diff --git a/src/Filters/filt.jl b/src/Filters/filt.jl
index efad5fe47..1833722b8 100644
--- a/src/Filters/filt.jl
+++ b/src/Filters/filt.jl
@@ -16,8 +16,7 @@ Same as [`filt()`](@ref) but writes the result into the `out`
 argument. Output array `out` may not be an alias of `x`, i.e. filtering may
 not be done in place.
 """
-filt!(out, f::PolynomialRatio{:z}, x::AbstractArray, si=_zerosi(f, x)) =
-    filt!(out, coefb(f), coefa(f), x, si)
+filt!(out, f::PolynomialRatio{:z}, x::AbstractArray, si...) = filt!(out, coefb(f), coefa(f), x, si...)
 
 """
     filt(f::FilterCoefficients{:z}, x::AbstractArray[, si])
@@ -32,7 +31,7 @@ to zeros). If `f` is a `PolynomialRatio`, `Biquad`, or
 interpreted as an FIR filter, and a naïve or FFT-based algorithm is
 selected based on the data and filter length.
 """
-filt(f::PolynomialRatio{:z}, x, si=_zerosi(f, x)) = filt(coefb(f), coefa(f), x, si)
+filt(f::PolynomialRatio{:z}, x, si...) = filt(coefb(f), coefa(f), x, si...)
 
 ## SecondOrderSections
 _zerosi(f::SecondOrderSections{:z,T,G}, ::AbstractArray{S}) where {T,G,S} =
@@ -58,8 +57,10 @@ function _filt!(out::AbstractArray, si::AbstractArray{S,N}, f::SecondOrderSectio
     si
 end
 
+filt!(out::AbstractArray, f::SecondOrderSections{:z}, x::AbstractArray) =
+    first(filt!(out, f, x, _zerosi(f, x)))
 function filt!(out::AbstractArray, f::SecondOrderSections{:z}, x::AbstractArray,
-                    si::AbstractArray{S,N}=_zerosi(f, x)) where {S,N}
+                    si::AbstractArray{S,N}) where {S,N}
     biquads = f.biquads
     ncols = Base.trailingsize(x, 2)
 
@@ -67,17 +68,19 @@ function filt!(out::AbstractArray, f::SecondOrderSections{:z}, x::AbstractArray,
     (size(si, 1) != 2 || size(si, 2) != length(biquads) || (N > 2 && Base.trailingsize(si, 3) != ncols)) &&
         throw(ArgumentError("si must be 2 x nbiquads or 2 x nbiquads x nsignals"))
 
-    initial_si = si
-    si = similar(si, axes(si)[1:2])
+    if N > 2
+        si = copy(si)
+    else
+        si = repeat(si, outer=(1, 1, size(x)[2:end]...))
+    end
     for col in CartesianIndices(axes(x)[2:end])
-        copyto!(si, view(initial_si, :, :, N > 2 ? col : 1))
-        _filt!(out, si, f, x, col)
+        _filt!(out, view(si, :, :, col), f, x, col)
     end
-    out
+    return (out, si)
 end
 
-filt(f::SecondOrderSections{:z,T,G}, x::AbstractArray{S}, si=_zerosi(f, x)) where {T,G,S<:Number} =
-    filt!(similar(x, promote_type(T, G, S)), f, x, si)
+filt(f::SecondOrderSections{:z,T,G}, x::AbstractArray{S}, si...) where {T,G,S<:Number} =
+    filt!(similar(x, promote_type(T, G, S)), f, x, si...)
 
 ## Biquad
 _zerosi(::Biquad{:z,T}, ::AbstractArray{S}) where {T,S} =
@@ -96,27 +99,34 @@ function _filt!(out::AbstractArray, si1::Number, si2::Number, f::Biquad{:z},
     (si1, si2)
 end
 
+filt!(out::AbstractArray, f::Biquad{:z}, x::AbstractArray) =
+    first(filt!(out, f, x, _zerosi(f, x)))
 # filt! variant that preserves si
 function filt!(out::AbstractArray, f::Biquad{:z}, x::AbstractArray,
-                    si::AbstractArray{S,N}=_zerosi(f, x)) where {S,N}
+                    si::AbstractArray{S,N}) where {S,N}
     ncols = Base.trailingsize(x, 2)
 
     size(x) != size(out) && throw(DimensionMismatch("out size must match x"))
     (size(si, 1) != 2 || (N > 1 && Base.trailingsize(si, 2) != ncols)) &&
         throw(ArgumentError("si must have two rows and 1 or nsignals columns"))
 
+    if N > 1
+        si = copy(si)
+    else
+        si = repeat(si, outer=(1, size(x)[2:end]...))
+    end
     for col in CartesianIndices(axes(x)[2:end])
-        _filt!(out, si[1, N > 1 ? col : 1], si[2, N > 1 ? col : 1], f, x, col)
+        si[:,col] .= _filt!(out, si[1, col], si[2, col], f, x, col)
     end
-    out
+    return (out, si)
 end
 
-filt(f::Biquad{:z,T}, x::AbstractArray{S}, si=_zerosi(f, x)) where {T,S<:Number} =
-    filt!(similar(x, promote_type(T, S)), f, x, si)
+filt(f::Biquad{:z,T}, x::AbstractArray{S}, si...) where {T,S<:Number} =
+    filt!(similar(x, promote_type(T, S)), f, x, si...)
 
 ## For arbitrary filters, convert to SecondOrderSections
-filt(f::FilterCoefficients{:z}, x) = filt(convert(SecondOrderSections, f), x)
-filt!(out, f::FilterCoefficients{:z}, x) = filt!(out, convert(SecondOrderSections, f), x)
+filt(f::FilterCoefficients{:z}, x, si...) = filt(convert(SecondOrderSections, f), x, si...)
+filt!(out, f::FilterCoefficients{:z}, x, si...) = filt!(out, convert(SecondOrderSections, f), x, si...)
 
 """
     DF2TFilter(coef::FilterCoefficients{:z}[, si])
@@ -353,7 +363,7 @@ function filtfilt(f::SecondOrderSections{:z,T,G}, x::AbstractArray{S}) where {T,
     istart = 1
     for i = 1:Base.trailingsize(x, 2)
         extrapolate_signal!(extrapolated, 1, x, istart, size(x, 1), pad_length)
-        reverse!(filt!(extrapolated, f, extrapolated, mul!(zitmp, zi, extrapolated[1])))
+        reverse!(first(filt!(extrapolated, f, extrapolated, mul!(zitmp, zi, extrapolated[1]))))
         filt!(extrapolated, f, extrapolated, mul!(zitmp, zi, extrapolated[1]))
         for j = 1:size(x, 1)
             @inbounds out[j, i] = extrapolated[end-pad_length+1-j]
diff --git a/src/dspbase.jl b/src/dspbase.jl
index 23f71579c..55e1d94ea 100644
--- a/src/dspbase.jl
+++ b/src/dspbase.jl
@@ -16,7 +16,11 @@ state vector `si` (defaults to zeros).
 Inputs that are `Number`s are treated as one-element `Vector`s.
 """
 function filt(b::Union{AbstractVector, Number}, a::Union{AbstractVector, Number},
-              x::AbstractArray{T}, si::AbstractArray{S} = _zerosi(b,a,T)) where {T,S}
+              x::AbstractArray{T}) where {T}
+    first(filt(b, a, x, _zerosi(b,a,T)))
+end
+function filt(b::Union{AbstractVector, Number}, a::Union{AbstractVector, Number},
+    x::AbstractArray{T}, si::AbstractArray{S}) where {T,S}
     filt!(similar(x, promote_type(eltype(b), eltype(a), T, S)), b, a, x, si)
 end
 
@@ -29,8 +33,11 @@ end
 Same as [`filt`](@ref) but writes the result into the `out` argument, which may
 alias the input `x` to modify it in-place.
 """
+filt!(out::AbstractArray, b::Union{AbstractVector, Number}, a::Union{AbstractVector, Number},
+    x::AbstractArray{T}) where {T} =
+    first(filt!(out, b, a, x, _zerosi(b,a,T)))
 function filt!(out::AbstractArray, b::Union{AbstractVector, Number}, a::Union{AbstractVector, Number},
-               x::AbstractArray{T}, si::AbstractArray{S,N} = _zerosi(b,a,T)) where {T,S,N}
+               x::AbstractArray{T}, si::AbstractArray{S,N}) where {T,S,N}
     isempty(b) && throw(ArgumentError("filter vector b must be non-empty"))
     isempty(a) && throw(ArgumentError("filter vector a must be non-empty"))
     a[1] == 0  && throw(ArgumentError("filter vector a[1] must be nonzero"))
@@ -42,16 +49,25 @@ function filt!(out::AbstractArray, b::Union{AbstractVector, Number}, a::Union{Ab
     bs = length(b)
     sz = max(as, bs)
     silen = sz - 1
-    ncols = size(x, 2)
+    ncols = prod(size(x)[2:end]; init=1)
 
     if size(si, 1) != silen
         throw(ArgumentError("initial state vector si must have max(length(a),length(b))-1 rows"))
-    elseif N > 1 && size(si, 2) != ncols
+    elseif N > 1 && size(si)[2:end] != size(x)[2:end]
         throw(ArgumentError("initial state si must be a vector or have the same number of columns as x"))
     end
 
-    iszero(size(x, 1)) && return out
-    isone(sz) && return (k = b[1] / a[1]; @noinline mul!(out, x, k)) # Simple scaling without memory
+    if N > 1
+        si = copy(si)
+    else
+        si = repeat(si, outer=(1, size(x)[2:end]...))
+    end
+
+    iszero(size(x, 1)) && return (out, si)
+    if isone(sz)
+        k = b[1] / a[1]
+        return (@noinline mul!(out, x, k), si) # Simple scaling without memory
+    end
 
     # Filter coefficient normalization
     if !isone(a[1])
@@ -66,19 +82,15 @@ function filt!(out::AbstractArray, b::Union{AbstractVector, Number}, a::Union{Ab
     if as == 1 && bs <= SMALL_FILT_CUTOFF
         _small_filt_fir!(out, b, x, si, Val(bs))
     else
-        initial_si = si
-        si = similar(si, axes(si, 1))
         for col in CartesianIndices(axes(x)[2:end])
-            # Reset the filter state
-            copyto!(si, view(initial_si, :, N > 1 ? col : 1))
             if as > 1
-                _filt_iir!(out, b, a, x, si, col)
+                _filt_iir!(out, b, a, x, view(si, :, col), col)
             else
-                _filt_fir!(out, b, x, si, col)
+                _filt_fir!(out, b, x, view(si, :, col), col)
             end
         end
     end
-    return out
+    return (out, si)
 end
 
 # Transposed direct form II
@@ -143,12 +155,12 @@ end
 # Convert array filter tap input to tuple for small-filtering
 function _small_filt_fir!(
     out::AbstractArray, h::AbstractVector, x::AbstractArray,
-        si::AbstractArray{S,N}, ::Val{bs}) where {S,N,bs}
+        si::AbstractArray, ::Val{bs}) where {bs}
 
     bs < 2 && throw(ArgumentError("invalid tuple size"))
     b = ntuple(j -> @inbounds(h[j]), Val(bs))
     for col in axes(x, 2)
-        v_si = view(si, :, N > 1 ? col : 1)
+        v_si = view(si, :, col)
         _filt_fir!(out, b, x, v_si, col)
     end
 end
diff --git a/test/dsp.jl b/test/dsp.jl
index 610b44bc4..6aee88937 100644
--- a/test/dsp.jl
+++ b/test/dsp.jl
@@ -20,16 +20,16 @@ using DSP: filt, filt!, deconv, conv, xcorr,
     @test filt(b, 1., [x 1.0:8.0]) == [filt(b, 1., x) filt(b, 1., 1.0:8.0)]
     @test filt(b, [1., -0.5], [x 1.0:8.0]) == [filt(b, [1., -0.5], x) filt(b, [1., -0.5], 1.0:8.0)]
     si = zeros(3)
-    @test filt(b, 1., [x 1.0:8.0], si) == [filt(b, 1., x, si) filt(b, 1., 1.0:8.0, si)]
+    @test first(filt(b, 1., [x 1.0:8.0], si)) == [first(filt(b, 1., x, si)) first(filt(b, 1., 1.0:8.0, si))]
     @test si == zeros(3) # Will likely fail if/when arrayviews are implemented
     si = [zeros(3) ones(3)]
-    @test filt(b, 1., [x 1.0:8.0], si) == [filt(b, 1., x, zeros(3)) filt(b, 1., 1.0:8.0, ones(3))]
+    @test first(filt(b, 1., [x 1.0:8.0], si)) == [first(filt(b, 1., x, zeros(3))) first(filt(b, 1., 1.0:8.0, ones(3)))]
     # With initial conditions: a lowpass 5-pole butterworth filter with W_n = 0.25,
     # and a stable initial filter condition matched to the initial value
     b = [0.003279216306360201,0.016396081531801006,0.03279216306360201,0.03279216306360201,0.016396081531801006,0.003279216306360201]
     a = [1.0,-2.4744161749781606,2.8110063119115782,-1.703772240915465,0.5444326948885326,-0.07231566910295834]
     si = [0.9967207836936347,-1.4940914728163142,1.2841226760316475,-0.4524417279474106,0.07559488540931815]
-    @test filt(b, a, ones(10), si) ≈ ones(10) # Shouldn't affect DC offset
+    @test first(filt(b, a, ones(10), si)) ≈ ones(10) # Shouldn't affect DC offset
 
     @test_throws ArgumentError filt!([1, 2], [1], [1], [1])
 end
diff --git a/test/filt.jl b/test/filt.jl
index 48dd04e65..8132bd3b8 100644
--- a/test/filt.jl
+++ b/test/filt.jl
@@ -155,6 +155,40 @@ end
     @test matlab_filt ≈ x
 end
 
+@testset "blockwise filt for $T" for T in [PolynomialRatio, ZeroPoleGain, SecondOrderSections], extra_dims in [(), (2,), (2, 3)]
+    x = rand(1000, extra_dims...)
+    H = T(PolynomialRatio([0.1, 0.1], [1, 0.8]))
+    y_ref = filt(H, x)
+    if T == PolynomialRatio
+        state = DSP.Filters._zerosi(H, x)
+    else
+        state = DSP.Filters._zerosi(SecondOrderSections(H), x)
+    end
+    y_test = similar(x)
+    all_cols = map(_ -> :, extra_dims)
+    for i in 1:100:size(x,1)
+        y_test[i:i+99, all_cols...], state = filt(H, x[i:i+99, all_cols...], state)
+    end
+    @test y_ref ≈ y_test
+end
+
+@testset "blockwise filt! for $T" for T in [PolynomialRatio, ZeroPoleGain, SecondOrderSections], extra_dims in [(), (2,), (2, 3)]
+    x = rand(1000, extra_dims...)
+    H = T(PolynomialRatio([0.1, 0.1], [1, 0.8]))
+    y_ref = filt(H, x)
+    if T == PolynomialRatio
+        state = DSP.Filters._zerosi(H, x)
+    else
+        state = DSP.Filters._zerosi(SecondOrderSections(H), x)
+    end
+    y_test = similar(x)
+    all_cols = map(_ -> :, extra_dims)
+    for i in 1:100:size(x,1)
+        _, state = filt!(view(y_test, i:i+99, all_cols...), H, x[i:i+99, all_cols...], state)
+    end
+    @test y_ref ≈ y_test
+end
+
 #######################################
 #
 # Test 1d filtfilt against matlab results