diff --git a/Project.toml b/Project.toml
index 918b304..c1eb5d3 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,12 +1,13 @@
 name = "RoomAcoustics"
 uuid = "9b22aa7e-b0d0-4fe8-9c3b-2b8bf774f735"
 authors = ["Szymon M. Woźniak <s@zymon.org>"]
-version = "0.3.0"
+version = "0.3.1"
 
 [deps]
 DSP = "717857b8-e6f2-59f4-9121-6e50c889abd2"
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
 Random = "9a3f8284-a2c9-5f02-9a11-845980a1fd5c"
+SLEEFPirates = "476501e8-09a2-5ece-8869-fb82de89a1fa"
 StaticArrays = "90137ffa-7385-5640-81b9-e52037218182"
 Statistics = "10745b16-79ce-11e8-11f9-7d13ad32a3b2"
 
diff --git a/src/ISM.jl b/src/ISM.jl
index 079d006..0d0d921 100644
--- a/src/ISM.jl
+++ b/src/ISM.jl
@@ -145,6 +145,11 @@ function ISM_RectangularRoom_core!(
     # Transform size of the room from meters to samples
     Lₛ = L ./ Γ
 
+    # Impulse parameters
+    Δt = 1 / fs
+    ω = 2π / Wd
+    twid = π * fs
+
     # Compute maximal wall reflection
     N = ceil.(Int, Nh ./ (2 .* Lₛ))
 
@@ -216,10 +221,11 @@ function ISM_RectangularRoom_core!(
 
                     # Insert yet another impulse into transfer function
                     for i ∈ i_s:i_e
-                        t = (i - 1) / fs - τ # time signature
-                        w = 0.5 * (1.0 + cos(2π * t / Wd)) # Hann window
-                        x = π * fs * t + eps()
-                        h[i] += w * A * sin(x)/x
+                        t = (i - 1) * Δt - τ # time signature
+                        w = fma(cos_fast(ω*t), 0.5, 0.5) # Hann window
+                        x = twid * t
+                        sinc = ifelse(iszero(x), 1.0,  sin_fast(x)/x)
+                        @inbounds h[i] +=  w * A * sinc
                     end
                 end
             end
diff --git a/src/RoomAcoustics.jl b/src/RoomAcoustics.jl
index 04f8d9c..f37abfe 100644
--- a/src/RoomAcoustics.jl
+++ b/src/RoomAcoustics.jl
@@ -6,6 +6,7 @@ using Statistics
 using Random
 using Random: GLOBAL_RNG
 
+using SLEEFPirates: cos_fast, sin_fast
 using DSP: conv
 
 include("TxRxModels.jl")