Documentation 
Options for running filter output noise PSD
opts = noisepsdopts(H)
opts = noisepsdopts(H) uses the current settings in the dfilt object or the filter System object™, H, to create an options object, opts, that contains specified options for computing the output noise PSD. You can pass opts to the scale method as an input argument to apply scaling settings to a secondorder filter.
noisepsdopts returns the options object, opts, with which you can set the following properties for noisepsd:
Property Name  Default Value  Description and Valid Entries 

Nfft  512  Specify the number of FFT points to use to calculate the PSD. 
NormalizedFrequency  true  Determine whether to use normalized frequency. Enter a logical value of the logical true or false. Because this property is a logical value, and not a string, do not enclose with single quotation marks. 
Fs  normalized  Specify the sampling frequency to use when you set NormalizedFrequency to false. Use any integer value greater than 1. Enter the value in Hz. 
SpectrumType  onesided  Specify how noisepsd should generate the PSD. Options are onesided or twosided. If you choose a twosided computation, you can also choose centerdc = true. Otherwise, centerdc must be false.

CenterDC  false  Shift the zerofrequency component to the center of a twosided spectrum.

Arithmetic (only for filter System objects)  ARITH  Analyze the filter System object, based on the arithmetic specified in the ARITH input. ARITH can be set to double, single, or fixed. The analysis tool assumes a doubleprecision filter when the arithmetic input is not specified and the filter System object is in an unlocked state. 