Audio effects implementation

1. Audio effects implementation ECE 3551 – Microcomputer Systems I By Md. Raqiq Islam

2. Overview • This project was created to use the Blackfin BF533 DSP to control audio output.Thefollowing features were included: • Audio effect Reverberation • Audio effect Chorus • Audio effect Echo • Volume control • Using SD RAM to store audio and play

3. Process data.c for the code • void reverberation_effect_volume_gain(void) • { • delay = temp - 400; // delay of 500 samples. If we increase the number of samples the reverberation effect tend towards the echo effect. • if(delay < 0) • { • delay = delay + 3000; // keeping the delay constant. If the value of temp is 0 then the delayed sample if 2500th sample in the array. • } • input1 = iChannel0LeftIn>>8; // bit shifting the input sample by 8 bits to make it compatible with short data type. • input2 = iChannel0RightIn>>8; // same as above • buffer_out1[temp] = input1 + 0.6*buffer_out1[delay]; // equation for the implementation of reverberation sound effect. • buffer_out2[temp] = input2 + 0.6*buffer_out2[delay]; // equation for the implementation of reverberation sound effect. • vol1 = buffer_out1[temp]<<16;

4. vol2 = buffer_out2[temp]<<16; • vol1_temp = vol1 + vol1*(.8)*(PF9_counter); // bit shifting the output 8 bits to the left to play 24 bit audio out. • vol2_temp = vol2 + vol2*(.8)*(PF9_counter); // bit shifting the output 8 bits to the left to play 24 bit audio out. • iChannel0LeftOut = vol1_temp>>8; • iChannel0RightOut = vol2_temp>>8; • temp++; • temp = temp%3000; // circular buffering to set the value of temp back to 0 if it exceeds 3000 or the array limit. • }

5. void SDRAM_store(void) • { • if(pSDRAM_var1 <= pSDRAM_end_address) • { • *pSDRAM_var1 = iChannel0LeftIn; // storing the input samples to the memory banks in SDRAM • *pSDRAM_var1 = iChannel0RightIn; • iChannel0LeftOut = iChannel0LeftIn; • iChannel0RightOut = iChannel0RightIn; • pSDRAM_var1++; // incrementing the position of memory bank by 1 place • } • }

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