filter implementierung

[Serge D. (lafesse)]

Hallo,
ich bin ein vhdl anfäger und habe folgende code um ein digitales filter 
zu implementieren.nun zeigt er zwar keine fehler an bei compilieren aber 
wenn ich die koefficiennten tausche...versteht es jemand...bzw kann mir 
bitte jemand erklären ob man die berechnete coefficienten umrechnen 
musst?und wie?
danke im vorraus

library IEEE;
use IEEE.std_logic_1164.all;
use IEEE.numeric_std.all;

entity filter is
--generic ( FILTERLAENGE :natural:=6;
      -- FILTERKOEFF :array (natural range 0 to FILTERLAENGE - 1) of 
signed( 7 downto 0) :=(-1,-1,-1,-1,-1,-1)
      -- );
port (
    clk           : IN  STD_LOGIC;
    reset         : IN  STD_LOGIC;
    filterGO      : IN  STD_LOGIC;
    filterEingang : IN  STD_LOGIC_VECTOR (15 downto 0);
    filterAusgang : OUT STD_LOGIC_VECTOR (15 downto 0)
  );
end;

architecture beh of filter is

constant FILTERLAENGE: natural := 6;
type t_memory is array (natural range 0 to FILTERLAENGE - 1) of 
signed(15 downto 0);
type t_Koeff  is array (natural range 0 to FILTERLAENGE - 1) of signed( 
7 downto 0);

constant FILTERKOEFF: t_Koeff := (to_signed(1, 8), to_signed(1, 8), 
to_signed(1, 8),
                  to_signed(1, 8), to_signed(1, 8), to_signed(1, 8));
signal Speicher: t_memory;

begin

  process(clk, reset)
    variable filterMult:  signed(23 downto 0) := (others => '0');
    variable filterSumme: signed(24 downto 0) := (others => '0');
  begin
    if (reset = '0') then
      filterAusgang <= (others => '0');
      Speicher      <= (others => (others => '0'));
    elsif (rising_edge(clk)) then
      if (filterGO = '1') then
        -- held samples from "filterEingang" stored in Speicher
        for I in 0 to FILTERLAENGE - 2
        loop
          Speicher(I) <= Speicher(I + 1);
        end loop;
        Speicher(FILTERLAENGE - 1) <= signed(filterEingang);

        -- filter operation y(n) = b0*x(n) + b1*x(n - 1) + ... + bn*x(0)
        filterSumme := (others => '0');
        for I in 0 to FILTERLAENGE - 1
        loop
          filterMult := FILTERKOEFF(I)*Speicher(FILTERLAENGE - (I + 1));
          filterSumme:= filterSumme + resize(filterMult, 25);
        end loop;

        -- current filter result in "filterSumme" has 25 bits width
        -- needed y(n) has to be a 16 bits data
        filterAusgang <= std_logic_vector(resize(filterSumme, 16));
      end if;
    end if;
  end process;

end beh;