Fix another batch of bad strcmp post-merge

More bad strcmp calls after the commits for displaying the raw values
fed to subtrack2 were merged in
Fix retrieval of samples

After digging into the data that was being fed into the subtrack2
routine, it became clear that the data was nearly identical across all
three channels, except that it was shifted by what looked like a single
sample.

Turns out that _get_normalized_sample was missing the length of each
sample array so it was only adjusting the offset by the channel index,
rather than the channel index times the number of samples in the gather.

We are now getting clean separation out of the C code in the same way
that we get it from the Matlab code.