How identify echo patterns in audio samples
The side peaks could be the result of periodic structure in your input signal (say around on the order of 8-10Hz, plus a 2nd harmonic).

If you are creating the sound samples, try playing pseudo-random noise, which has good autocorrelation properties for a long enough sample, notably tight peaks &amp; aperiodic.

2nd John's answer. You can do a back-of-the-envelope estimate of the max echo lag (assume a few reflections) using the speed of sound &amp; room size.