Hi William,
As per my understanding, the output sequence after appyling the bandpass filter has a length different from that of the input sequence.
- Upsample the input data in the matrix xx_resamp by a factor of the integer p by inserting zeroes, where p is the upsampling factor.
- FIR filter the upsampled signal data with the impulse response sequence given in the vector or matrix bpf. This is a convolution operation.
- Downsample the result by a factor of the integer by throwing away samples, where q is the downsampling factor.
If the input is of length 
and the FIR filter is of length 
then the output in the step 2 will be of length 
(which happened in this case as well, since 172021 + 895 - 1 = 172915). The upsampling and downsampling factors for the function upfirdn is 1 by default, hence a workaround would be to change these values so that the output sequence has the desired length.
and the FIR filter is of length then the output in the step 2 will be of length (which happened in this case as well, since 172021 + 895 - 1 = 172915). The upsampling and downsampling factors for the function upfirdn is 1 by default, hence a workaround would be to change these values so that the output sequence has the desired length.Hope this helps!
