Having tried similar things myself, while autocorrelation looks useful for repeating waveforms, real waveforms at any point usually have more in common with the

Having tried similar things myself, while autocorrelation looks useful for repeating waveforms, real waveforms at any point usually have more in common with the preceding few samples than the same point in the previous cycle (e.g. Using LPC to predict the next sample based on the previous ones). One reason for this is the cycle length will usually not be a whole number of samples so you would have to interpolate between samples to find the same point in a previous cycle, and even then it's not an improvement over LPC.