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Homework Help: Sound(Determine period, frequency from the plot)

  1. Jul 12, 2013 #1
    Hey, so I have this question
    Figure 1 shows a short duration segment of a speech waveform that has been sampled at 16,000 samples per second. The x-axis shows sample number, while the y-axis shows amplitude.


    (i) From the plot, is the speech signal voiced or unvoiced? State your rea- soning.
    (ii) From the plot, determine the number of samples that make up one period (or cycle) of the waveform.
    (iii) Hence, compute the pitch period of the waveform in seconds.
    (iv) Finally, compute the fundamental frequency (or pitch) of the speech sig-
    (v) Is this likely to come from a male or female talker - explain your reason-

    So I am not sure with my answers(i am stuck on iii):
    (ii) 70 samples per second. If i am right, i could say f_s = 70 Hz;
    (iii) I know the formula to find frequency (f =1/T), which I could use to find T, but is it possible to use it for f_s. if no,how can i find the period?
    (iv) I want to use formula from sampling theorem f_s = 2f Hz. In this case my fundamental frequency equals to 140Hz.

    As I said I am not sure of my solutions, so hope you can help me figure that out.
  2. jcsd
  3. Jul 12, 2013 #2
    Lets start with number i. An unvoised sound has no pitch to it. Think about saying "shut". The start of the word is a hiss not a frequency. Now think of the word "go" the sound of the "oo" has a pitch or frequency to it. So what do you think?

    Number ii is correct. However to get a good estimate, you should count the samples is say 4 cyles and then divide the number of samples by 4.

    On iii, if you know the sampling rate, it is given at 16000 samples per second and you have 70 samples between the wave popints, then what is the period of the tone? Knowing the period, you can easily compute the frequency, yes?

    As to male or female, female speakers usually have a higher frequency. However, I do not know what the threshold is.
  4. Jul 12, 2013 #3
    Thanks for the great reply, it really helped a lot.
    Just to check, I got the period - 0.004375s
  5. Jul 12, 2013 #4
    Now you can get the frequency and the problem is basically solved.
  6. Jul 12, 2013 #5
    Yeah, thanks a lot.
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