You can measure shimmer in the Sound editor window, after choosing Show pulses from the **Pulses** menu. You will see blue lines that can be thought of as representing the glottal closures. Use the Pulse menu to get the shimmer in the selected part. You typically perform shimmer measurements only on long sustained vowels. The voice report gives six kinds of shimmer measurements.

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Shimmer (local)

This is the average absolute difference between the amplitudes of consecutive periods, divided by the average amplitude. MDVP calls this parameter *Shim*, and gives 3.810% as a threshold for pathology.

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Shimmer (local, dB)

This is the average absolute base-10 logarithm of the difference between the amplitudes of consecutive periods, multiplied by 20. MDVP calls this parameter *ShdB*, and gives 0.350 dB as a threshold for pathology.

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Shimmer (apq3)

This is the three-point Amplitude Perturbation Quotient, the average absolute difference between the amplitude of a period and the average of the amplitudes of its neighbours, divided by the average amplitude.

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Shimmer (apq5)

This is the five-point Amplitude Perturbation Quotient, the average absolute difference between the amplitude of a period and the average of the amplitudes of it and its four closest neighbours, divided by the average amplitude.

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Shimmer (apq11)

This is the 11-point Amplitude Perturbation Quotient, the average absolute difference between the amplitude of a period and the average of the amplitudes of it and its ten closest neighbours, divided by the average amplitude. MDVP calls this parameter *APQ*, and gives 3.070% as a threshold for pathology.

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Shimmer (ddp)

This is the average absolute difference between consecutive differences between the amplitudes of consecutive periods. This is Praat's original **Get shimmer**. The value is three times APQ3.

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© ppgb, May 21, 2003