Hello Sasha,
sincere apologies for the late reply: I've just digged your mail out
of ~2000 spam messages.
Concerning your issue with MakeTZX, I think I know what it is: an old bug! :-)
Unfortunately there's not much I can do today, because I'm not even
sure I still have the latest source code of MakeTZX. Man, it's been
ages since the last time I did something for the Spectrum scene!
If you really *have to* use our old program, please don't use
DirectMode sampling (-r switch) under Windows because it was buggy.
Sample the tape in your favourite format (e.g. WAV) using any
third-party sound recording software, and then process the file with MakeTZX.
Good luck with your TZX conversions!
Best regards,
Luca