Your lpcsynthesis_tilde_perform() method is simple and you've probably checked pointer arithmetic a dozen times. Yet valgrind attributes invalid reads and writes to it. How frustrating. Pd does not crash, the invalid access is probably happening within it's allocated space. Best thing would be if you can force Pd to crash on it. Instantiate a lot of your objects, delete some of them, or close/open patch several times etc. Pd's allocated memory is not a continuous block. Under circumstances, Pd must crash on an illegal access, and you'll be pointed to the culprit code. Well this is my not-so-educated guess. I've had similar situations with my own homebrew objects. Good luck anyway.