Oh, changing the filter definitely changes the timbre, but that's not what I meant. Even with a symmetric filter using only two values[0], there will still be an audible difference. The point of using the symmetric filter wasn't to get a more correct timbre, but to avoid changing the fundamental frequency.

Timbre is not the same as fundamental frequency. A guitar, a piano or a violin playing the same note, say, a middle C, will have wildly different timbres, but they should have the same fundamental frequency (261 Hz). That's what allows them to play together in orchestras. However, if you use, say 50 samples per buffer and a sample rate of 8192, with your original filter you won't get a frequency of 163.84 Hz, but 8192/49.5 = 165.49 Hz. That might look like a small difference, but to our ears it sounds wildly out of tune. You can use a tone analyzer app to verify it.

Thanks for the shout out :) I know I'm nitpicking :p

0: like for example, replacing with the average of the two surrounding values