Fix band-0 DC filter to downmix configs 3/4

include/eac3joc_core.h

@@ -64,6 +64,15 @@ EJOC_API ejoc_renderer_handle EJOC_CALL ejoc_renderer_create(void);
 EJOC_API void EJOC_CALL ejoc_renderer_destroy(ejoc_renderer_handle handle);
 EJOC_API int EJOC_CALL ejoc_renderer_reset(ejoc_renderer_handle handle);
 EJOC_API int EJOC_CALL ejoc_renderer_set_threads(ejoc_renderer_handle handle, uint32_t total_threads);
+/*
+Enables or disables the Ls/Rs band-0 21-tap DC compensation. The caller derives
+it from the JOC downmix configuration: only configurations 3 and 4 enable the
+filter. When disabled, band 0 keeps the common per-band processing (surround
+delay plus -j rotation) instead of being overwritten by the FIR. The delay line
+and DC history advance either way, so the flag may change between frames.
+Defaults to enabled when never called.
+*/
+EJOC_API int EJOC_CALL ejoc_renderer_set_dc_filter(ejoc_renderer_handle handle, uint32_t enabled);
 EJOC_API uint32_t EJOC_CALL ejoc_renderer_thread_count(ejoc_renderer_handle handle);
 EJOC_API const char* EJOC_CALL ejoc_renderer_last_error(ejoc_renderer_handle handle);
 

src/joc_core/eac3joc_core.cpp

@@ -125,6 +125,10 @@ public:
         return error_[0] ? error_ : "";
     }
 
+    void set_dc_filter(const bool enabled) noexcept {
+        dc_filter_enabled_ = enabled;
+    }
+
     int process(
         const float* bed5,
         const float* lfe,
@@ -305,16 +309,18 @@ private:
                 for (int i = 0; i < 4; ++i) {
                     dc_buffer[20 + i] = current[i][0];
                 }
-                for (int slot = 0; slot < 4; ++slot) {
-                    Complex sum{0.0, 0.0};
-                    for (int tap = 0; tap < 21; ++tap) {
-                        const Complex sample = dc_buffer[slot + tap];
-                        const double cr = kDcB[tap];
-                        const double ci = kDcA[tap];
-                        sum.re += sample.re * cr - sample.im * ci;
-                        sum.im += sample.re * ci + sample.im * cr;
+                if (dc_filter_enabled_) {
+                    for (int slot = 0; slot < 4; ++slot) {
+                        Complex sum{0.0, 0.0};
+                        for (int tap = 0; tap < 21; ++tap) {
+                            const Complex sample = dc_buffer[slot + tap];
+                            const double cr = kDcB[tap];
+                            const double ci = kDcA[tap];
+                            sum.re += sample.re * cr - sample.im * ci;
+                            sum.im += sample.re * ci + sample.im * cr;
+                        }
+                        x_[channel][0][group + slot] = {2.0 * sum.re, 2.0 * sum.im};
                     }
-                    x_[channel][0][group + slot] = {2.0 * sum.re, 2.0 * sum.im};
                 }
                 for (int i = 0; i < 20; ++i) {
                     surround_history_[surround][i] = dc_buffer[i + 4];
@@ -641,6 +647,8 @@ private:
     float analysis_phase_;
     alignas(64) Complex surround_delay_[2][10][64];
     alignas(64) Complex surround_history_[2][20];
+    // band-0 的 21-tap DC 补偿开关；仅 downmix 配置 3/4 由调用方置位。
+    bool dc_filter_enabled_ = true;
     alignas(64) double lfe_delay_[kLfeDelay];
     alignas(64) double matrix_previous_[15][5][64];
     alignas(64) double synthesis_state_[15][640];
@@ -696,6 +704,14 @@ int EJOC_CALL ejoc_renderer_set_threads(ejoc_renderer_handle handle, uint32_t to
     return static_cast<ejoc::Renderer*>(handle)->set_threads(total_threads);
 }
 
+int EJOC_CALL ejoc_renderer_set_dc_filter(ejoc_renderer_handle handle, uint32_t enabled) {
+    if (!handle) {
+        return -1;
+    }
+    static_cast<ejoc::Renderer*>(handle)->set_dc_filter(enabled != 0);
+    return 0;
+}
+
 uint32_t EJOC_CALL ejoc_renderer_thread_count(ejoc_renderer_handle handle) {
     if (!handle) {
         return 0;

src/joc_core/objects16.cpp

@@ -52,6 +52,15 @@ Status rebuild_objects16(ejoc_renderer_handle handle, const joc_frame_params& pa
     }
 
     out16->assign(static_cast<std::size_t>(JOC_OUTPUT_CHANNELS) * JOC_FRAME_SAMPLES, 0.0f);
+    // band-0 的 21-tap DC 补偿只在 downmix 配置 3/4 下启用，其余配置 band 0
+    // 走与其他 band 相同的处理。
+    const bool dc_filter = params.dmx_config_idx == 3 || params.dmx_config_idx == 4;
+    if (ejoc_renderer_set_dc_filter(handle, dc_filter ? 1u : 0u) != 0) {
+        if (error != nullptr) {
+            *error = "ejoc_renderer_set_dc_filter failed";
+        }
+        return Status::fail(JOC_ERR_RENDER_FAILED, stage::kDsp, "ejoc_renderer_set_dc_filter failed");
+    }
     const int result = ejoc_renderer_process(
         handle, bed5_planar, lfe, params.present_mask, n_bands, n_dpoints, slope_idx, offset_ts,
         dq.data(), params.clipgain, 0.0625f, gain, out16->data());