ST_CM_Envelope_InitPars

Function block-specific structure with initialization parameters, which are analyzed when the function block is initialized.

TYPE ST_CM_Envelope_InitPars EXTENDS ST_CM_Object_InitPars :
STRUCT
    nFFT_Length    : UDINT := 512;    (* Length of FFT. *)
    nWindowLength  : UDINT := 400;    (* Length of analysis window. *)
    nChannels      : UDINT := 1;      (* Number of channels. *)
END_STRUCT
END_TYPE

• nFFT_Length is the length of the FFT. It must be greater than one and an integral power of two.
• nWindowLength is the length of the analysis window in samples. The length must be greater than one and an even number.
• nChannels defines the number of independent channels. This must be greater than zero.

Avoiding artefacts The value of nFFT_Length must be equal or greater the value of nWindowLength. In order to avoid artefacts in the calculation, nFFT_Length should be at least 25 larger than nWindowLength. An increase in the FFT length in relation to the window length makes sense with this function block in order to avoid circular aliasing.