I've been looking into the Teensy Audio library for my project, and I need 4 FFT's running on 4 analog inputs in parallel. I'm concerned with latency, as what I'm doing more or less requires realtime response to changes in frequencies. I'm not sure what the latency of the current FFT is, but I noticed the only options are a 256-point and a 1024-point FFT. I'm concerned neither of these will be fast enough. I'm less concerned with resolution and more concerned with getting the response time down to a few milliseconds, if that's possible. I'm running on a Teensy 3.6 if that makes any difference.

Is it possible to modify the Teensy Audio library to add additional FFT objects of varying size, such as a 64-point FFT? Also, how would I calculate the length of time it takes the Teensy to finish processing one frame of data, depending on the number of points in the FFT?