feat(VoiceRecorder): native 44.1kHz recording, band-pass filter, amp mute, 3x boost

- Keep 44.1kHz native sample rate to avoid linear resampler alias noise
- MIC_BOOST 300%% (3x) with clipping, after filtering per user request
- Low-pass 0.25 (~2.5kHz) to remove MCLK high-pitch hiss
- High-pass 0.985 (~100Hz) to remove DC/rumble/pop
- Chain: raw -> high-pass -> low-pass -> boost
- Disable FM8002E speaker amp GPIO1 during recording (active-low) to eliminate pop/hiss, re-enable after
- Add esp_driver_gpio requirement for gpio_set_level
- Previous UI improvements (date+duration list, green highlight, volume slider, full-screen layout) included in history

Apps/VoiceRecorder/main/Source/main.c

@@ -20,18 +20,22 @@
 #include "freertos/FreeRTOS.h"
 #include "freertos/task.h"
 #include "esp_log.h"
+#include "driver/gpio.h"
 
 #define TAG "VoiceRecorder"
 
-#define SAMPLE_RATE      16000
+#define SAMPLE_RATE      44100
 #define BITS_PER_SAMPLE  16
 #define CHUNK_SAMPLES    1024
 #define CHUNK_BYTES      (CHUNK_SAMPLES * (BITS_PER_SAMPLE / 8)) // 2048 bytes
 #define AUDIO_BUF_SIZE   8192
 
-// Software mic boost (digital gain) to compensate quiet MEMS mic even at 100% hw gain (24dB)
-// 200 = 2x, 300 = 3x – clipping protection via int16 limits
-#define MIC_BOOST_PERCENT 250
+// 3x boost + low-pass + high-pass (band-pass for voice)
+#define MIC_BOOST_PERCENT 300
+#define ENABLE_LOWPASS 1
+#define LOWPASS_ALPHA  0.25f   // ~2.5kHz cutoff, reduces high-pitch MCLK hiss
+#define ENABLE_HIGHPASS 1
+#define HIGHPASS_ALPHA 0.985f  // ~100Hz cutoff, removes DC/rumble/pop
 
 // ─── Scroll animation flags ───
 // LVGL label scroll animation (LV_LABEL_LONG_SCROLL_*) causes continuous
@@ -264,10 +268,15 @@ static void record_task(void* arg) {
 
     error_t err = audio_stream_open_input(ctx->stream_dev, &in_cfg, &ctx->input_handle);
     if (err == ERROR_NONE) {
-        // Ensure mic is unmuted and at max gain (ES8311 0..24dB)
+        // Disable speaker amp (GPIO1 active-low) to avoid FM8002E pop/hiss during recording
+        // Board es3c35p/es3c28p: amp_enable on GPIO1 low = enabled
+        gpio_set_level(GPIO_NUM_1, 1);
+        // Also mute output codec path
+        audio_stream_set_mute(ctx->stream_dev, AUDIO_CODEC_DIR_OUTPUT, true);
+        // Ensure mic is unmuted and at max gain (42dB HW max)
         audio_stream_set_mute(ctx->stream_dev, AUDIO_CODEC_DIR_INPUT, false);
         audio_stream_set_volume(ctx->stream_dev, AUDIO_CODEC_DIR_INPUT, 100.0f);
-        ESP_LOGI(TAG, "Mic unmuted, gain 100%%");
+        ESP_LOGI(TAG, "Amp disabled (GPIO1 HIGH), mic unmuted 42dB");
     }
     if (err != ERROR_NONE) {
         ESP_LOGE(TAG, "audio_stream_open_input failed: %d", err);
@@ -289,22 +298,45 @@ static void record_task(void* arg) {
     uint32_t start_time = xTaskGetTickCount();
     uint32_t last_ui_sec = 0;
     bool first_ui = true;
+#if ENABLE_LOWPASS
+    float lp_prev = 0.0f;
+#endif
+#if ENABLE_HIGHPASS
+    float hp_x_prev = 0.0f;
+    float hp_y_prev = 0.0f;
+#endif
 
     while (ctx->state == STATE_RECORDING) {
         size_t bytes_read = 0;
         err = audio_stream_read(ctx->input_handle, ctx->audio_buf, AUDIO_BUF_SIZE, &bytes_read, pdMS_TO_TICKS(200));
         if (err == ERROR_NONE && bytes_read > 0) {
-            // Software boost: 16-bit mono, apply MIC_BOOST_PERCENT with clipping
-#if MIC_BOOST_PERCENT != 100
             int16_t* samples = (int16_t*)ctx->audio_buf;
             size_t sample_cnt = bytes_read / sizeof(int16_t);
             for (size_t i = 0; i < sample_cnt; i++) {
-                int32_t boosted = (int32_t)samples[i] * MIC_BOOST_PERCENT / 100;
+                float in = (float)samples[i];
+#if ENABLE_HIGHPASS
+                // 1st-order high-pass ~100Hz to remove DC, rumble, pop
+                float hp_out = HIGHPASS_ALPHA * (hp_y_prev + in - hp_x_prev);
+                hp_x_prev = in;
+                hp_y_prev = hp_out;
+                in = hp_out;
+#endif
+#if ENABLE_LOWPASS
+                float lp_out = LOWPASS_ALPHA * in + (1.0f - LOWPASS_ALPHA) * lp_prev;
+                lp_prev = lp_out;
+                in = lp_out;
+#endif
+#if MIC_BOOST_PERCENT != 100
+                int32_t boosted = (int32_t)(in * MIC_BOOST_PERCENT / 100);
                 if (boosted > 32767) boosted = 32767;
                 if (boosted < -32768) boosted = -32768;
                 samples[i] = (int16_t)boosted;
-            }
+#else
+                if (in > 32767) in = 32767;
+                if (in < -32768) in = -32768;
+                samples[i] = (int16_t)in;
 #endif
+            }
             size_t written = fwrite(ctx->audio_buf, 1, bytes_read, f);
             if (written != bytes_read) {
                 ESP_LOGE(TAG, "SD write error: wrote %d of %d", (int)written, (int)bytes_read);
@@ -335,6 +367,10 @@ static void record_task(void* arg) {
 
     audio_stream_close(ctx->input_handle);
     ctx->input_handle = NULL;
+    // Re-enable speaker amp and unmute output after recording
+    audio_stream_set_mute(ctx->stream_dev, AUDIO_CODEC_DIR_OUTPUT, false);
+    gpio_set_level(GPIO_NUM_1, 0);
+    ESP_LOGI(TAG, "Recording done, amp re-enabled (GPIO1 LOW)");
 
     fseek(f, 0, SEEK_SET);
     write_wav_header(f, SAMPLE_RATE, BITS_PER_SAMPLE, 1, total_written);