Output of FIR filter design methods is not compatible with functions that expects `FilterCoefficients`

[minecraft2048]

This works as expected:

responsetype = Lowpass(0.2)
designmethod = Elliptic(4, 0.5, 30)
coeffs = digitalfilter(responsetype, designmethod)
H,w = freqresp(coeffs)

but if I changed the designmethod to any FIR filter design methods, such as FIRWindow ,freqresp complains with MethodError: no method matching freqresp(::Vector{Float64}) :

responsetype = Lowpass(0.2)
designmethod = FIRWindow(hanning(64)) # <- changed here
coeffs = digitalfilter(responsetype, designmethod)
H,w = freqresp(coeffs) #breaks here

[mbaz]

This is a known issue, see for example #185

The workaround is to use

PolynomialRatio(coeffs, [1.0])

to convert the vector of coefficients to a filter type that DSP.jl recognizes.