IDL Reference Guide: Procedures and Functions

BLK_CON

The BLK_CON function computes a "fast convolution" of a digital signal and an impulse-response sequence. It returns the filtered signal.

This routine is written in the IDL language. Its source code can be found in the file blk_con.pro in the lib subdirectory of the IDL distribution.

Syntax

Result = BLK_CON( Filter, Signal [, B_LENGTH=scalar] [, /DOUBLE] )

Return Value

This function returns a vector with the same length as Signal. If either of the input arguments are double-precision or the DOUBLE keyword is set, the result is double-precision, otherwise the result is single-precision.

Arguments

Filter

A P-element floating-point vector containing the impulse-response sequence of the digital filter.

Signal

An n-element floating-point vector containing the discrete signal samples.

Keywords

B_LENGTH

A scalar specifying the block length of the subdivided signal segments. If this parameter is not specified, a near-optimal value is chosen by the algorithm based upon the length P of the impulse-response sequence. If P is a value less than 11 or greater than 377, then B_LENGTH must be specified.

B_LENGTH must be greater than the filter length, P, and less than the number of signal samples.

DOUBLE

Set this keyword to force the computation to be done using double-precision arithmetic.

Examples

; Create a filter of length P = 32:  
filter = REPLICATE(1.0,32)   ;Set all points to 1.0  
filter(2*INDGEN(16)) = 0.5   ;Set even points to 0.5  
  
; Create a sampled signal with random noise:  
signal = SIN((FINDGEN(1000)/35.0)^2.5)  
noise = (RANDOMU(SEED,1000)-.5)/2.  
signal = signal + noise  
  
; Convolve the filter and signal using block convolution:  
result = BLK_CON(filter, signal)