Digital Signal Processing Reference
In-Depth Information
1.4
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Normalized Frequency
Figure 4.20:
The magnitude of frequency response at 500 frequency samples of the sequence [1.9, 0,
-0.9, 0, 1.9, 0, -3.2], estimated using cosine-sine correlator pairs at evenly spaced frequencies between 0
and 1.0, normalized frequency.
4.9.1 SINGLE CORRELATOR FILTERS OF ARBITRARY FREQUENCY
Any single-correlator filter of arbitrary length and center frequency can be generated with the following
call, where (for example) a length of 54, and normalized frequency of 9/27 = 0.333, have been chosen for
this particular experiment.
This results, using a cosine wave as the correlator in the following code, are shown in Fig. 4.21.
N=54;k=9;x=cos( 2*pi*k*( 0:1:N-1 )/ N );
LVFreqResp(x, 500)
4.9.2 MULTIPLE CORRELATOR FILTERS
To make a wider passband covering an arbitrary frequency range, adjacent single correlators can be
summed. Adjacent correlators must be 180 degrees out of phase. Note that the amplitude of correlators is
adjusted according to whether the frequency is 0,
N/
2, or otherwise, in accordance with our observations
made earlier in the chapter.
