated after each block of data is processed; the coefficients are untouched. d1
and d2
. Because of this, the CMSIS library only has a floatingpoint version of the Direct Form II Biquad. The advantage of the Direct Form II Biquad is that it requires half the number of state variables, 2 rather than 4, per Biquad stage.arm_biquad_cascade_df2T_instance_f64 S1 = {numStages, pState, pCoeffs}; arm_biquad_cascade_df2T_instance_f32 S1 = {numStages, pState, pCoeffs};where
numStages
is the number of Biquad stages in the filter; pState
is the address of the state buffer. pCoeffs
is the address of the coefficient buffer; LOW_OPTIMIZATION_ENTER void arm_biquad_cascade_df2T_f32  (  const arm_biquad_cascade_df2T_instance_f32 *  S, 
const float32_t *  pSrc,  
float32_t *  pDst,  
uint32_t  blockSize  
) 
[in]  S  points to an instance of the filter data structure 
[in]  pSrc  points to the block of input data 
[out]  pDst  points to the block of output data 
[in]  blockSize  number of samples to process 
LOW_OPTIMIZATION_ENTER void arm_biquad_cascade_df2T_f64  (  const arm_biquad_cascade_df2T_instance_f64 *  S, 
const float64_t *  pSrc,  
float64_t *  pDst,  
uint32_t  blockSize  
) 
[in]  S  points to an instance of the filter data structure 
[in]  pSrc  points to the block of input data 
[out]  pDst  points to the block of output data 
[in]  blockSize  number of samples to process 
void arm_biquad_cascade_df2T_init_f32  (  arm_biquad_cascade_df2T_instance_f32 *  S, 
uint8_t  numStages,  
const float32_t *  pCoeffs,  
float32_t *  pState  
) 
[in,out]  S  points to an instance of the filter data structure. 
[in]  numStages  number of 2nd order stages in the filter. 
[in]  pCoeffs  points to the filter coefficients. 
[in]  pState  points to the state buffer. 
pCoeffs
in the following order in the not Neon version. {b10, b11, b12, a11, a12, b20, b21, b22, a21, a22, ...}
b1x
and a1x
are the coefficients for the first stage, b2x
and a2x
are the coefficients for the second stage, and so on. The pCoeffs
array contains a total of 5*numStages
values.For Neon version, this array is bigger. If numstages = 4x + y, then the array has size: 32*x + 5*y and it must be initialized using the function arm_biquad_cascade_df2T_compute_coefs_f32 which is taking the standard array coefficient as parameters.
But, an array of 8*numstages is a good approximation.
Then, the initialization can be done with:
arm_biquad_cascade_df2T_init_f32(&SNeon, nbCascade, neonCoefs, stateNeon); arm_biquad_cascade_df2T_compute_coefs_f32(&SNeon,nbCascade,coefs);
{b10, b11, b12, a11, a12, b20, b21, b22, a21, a22, ...}
pState
is a pointer to state array. Each Biquad stage has 2 state variables d1,
and d2
. The 2 state variables for stage 1 are first, then the 2 state variables for stage 2, and so on. The state array has a total length of 2*numStages
values. The state variables are updated after each block of data is processed; the coefficients are untouched. void arm_biquad_cascade_df2T_init_f64  (  arm_biquad_cascade_df2T_instance_f64 *  S, 
uint8_t  numStages,  
const float64_t *  pCoeffs,  
float64_t *  pState  
) 
[in,out]  S  points to an instance of the filter data structure 
[in]  numStages  number of 2nd order stages in the filter 
[in]  pCoeffs  points to the filter coefficients 
[in]  pState  points to the state buffer 
pCoeffs
in the following order: {b10, b11, b12, a11, a12, b20, b21, b22, a21, a22, ...}
b1x
and a1x
are the coefficients for the first stage, b2x
and a2x
are the coefficients for the second stage, and so on. The pCoeffs
array contains a total of 5*numStages
values. pState
is a pointer to state array. Each Biquad stage has 2 state variables d1,
and d2
. The 2 state variables for stage 1 are first, then the 2 state variables for stage 2, and so on. The state array has a total length of 2*numStages
values. The state variables are updated after each block of data is processed; the coefficients are untouched. LOW_OPTIMIZATION_ENTER void arm_biquad_cascade_stereo_df2T_f32  (  const arm_biquad_cascade_stereo_df2T_instance_f32 *  S, 
const float32_t *  pSrc,  
float32_t *  pDst,  
uint32_t  blockSize  
) 
Processing function for the floatingpoint transposed direct form II Biquad cascade filter. 2 channels.
[in]  S  points to an instance of the filter data structure 
[in]  pSrc  points to the block of input data 
[out]  pDst  points to the block of output data 
[in]  blockSize  number of samples to process 
void arm_biquad_cascade_stereo_df2T_init_f32  (  arm_biquad_cascade_stereo_df2T_instance_f32 *  S, 
uint8_t  numStages,  
const float32_t *  pCoeffs,  
float32_t *  pState  
) 
[in,out]  S  points to an instance of the filter data structure. 
[in]  numStages  number of 2nd order stages in the filter. 
[in]  pCoeffs  points to the filter coefficients. 
[in]  pState  points to the state buffer. 
pCoeffs
in the following order: {b10, b11, b12, a11, a12, b20, b21, b22, a21, a22, ...}
b1x
and a1x
are the coefficients for the first stage, b2x
and a2x
are the coefficients for the second stage, and so on. The pCoeffs
array contains a total of 5*numStages
values. pState
is a pointer to state array. Each Biquad stage has 2 state variables d1,
and d2
for each channel. The 2 state variables for stage 1 are first, then the 2 state variables for stage 2, and so on. The state array has a total length of 2*numStages
values. The state variables are updated after each block of data is processed; the coefficients are untouched.