Note: This page has been translated by MathWorks. Please click here

To view all translated materals including this page, select Japan from the country navigator on the bottom of this page.

To view all translated materals including this page, select Japan from the country navigator on the bottom of this page.

Estimate empirical transfer functions and periodograms

estimates
a transfer function of the form:`g`

= etfe(`data`

)

`data`

contains time- or frequency-domain input-output
data or time-series data:

If

`data`

is time-domain input-output signals,`g`

is the ratio of the output Fourier transform to the input Fourier transform for the data.For nonperiodic data, the transfer function is estimated at 128 equally-spaced frequencies

`[1:128]/128*pi/Ts`

.For periodic data that contains a whole number of periods (

`data.Period = integer`

), the response is computed at the frequencies`k*2*pi/period`

for`k = 0`

up to the Nyquist frequency.If

`data`

is frequency-domain input-output signals,`g`

is the ratio of output to input at all frequencies, where the input is nonzero.If

`data`

is time-series data (no input channels),`g`

is the periodogram, that is the normed absolute square of the Fourier transform, of the data. The corresponding spectral estimate is normalized, as described in Spectrum Normalization and differs from the`spectrum`

normalization in the Signal Processing Toolbox™ product.

applies
a smoothing operation on the raw spectral estimates using a Hamming
Window that yields a frequency resolution of about `g`

= etfe(`data`

,`M`

)`pi/M`

.
The effect of `M`

is similar to the effect of `M`

in `spa`

. `M`

is ignored for
periodic data. Use this syntax as an alternative to `spa`

for
narrowband spectra and systems that require large values of `M`

.

specifies
the frequency spacing for nonperiodic data.`g`

= etfe(`data`

,`M`

,`N`

)

For nonperiodic time-domain data,

`N`

specifies the frequency grid`[1:N]/N*pi/Ts`

rad/TimeUnit. When not specified,`N`

is 128.For periodic time-domain data,

`N`

is ignored.For frequency-domain data, the

`N`

is`fmin:delta_f:fmax`

, where`[fmin fmax]`

is the range of frequencies in`data`

, and`delta_f`

is`(fmax-fmin)/(N-1)`

rad/TimeUnit. When not specified, the response is computed at the frequencies contained in data where input is nonzero.

Was this topic helpful?