example?

local falling = false

script.Parent.Humanoid.StateChanged:Connect(function(o,n)
    if n == Enum.HumanoidStateType.Freefall then
        falling = true
    elseif n == Enum.HumanoidStateType.Landed or n == Enum.HumanoidStateType.Running then
        falling = false
    end
    print(n)
end)

local function step()
    if not falling then
        local thing = script["step"..math.random(1,5)]:Clone()
        thing.Parent = script.Parent.HumanoidRootPart
        thing:Play()
        thing.TimePosition = 0
    end
end

while wait() do
    if script.Parent.HumanoidRootPart.Velocity.magnitude > 4 then
        wait(4/script.Parent.HumanoidRootPart.Velocity.magnitude)
        step()
    end
end