Wiki

This version (28 Feb 2019 18:06) was approved by Chad Wentworth.The Previously approved version (13 Dec 2018 19:43) is available.

Tutorial: Chaining Audio Elements and Audio Effects

The power of the audio elements is how they can be combined in novel ways to create audio effects. In this tutorial, we'll implement a bank of band-pass filters that feed into a set of different delay lines set to different delay lengths.

To do this, we'll first need to declare instances of the biquad and integer_delay_lpf audio elements at the top of src/callback_audio_processing.cpp on the first SHARC core.

// Declarations for struct/instances for filters 
BIQUAD_FILTER filt_300Hz, filt_900Hz;
float pm filt_300Hz_coeffs[4]; 
float pm filt_900Hz_coeffs[4];
 
// Declaration of delay element structs and buffers for delay lines
DELAY_LPF     delay_1, delay_2;
float    section("seg_sdram") delay_buffer_1[AUDIO_SAMPLE_RATE*2];
float    section("seg_sdram") delay_buffer_2[AUDIO_SAMPLE_RATE*2];

Next, we'll set up the instances in the processaudio_setup() function in src/callback_audio_processing.cpp on the first SHARC core.

void processaudio_setup(void) {
 
    // *******************************************************************************
    // Add any custom setup code here
    // *******************************************************************************
 
    // Set up filters
    filter_setup(&filt_300Hz,
                 BIQUAD_TYPE_BPF,
                 BIQUAD_TRANS_MED,
                 filt_300Hz_coeffs,
                 300.0,  // Center frequency
                 4.0,    // Q
                 1.0,    // Gain (db)
                 AUDIO_SAMPLE_RATE);
    filter_setup(&filt_900Hz,
                 BIQUAD_TYPE_BPF,
                 BIQUAD_TRANS_MED,
                 filt_900Hz_coeffs,
                 900.0,  // Center frequency
                 4.0,    // Q
                 1.0,    // Gain (db)
                 AUDIO_SAMPLE_RATE);   
 
    // Set up delay lines
    delay_setup(&delay_1,
                delay_buffer_1,
                AUDIO_SAMPLE_RATE*2,
                AUDIO_SAMPLE_RATE*0.25, // set delay line initially to 0.25 seconds
                0.8,  // Feedthrough
                0.6,  // Feedback
                0.0); // Dampening coefficient (0=no dampening)
 
    delay_setup(&delay_2,
                delay_buffer_2,
                AUDIO_SAMPLE_RATE*2,
                AUDIO_SAMPLE_RATE*0.5, // set delay line initially to 0.5 seconds
                0.8,  // Feedthrough
                0.6,  // Feedback
                0.0); // Dampening coefficient (0=no dampening)               
 
}

Finally, we'll process audio in void processaudio_callback(void). First, we will run the biquads on the incoming left and right audio channels and save the outputs to a pair of buffers called 'audio_temp_1' and 'audio_temp_2'. We'll then use these buffers as the inputs to our delay functions. Finally, we'll send the outputs of the delay function to the left channel and right channel outputs.

void processaudio_callback(void) {
 
    float audio_temp_1[AUDIO_BLOCK_SIZE];
    float audio_temp_2[AUDIO_BLOCK_SIZE];
 
    // Run filters on incoming L/R input audio
    filter_read(&filt_300Hz, audiochannel_0_left_in, audio_temp_1, AUDIO_BLOCK_SIZE);
    filter_read(&filt_900Hz, audiochannel_0_right_in, audio_temp_2, AUDIO_BLOCK_SIZE);
 
    // Run filtered audio through delay lines and send to L/R/ output audio
    delay_read(&delay_1, audio_temp_1, audiochannel_0_left_out, AUDIO_BLOCK_SIZE);
    delay_read(&delay_2, audio_temp_2, audiochannel_0_right_out, AUDIO_BLOCK_SIZE);
 
}

Prev.: Programming a Volume ControlUp: Bare Metal FrameworkNext.: Building a 2.1 Amplifier

Analog Devices Wiki

Tutorial: Chaining Audio Elements and Audio Effects

Page Tools