diff --git a/README.md b/README.md
index 0b8c069..527aa5b 100644
--- a/README.md
+++ b/README.md
@@ -83,4 +83,5 @@ README.md
 
 | 日期 | 说明 |
 |------|------|
+| 2026-10-27 | 修复无声贝变化：I2S 改立体声读槽（ESP32 L/R 与麦脚常反相）+ 去直流后再算 RMS |
 | 2026-10-27 | 初版：INMP441 I2S 声贝仪表盘（WS22/SCK27/SD35），LVGL 圆弧 + peak/min/max + 趋势图 |
diff --git a/firmware/cyd_28r/VERSION.txt b/firmware/cyd_28r/VERSION.txt
index 4d1fccf..dced4f4 100644
--- a/firmware/cyd_28r/VERSION.txt
+++ b/firmware/cyd_28r/VERSION.txt
@@ -1,5 +1,5 @@
 name: CYD inmp441test (cyd_28r)
-git: unknown
+git: 59b85fb
 date: 2026-10-27
 board: ESP32-2432S028R (ILI9341)
 inmp441: WS=GPIO22 SCK=GPIO27 SD=GPIO35
@@ -13,5 +13,5 @@ offsets:
 sha256:
   bootloader.bin  3D234A7471F67B013686DABD4DEE7C1FA915C9928463616A94BC9297ACF1ABF8
   boot_app0.bin   F94C5D786A7A8FAB06AC5D10E33BF37711A6697636DC037559EA19CC410A17F0
-  firmware.bin    0CA34A45377F5EDCAB501E510F97B28A9B7FCEB34D6C65F0B71691C784C41999
+  firmware.bin    81B26992192E72F77396E0B71782C145EFE106F996D9E432F1551F5182CC6710
   partitions.bin  0A8B5720E7B77FF11F1462458C3A509DEE79224E5279898F26D6A2E3AE0517B7
diff --git a/firmware/cyd_28r/firmware.bin b/firmware/cyd_28r/firmware.bin
index 46ef4fa..bb46c42 100644
Binary files a/firmware/cyd_28r/firmware.bin and b/firmware/cyd_28r/firmware.bin differ
diff --git a/src/main.cpp b/src/main.cpp
index 7ea3543..f573ba7 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -3,7 +3,8 @@
  * 2.8 (2432S028R): WS=22 SCK=27 SD=35, TFT_BL=21
  * 3.5C (3248S035C): WS=22 SCK=21 SD=35, TFT_BL=27 — see ../CYD_PROJECT_GUIDE.md
  *
- * L/R -> GND（左声道）；VDD -> 3.3V（勿接 5V）
+ * L/R -> GND（推荐）；VDD -> 3.3V（勿接 5V）
+ * ESP32 I2S 声道命名常与 INMP441 反相：L/R=GND 时用 RIGHT 槽才有数据。
  */
 
 #include <Arduino.h>
@@ -17,7 +18,7 @@
 #define I2S_PORT I2S_NUM_0
 #define SAMPLE_RATE 16000
 #define SAMPLE_BITS 32
-#define DMA_BUF_COUNT 4
+#define DMA_BUF_COUNT 8
 #define DMA_BUF_LEN 256
 #define READ_SAMPLES 512
 #define MIC_READ_MS 80
@@ -223,7 +224,9 @@ static bool mic_init(void) {
   cfg.mode = (i2s_mode_t)(I2S_MODE_MASTER | I2S_MODE_RX);
   cfg.sample_rate = SAMPLE_RATE;
   cfg.bits_per_sample = I2S_BITS_PER_SAMPLE_32BIT;
-  cfg.channel_format = I2S_CHANNEL_FMT_ONLY_LEFT;
+  /* Stereo: ESP32 left/right vs INMP441 L/R pin are often inverted.
+   * L/R=GND usually lands in the RIGHT DMA slot on classic ESP32. */
+  cfg.channel_format = I2S_CHANNEL_FMT_RIGHT_LEFT;
   cfg.communication_format = I2S_COMM_FORMAT_STAND_I2S;
   cfg.intr_alloc_flags = ESP_INTR_FLAG_LEVEL1;
   cfg.dma_buf_count = DMA_BUF_COUNT;
@@ -247,31 +250,79 @@ static bool mic_init(void) {
     return false;
   }
   i2s_zero_dma_buffer(I2S_PORT);
+  Serial.printf("I2S stereo RX  WS=%d SCK=%d SD=%d\n",
+                I2S_WS_PIN, I2S_SCK_PIN, I2S_SD_PIN);
   return true;
 }
 
 static bool mic_read_db(float *out_db, float *out_rms) {
   size_t bytes_read = 0;
   esp_err_t err = i2s_read(I2S_PORT, (void *)i2s_samples, sizeof(i2s_samples),
-                           &bytes_read, pdMS_TO_TICKS(40));
+                           &bytes_read, pdMS_TO_TICKS(50));
   if (err != ESP_OK || bytes_read < sizeof(int32_t) * 32) {
     return false;
   }
 
   int n = (int)(bytes_read / sizeof(int32_t));
-  double sum_sq = 0.0;
-  int used = 0;
-  for (int i = 0; i < n; i++) {
-    /* INMP441: 24-bit left-justified in 32-bit word */
-    int32_t s = i2s_samples[i] >> 8;
-    sum_sq += (double)s * (double)s;
-    used++;
-  }
-  if (used < 16) return false;
+  if (n < 32) return false;
+
+  /* Unpack 24-bit left-justified samples; stereo slots alternate. */
+  static int32_t unpacked[READ_SAMPLES];
+  for (int i = 0; i < n; i++) {
+    unpacked[i] = i2s_samples[i] >> 8;
+  }
+
+  /* Measure even/odd slots separately (ESP32 L/R naming vs mic L/R pin). */
+  double mean_even = 0.0, mean_odd = 0.0;
+  int n_even = 0, n_odd = 0;
+  for (int i = 0; i < n; i++) {
+    if ((i & 1) == 0) {
+      mean_even += unpacked[i];
+      n_even++;
+    } else {
+      mean_odd += unpacked[i];
+      n_odd++;
+    }
+  }
+  if (n_even < 8 || n_odd < 8) return false;
+  mean_even /= (double)n_even;
+  mean_odd /= (double)n_odd;
+
+  double sum_even = 0.0, sum_odd = 0.0;
+  int32_t peak_abs = 0;
+  for (int i = 0; i < n; i++) {
+    double v;
+    if ((i & 1) == 0) {
+      v = (double)unpacked[i] - mean_even;
+      sum_even += v * v;
+    } else {
+      v = (double)unpacked[i] - mean_odd;
+      sum_odd += v * v;
+    }
+    int32_t a = (int32_t)((v < 0) ? -v : v);
+    if (a > peak_abs) peak_abs = a;
+  }
+
+  double rms_even = sqrt(sum_even / (double)n_even);
+  double rms_odd = sqrt(sum_odd / (double)n_odd);
+  double rms = (rms_even > rms_odd) ? rms_even : rms_odd;
+  const char *slot = (rms_even >= rms_odd) ? "L/even" : "R/odd";
+
+  static uint8_t dbg = 0;
+  if (dbg < 10) {
+    dbg++;
+    Serial.printf(
+        "raw=%08lX/%08lX meanE=%.0f meanO=%.0f rmsE=%.0f rmsO=%.0f peak=%ld %s\n",
+        (unsigned long)(uint32_t)i2s_samples[0],
+        (unsigned long)(uint32_t)i2s_samples[1], mean_even, mean_odd, rms_even,
+        rms_odd, (long)peak_abs, slot);
+  }
 
-  double rms = sqrt(sum_sq / (double)used);
   *out_rms = (float)rms;
-  if (rms < 1.0) rms = 1.0;
+  if (rms < 1.0) {
+    *out_db = 0.0f;
+    return true;
+  }
   /* dBFS vs 24-bit full scale, then map to approximate SPL */
   float dbfs = 20.0f * log10f((float)rms / 8388607.0f);
   *out_db = dbfs + MIC_DB_OFFSET;