50 lines
1.7 KiB
Plaintext
50 lines
1.7 KiB
Plaintext
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subroutine fil4(id1,n1,id2,n2)
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! FIR lowpass filter designed using ScopeFIR
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! fsample = 48000 Hz
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! Ntaps = 49
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! fc = 4500 Hz
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! fstop = 6000 Hz
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! Ripple = 1 dB
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! Stop Atten = 40 dB
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! fout = 12000 Hz
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parameter (NTAPS=49)
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parameter (NDOWN=4) !Downsample ratio
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integer*2 id1(n1)
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integer*2 id2(*)
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real t(NTAPS)
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data t/NTAPS*0.0/
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! Filter coefficients:
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real w(NTAPS)
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data w/ &
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0.000861074040, 0.010051920210, 0.010161983649, 0.011363155076, &
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0.008706594219, 0.002613872664,-0.005202883094,-0.011720748164, &
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-0.013752163325,-0.009431602741, 0.000539063909, 0.012636767098, &
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0.021494659597, 0.021951235065, 0.011564169382,-0.007656470131, &
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-0.028965787341,-0.042637874109,-0.039203309748,-0.013153301537, &
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0.034320769178, 0.094717832646, 0.154224604789, 0.197758325022, &
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0.213715139513, 0.197758325022, 0.154224604789, 0.094717832646, &
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0.034320769178,-0.013153301537,-0.039203309748,-0.042637874109, &
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-0.028965787341,-0.007656470131, 0.011564169382, 0.021951235065, &
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0.021494659597, 0.012636767098, 0.000539063909,-0.009431602741, &
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-0.013752163325,-0.011720748164,-0.005202883094, 0.002613872664, &
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0.008706594219, 0.011363155076, 0.010161983649, 0.010051920210, &
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0.000861074040/
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save w,t
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n2=n1/NDOWN
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if(n2*NDOWN.ne.n1) stop 'Error in fil4'
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k=1-NDOWN
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do i=1,n2
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k=k+NDOWN
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t(1:NTAPS-NDOWN)=t(1+NDOWN:NTAPS) !Shift old data down in array t
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t(1+NTAPS-NDOWN:NTAPS)=id1(k:k+NDOWN-1) !Insert new data at end of t
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id2(i)=nint(dot_product(w,t))
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enddo
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return
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end subroutine fil4
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