# Uses of peaks in audio auto-correlation

Do you know of any algorithms for audio processing that make use of peaks in auto-correlation function? I am currently involved in research on mapping methodology for dynamic algorithms. I came recently over an algorithm for detection of fundamental frequency in audio signals, which has a dynamic structure I am looking for - the execution time of the algorithm varies with the number of peaks in the signal's auto-correlation:

while (i < hsize)

// Search for peaks in auto-correlation:
if((r[i] > 0) && (r[i]>r[i-1]) && (r[i]>=r[i+1])){

temp = 0.25f*(r[i+1]-r[i-1]);
temp = r[i] - temp*temp/(0.5f*(r[i+1]+r[i-1]) - r[i]);
n = n1[i] + n2[i];
if ((rmax*n) < (temp*nmax)) {imax=i; rmax=temp; nmax=n;}.

i++;}
else{i++;}


This would be perfect as a studying example for my methodology, but the problem is that there is only a couple of lines inside the loop, so the overhead of adding my techniques becomes too big for the problem of this size. Now I am wondering if there exist any similar algorithms in audio processing, i.e. also making use of peaks in auto-correlation function but perform more extensive calculations for each peak?

• Dear colleagues, I am sorry that my post do not have any greeting. I could actually not add any - it disappears from the posted text! Nov 25, 2014 at 9:46
• Elena, i would suggest that many pitch-detection algorithms use some form of auto-correlation and must look at every peak of any significance and make decisions regarding those peaks (like picking just one of the peaks and then interpolating the precise location). Nov 25, 2014 at 17:55
• Thank you Robert! This is a good hint, I will look closer at pitch-detection algorithms! Nov 26, 2014 at 9:04
• @ElenaHammari Greetings and thanks are automatically removed because they are considered a distraction from the question. Just ask the question and thank people by clicking the upvote arrows. Dec 26, 2014 at 15:36