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Altera_Forum
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16 years ago

Pre-Emphasis with IIR Filter

Hello! I want to do a classic Pre-Emphasis with VHDL. Normally this is implemented with an IIR-Filter. I tried to do this in VHDL with the following formula I found in the web: y(i)=x(i)-(x(i-1...
Altera_Forum's avatar
Altera_Forum
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16 years ago

I tried this code and I think the pre-emphasis works. But the output-signal is very distorted in the higher frequencies and the lower frequencies are very attenuated. Here is the modified VHDL-code:

if (rst = '0') then

xi := (others => '0');

xi1 := (others => '0');

yn_tmp := (others => '0');

yn_tmp2 := (others => '0');

b0_var := ("01100001"); --97

div := ("01100100"); --100

elsif (clk'event and clk = '1') then

x <= input;

xi := x; --new value

yn_tmp := xi1 * b0_var;

yn_tmp2 := yn_tmp / div;

yn := resize(xi, yn_tmp2'length) - yn_tmp2;

output <= resize(yn, output'length);

xi1 := xi; --old value

end if;

Normally the lower frequencies would go through without gain and the higher frequencies starting at 3 kHz have to be boosted with 6dB/octave.