ESP32 Forum

Posted: **Mon Oct 21, 2024 5:45 pm**

Hi. I'm currently developing code using ESP-ADF, where I created a custom audio element to process the samples of the right channel in order to implement a feedback process in some kind of passthru program. However, I don't know how to properly understand the samples since I expected that whenever I had silence detected from the microphone, the samples should be around the value of 32768 (which is half the maximum value). Instead, I am getting samples around the maximum and minimum values:

I (58355) PASSTHRU: RSample: 65146
I (58365) PASSTHRU: RSample: 64844
I (58385) PASSTHRU: RSample: 64878
I (58415) PASSTHRU: RSample: 85
I (58445) PASSTHRU: RSample: 765
I (58475) PASSTHRU: RSample: 867
I (58485) PASSTHRU: RSample: 204
I (58505) PASSTHRU: RSample: 64932
I (58535) PASSTHRU: RSample: 64773
I (58565) PASSTHRU: RSample: 286
I (58595) PASSTHRU: RSample: 131
I (58605) PASSTHRU: RSample: 651
I (58625) PASSTHRU: RSample: 184
I (58655) PASSTHRU: RSample: 398
I (58685) PASSTHRU: RSample: 64980

Additionally, it all sounds good when I plug the output into a speaker, so I know it's purely an interpretation issue.
I hope some of you can help me understand how these samples truly work so I can continue developing my program.

This is the code I'm currently using:

Code: [Select all] [Expand/Collapse]

ESP_LOGI(TAG, "[ 2 ] Start codec chip");
    audio_board_handle_t board_handle = audio_board_init();
    audio_hal_ctrl_codec(board_handle->audio_hal, AUDIO_HAL_CODEC_MODE_BOTH, AUDIO_HAL_CTRL_START);
    audio_hal_set_volume(board_handle->audio_hal, 60); //60
 
    ESP_LOGI(TAG, "[ 2 ] Create audio pipeline for playback");
    audio_pipeline_cfg_t pipeline_cfg = DEFAULT_AUDIO_PIPELINE_CONFIG();
    pipeline = audio_pipeline_init(&pipeline_cfg);
 
    ESP_LOGI(TAG, "[ 3 ] Create i2s stream to write data to codec chip");
    i2s_stream_cfg_t i2s_cfg_w = I2S_STREAM_CFG_DEFAULT();
    i2s_cfg_w.type = AUDIO_STREAM_WRITER;
    i2s_stream_set_channel_type(&i2s_cfg_w,I2S_CHANNEL_TYPE_ALL_LEFT);
    i2s_stream_writer = i2s_stream_init(&i2s_cfg_w);
 
    ESP_LOGI(TAG, "[ 3.1 ] Create i2s stream to read data from codec chip");
    i2s_stream_cfg_t i2s_cfg_r = I2S_STREAM_CFG_DEFAULT();
    i2s_cfg_r.type = AUDIO_STREAM_READER;
    i2s_stream_set_channel_type(&i2s_cfg_r,I2S_CHANNEL_TYPE_ALL_LEFT);
    i2s_stream_reader = i2s_stream_init(&i2s_cfg_r);

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Code: [Select all] [Expand/Collapse]

static int audio_inverter_process(audio_element_handle_t self, char* buf, int len)
{
    int rsize = audio_element_input(self, buf, len);
 
    if (len != rsize || (rsize % 4) != 0) {
        ESP_LOGW(TAG, "unexpected rsize: %d, len: %d", rsize, len);
    }
 
    uint16_t LSample;
    char * lsamplep = (char *) &LSample;
    uint16_t RSample;
    char * rsamplep = (char *) &RSample;
    float sample = 0;
 
    for (int i =0; i<rsize; i+=4) {
        rsamplep[0] = buf[i];
        rsamplep[1] = buf[i+1];
        lsamplep[0] = buf[i+2];
        lsamplep[1] = buf[i+3];
        
        buf[i] = rsamplep[0];
        buf[i+1] = rsamplep[1];
        buf[i+2] = lsamplep[0];
        buf[i+3] = lsamplep[1];
    }
 
    ESP_LOGI(TAG, "RSample: %hu",RSample);
    
    rsize = audio_element_output(self, buf, rsize);
 
    return rsize;
}

Posted: **Tue Oct 22, 2024 8:20 am**

CoolingCoder wrote: ↑
Mon Oct 21, 2024 5:45 pm
so I know it's purely an interpretation issue.
I hope some of you can help me understand how these samples truly work

Interpret the samples as signed values, i.e. int16_t.

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