Transforms
[Basic]

Detailed Description

All the transforms functions currently supported by the DSP library.

Complex Fast Fourier Transform

This function computes a complex FFT from an input signal. It uses the Radix-4 "Decimate In Time" algorithm and does not perform a calculation "in place" which means that the input buffer has to be different from the output buffer.
Here is the formula of the FFT:
transforms_fft_equation.gif
Relative functions:

Complex inverse Fast Fourier Transform

This function computes a complex inverse FFT from an input signal. It uses the Radix-4 "Decimate In Time" algorithm and does not perform a calculation "in place" which means that the input buffer has to be different from the output buffer.
Here is the formula of the iFFT:
transforms_ifft_equation.gif
Relative functions:

Real to complex Fast Fourier Transform

This function computes a complex FFT from a real input signal. It uses the Radix-4 "Decimate In Time" algorithm and does not perform a calculation "in place" which means that the input buffer has to be different from the output buffer.
Here is the formula of the FFT:
transforms_fft_equation.gif
Relative functions:

Benchmark on the AT32UC targets


Functions

void dsp16_trans_complexfft (dsp16_complex_t *vect1, dsp16_complex_t *vect2, int nlog)
 16-bit fixed point version of the complex FFT algorithm.
void dsp16_trans_complexifft (dsp16_complex_t *vect1, dsp16_complex_t *vect2, int nlog)
 16-bit fixed point version of the complex iFFT algorithm.
void dsp16_trans_realcomplexfft (dsp16_complex_t *vect1, dsp16_t *vect2, int nlog)
 16-bit fixed point version of the real to complex FFT algorithm.
void dsp32_trans_realcomplexfft (dsp32_complex_t *vect1, dsp32_t *vect2, int nlog)
 32-bit fixed point version of the real to complex FFT algorithm.

Function Documentation

void dsp16_trans_complexfft ( dsp16_complex_t *  vect1,
dsp16_complex_t *  vect2,
int  nlog 
)

16-bit fixed point version of the complex FFT algorithm.

Parameters:
vect1 A pointer on a 16-bit complex vector which is the output buffer of this function.
vect2 A pointer on a 16-bit complex vector which is the input buffer of this function.
nlog It is the base-2-logarithm of the size of the input/output vector.
Due to its implementation, this function computes only 4^n-point complex FFT. Therefore, the nlog argument has to be even.
Note:
The following requirements have to be matched:
  • The size of the output buffer has to be the same as the size of the input buffer.
  • This function uses a static twiddle factors table which determines the maximal FFT size which can be performed. By default it is 1024. Please check the value of DSP16_N_TWIDDLE_FACTORS.
  • vect1 and vect2 MUST be 4-byte aligned. Please use A_ALIGNED to do so.
  • To avoid overflowing values, the resulting vector amplitude is scaled by 2^nlog.

void dsp16_trans_complexifft ( dsp16_complex_t *  vect1,
dsp16_complex_t *  vect2,
int  nlog 
)

16-bit fixed point version of the complex iFFT algorithm.

Parameters:
vect1 A pointer on a 16-bit complex vector which is the output buffer of this function.
vect2 A pointer on a 16-bit complex vector which is the input buffer of this function.
nlog It is the base-2-logarithm of the size of the input/output vector.
Due to its implementation, this function computes only 4^n-point complex iFFT. Therefore, the nlog argument has to be even.
Note:
The following requirements have to be matched:
  • The size of the output buffer has to be the same as the size of the input buffer.
  • This function uses a static twiddle factors table which determines the maximal FFT size which can be performed. By default it is 1024. Please check the value of DSP16_N_TWIDDLE_FACTORS.
  • vect1 and vect2 MUST be 4-byte aligned. Please use A_ALIGNED to do so.
  • To avoid overflowing values, the resulting vector amplitude is scaled by 2^nlog.

void dsp16_trans_realcomplexfft ( dsp16_complex_t *  vect1,
dsp16_t *  vect2,
int  nlog 
)

16-bit fixed point version of the real to complex FFT algorithm.

Parameters:
vect1 A pointer on a 16-bit complex vector which is the output buffer of this function.
vect2 A pointer on a 16-bit real vector which is the input buffer of this function.
nlog It is the base-2-logarithm of the size of the input/output vector.
Due to its implementation, this function computes only 4^n-point complex FFT. Therefore, the nlog argument has to be even.
Note:
The following requirements have to be matched:
  • The size of the output buffer has to be the same as the size of the input buffer.
  • This function uses a static twiddle factors table which determines the maximal FFT size which can be performed. By default it is 1024. Please check the value of DSP16_N_TWIDDLE_FACTORS.
  • vect1 and vect2 MUST be 4-byte aligned. Please use A_ALIGNED to do so.
  • To avoid overflowing values, the resulting vector amplitude is scaled by 2^nlog.

void dsp32_trans_realcomplexfft ( dsp32_complex_t *  vect1,
dsp32_t *  vect2,
int  nlog 
)

32-bit fixed point version of the real to complex FFT algorithm.

Parameters:
vect1 A pointer on a 32-bit complex vector which is the output buffer of this function.
vect2 A pointer on a 32-bit real vector which is the input buffer of this function.
nlog It is the base-2-logarithm of the size of the input/output vector.
Due to its implementation, this function computes only 4^n-point complex FFT. Therefore, the nlog argument has to be even.
Note:
The following requirements have to be matched:
  • The size of the output buffer has to be the same as the size of the input buffer.
  • This function uses a static twiddle factors table which determines the maximal FFT size which can be performed. By default it is 1024. Please check the value of DSP32_N_TWIDDLE_FACTORS.
  • vect1 and vect2 MUST be 4-byte aligned. Please use A_ALIGNED to do so.
  • To avoid overflowing values, the resulting vector amplitude is scaled by 2^nlog.

Generated on Thu Dec 17 20:00:32 2009 for AVR32 - Fixed point DSP Library by  doxygen 1.5.5