Well, there is a heap, and to add or remove things from the heap takes time, and that time depends on the memory allocator algorithm used. I can totally see how it could affect audio streaming on really really slow hardware.
Ignoring everything else (as in - that wouldn't make a difference in practice due to the rate etc) - in this particular case, if you look at the posted code, the memory allocation was done a single time, so the issue as about sound quality when reading data from a buffer allocated (once) by malloc(), or by new().
