For all of my past SD projects I always rendered the audio using Dolby Digital AC-3 Pro but now that I'm learning about rendering HD projects I find some people recommending rendering the audio using Sony Wave 64. Which is considered better for HD audio and why?
It was just the way they address the container, so that you can have a very large file size. The recording format you put inside it is what matters. When you can record 192Khz@24bits, the file sizes climb fast.
AC3 is a delivery format specializing in compression, multi-track delivery, and tops out at 48Khz sample rate. Basically just another audio format that specifically licensed by Dolby Labs, mainly marketing designed to ride on THX and theater sound format PR.
Unless you are referring to 32FP or 64FP(double precision) audio. With Floating Point Audio in .w64, you get 32 channels, and the audio is written in a format that does not have the range limits that 16-24bit audio does.