I have created the following signal(in Matlab), a 5000 Hz sinusoid multiplied with a bump (just to limit it in time) so that it forms a short beep. Now if i observe the spectrum of this computationally created signal (in matlab) there is an impulse like structure at 5000Hz and nothing else.
Now i perform this experiment. I play this signal in matlab through a sound card into a speaker and record the sound played on the speaker through a microphone. The surprising thing is that if i observe the spectrum of this recorded signal, i find a impulse like structure at 5000Hz as expected but there is a another impulse like structure of much lower amplitude at 10000Hz and an even much smaller one at 15000Hz. I wonder how it can be explained.
When I repeated this experiment with 2000Hz I found same observation at 4000Hz and 8000Hz.