How do I estimate if in recorded sound samples is present an echo caused from walls reflection ? (maybe there are multiples echoes: delayed, attenuated versions of the signal itself).

I'm recording several sound samples in my room and I suppose that in the recorded audio samples is present an echo image of the original sound. How do I verify if this is true and in case, how can I calculate the samples delay (ms echo reflection time from the walls) ?

I plot the cross-correlation of the samples with itself (xcorr in MATLAB, about 40000 samples, ~1 second) but I don't know which pattern to look for to check if one or more echoes are present.


If I can understand the presence of the max peak in the middle of the graph, what are all the others equally spaced peaks on the both sides of the xcorr plot ? Eventually, how do I estimate the echo parameters from the recorderd samples (ms delay or samples delay) ?


2 Answers 2


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 & 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 & room size.


Try limiting the max lag of the xcorr based on the largest delay that you care about.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.