Here i will first try to put my application agenda

Typically i am sampling at 8Khz rate and filtering speech components using a BPF(digital) now i have got the 0-4Khz components in which essentially <250Hz are not speech so i will eliminate them also now i am trying to find out entropy of frame and trying to mark respective frames as voice or non voice if they belong to band 250<=f<=3750 Hz

so now the problem is while i was doing this at my realtime application side there also non human sounds like birds sound or a ringing of a bell which again fall in to the frequency band i am flagging as speech

so this causes a false alarm of speech even in case of bird sound and bell ringing how to really over come this problem

what else i can try to do for effectvie speech activity detection

  • $\begingroup$ I suggest you to remove aliasing from the title of your question, since this phenomenon does not seem to be involved here. $\endgroup$ – pichenettes Sep 30 '13 at 8:35
  • $\begingroup$ if its not aliasing then what it is aliasing is when a high freq(greater than nyquist ) are been sampled, the components appear in existing band after the phenomenon of aliasing isn't it ? same seems to happening here a diff freq bird sound is appearing in speech region obviously looks aliasing for me $\endgroup$ – kakeh Sep 30 '13 at 9:09
  • 2
    $\begingroup$ You are correct about your definition of aliasing but this is not what is happening here. Birds or bell sounds simply do have frequency components in the 250-3750 Hz band. $\endgroup$ – pichenettes Sep 30 '13 at 9:10

This is not aliasing this is not any phenomenon, there are number of birds whose vocal fall in speech range even a frog vocal falls in speech range so essentially a training based speech detection is required to classify whether a given frame is speech or a non speech

one such implementation is shown here

Speech Discrimination based on multiscale spectro temporal modulations

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