How to create echo delay in audio

Altera_Forum · ‎12-03-2008

Hello, im working on a project that needs to reproduce an audio signal using the the DE2 board. I need to create several effect for the final output, and one of them is the delay of the input signal causing echo. I im basing my project on the DE2_i2csound example.

The signal im working on is called RIGHTDATA and LEFTDATA, they already

have the volume adjusted.

The problem is that i dont get any echo after the sum of the original signal and the delay one.

I dont know if that is the right place to save the delayed signals.

Thankyou for your time...

MAQUINA: PROCESS (CLK,LR,BCLK,COUNTER_L,COUNTER_R)

BEGIN

if (rising_edge(CLK)) then

CC1<=CC0;

CC0<=BCLK;

if ((C1='0') and (C0='1')) then

if (LR='0') then

case (COUNTER_R) IS

when 0=> RIN(15)<=ADC;

DAC<=ROUT(15);

when 1=> RIN(14)<=ADC;

DAC<=ROUT(14);

when 2=> RIN(13)<=ADC;

DAC<=ROUT(13);

when 3=> RIN(12)<=ADC;

DAC<=ROUT(12);

when 4=> RIN(11)<=ADC;

DAC<=ROUT(11);

when 5=> RIN(10)<=ADC;

DAC<=ROUT(10);

when 6=> RIN(9)<=ADC;

DAC<=ROUT(9);

when 7=> RIN(8)<=ADC;

DAC<=ROUT(8);

when 8=> RIN(7)<=ADC;

DAC<=ROUT(7);

when 9 => RIN(6)<=ADC;

DAC<=ROUT(6);

when 10=> RIN(5)<=ADC;

DAC<=ROUT(5);

when 11=> RIN(4)<=ADC;

DAC<=ROUT(4);

when 12=> RIN(3)<=ADC;

DAC<=ROUT(3);

when 13=> RIN(2)<=ADC;

DAC<=ROUT(2);

when 14=> RIN(1)<=ADC;

DAC<=ROUT(1);

when 15=> RIN(0)<=ADC;

DAC<=ROUT(0);

when 16=>

if (MUTE='1') then

--ROUT<=RIN;

ROUT(15 downto 0)<=RAM_R(9)+RIGHTDATA(19 DOWNTO 4);

RAM_R(9)<=RAM_R(8);

RAM_R(8)<=RAM_R(7);

RAM_R(7)<=RAM_R(6);

RAM_R(6)<=RAM_R(5);

RAM_R(5)<=RAM_R(4);

RAM_R(4)<=RAM_R(3);

RAM_R(3)<=RAM_R(2);

RAM_R(2)<=RAM_R(1);

RAM_R(1)<=RAM_R(0);

RAM_R(0)<=RIGHTDATA(19 DOWNTO 4);

else

ROUT<= (others=>'0');

end if;

when others=>

DAC<='0';

end case;

else

case (COUNTER_L) IS

when 0=> LIN(15)<=ADC;

DAC<=LOUT(15);

when 1=> LIN(14)<=ADC;

DAC<=LOUT(14);

when 2=> LIN(13)<=ADC;

DAC<=LOUT(13);

when 3=> LIN(12)<=ADC;

DAC<=LOUT(12);

when 4=> LIN(11)<=ADC;

DAC<=LOUT(11);

when 5=> LIN(10)<=ADC;

DAC<=LOUT(10);

when 6=> LIN(9)<=ADC;

DAC<=LOUT(9);

when 7=> LIN(8)<=ADC;

DAC<=LOUT(8);

when 8=> LIN(7)<=ADC;

DAC<=LOUT(7);

when 9=> LIN(6)<=ADC;

DAC<=LOUT(6);

when 10=> LIN(5)<=ADC;

DAC<=LOUT(5);

when 11=> LIN(4)<=ADC;

DAC<=LOUT(4);

when 12=> LIN(3)<=ADC;

DAC<=LOUT(3);

when 13=> LIN(2)<=ADC;

DAC<=LOUT(2);

when 14=> LIN(1)<=ADC;

DAC<=LOUT(1);

when 15=> LIN(0)<=ADC;

DAC<=LOUT(0);

when 16=>

if (MUTE='1') then

LOUT(15 downto 0)<=RAM_L(9)+LEFTDATA(19 DOWNTO 4);

RAM_L(9)<=RAM_L(8);

RAM_L(8)<=RAM_L(7);

RAM_L(7)<=RAM_L(6);

RAM_L(6)<=RAM_L(5);

RAM_L(5)<=RAM_L(4);

RAM_L(4)<=RAM_L(3);

RAM_L(3)<=RAM_L(2);

RAM_L(2)<=RAM_L(1);

RAM_L(1)<=RAM_L(0);

RAM_L(0)<=LEFTDATA(19 DOWNTO 4);

else

LOUT<= (others=>'0');

end if;

when others=>

DAC<='0';

end case;

end if;

END PROCESS MAQUINA;

Altera_Forum · ‎12-03-2008

If I understood well, in your code, things happend too quick to get an echo effect.

Regards.

Alberto.

Altera_Forum · ‎12-03-2008

As a first remark, without signal and type definition, your code isn't understandable. I'm not motivated to guess about possible data definitions. Also the ADC and DAC data processing isn't clear, but it's not directly related to your question. I simply assume, that you are able to interface the audio codec correctly.

Echo usually implies a delay above 100 ms, respectively a few thousand samples, but may range up to many seconds. This can be done with RAM ring buffer, addressed by write and read pointers. The read pointer offset defines the delay. However, FPGA internal RAM is only sufficient for very small delays, external RAM would be better suited.