From b95c4d2d5d0cce6cc266027b6661020e9e5a2256 Mon Sep 17 00:00:00 2001
From: MaranBr <maranbr@outlook.com>
Date: Mon, 29 Dec 2025 20:24:57 +0100
Subject: [PATCH] [audio_core] Fix broken biquad effect (#3225)

This fixes the broken biquad effect.

Thanks to Forrest Mark X for showing us where the problem was occurring in the code.

Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/3225
Reviewed-by: Maufeat <sahyno1996@gmail.com>
Reviewed-by: DraVee <dravee@eden-emu.dev>
Co-authored-by: MaranBr <maranbr@outlook.com>
Co-committed-by: MaranBr <maranbr@outlook.com>
---
 .../renderer/command/command_buffer.cpp       | 40 +++++++++----------
 .../renderer/command/command_generator.cpp    |  6 ++-
 2 files changed, 22 insertions(+), 24 deletions(-)

diff --git a/src/audio_core/renderer/command/command_buffer.cpp b/src/audio_core/renderer/command/command_buffer.cpp
index 804aba438d..66f78f26b4 100644
--- a/src/audio_core/renderer/command/command_buffer.cpp
+++ b/src/audio_core/renderer/command/command_buffer.cpp
@@ -272,35 +272,31 @@ void CommandBuffer::GenerateBiquadFilterCommand(const s32 node_id, EffectInfoBas
         effect_info.GetStateBuffer() + channel * sizeof(VoiceState::BiquadFilterState))};
 
     if (behavior->IsEffectInfoVersion2Supported()) {
-        const auto& p{
+        const auto& parameter{
             *reinterpret_cast<BiquadFilterInfo::ParameterVersion2*>(effect_info.GetParameter())};
 
-        if (!IsChannelCountValid(p.channel_count) || channel < 0 || channel >= p.channel_count) {
-            return;
-        }
-
-        cmd.input = buffer_offset + p.inputs[channel];
-        cmd.output = buffer_offset + p.outputs[channel];
+        if (parameter.state <= EffectInfoBase::ParameterState::Updated && IsChannelCountValid(parameter.channel_count) && channel >= 0 && channel < parameter.channel_count) {
+            cmd.input = buffer_offset + parameter.inputs[channel];
+            cmd.output = buffer_offset + parameter.outputs[channel];
 
-        // Convert float coefficients to Q2.14 fixed-point as expected by the legacy DSP path.
-        cmd.biquad.b[0] = ToQ14Clamped(p.b[0]);
-        cmd.biquad.b[1] = ToQ14Clamped(p.b[1]);
-        cmd.biquad.b[2] = ToQ14Clamped(p.b[2]);
-        cmd.biquad.a[0] = ToQ14Clamped(p.a[0]);
-        cmd.biquad.a[1] = ToQ14Clamped(p.a[1]);
+            // Convert float coefficients to Q2.14 fixed-point as expected by the legacy DSP path.
+            cmd.biquad.b[0] = ToQ14Clamped(parameter.b[0]);
+            cmd.biquad.b[1] = ToQ14Clamped(parameter.b[1]);
+            cmd.biquad.b[2] = ToQ14Clamped(parameter.b[2]);
+            cmd.biquad.a[0] = ToQ14Clamped(parameter.a[0]);
+            cmd.biquad.a[1] = ToQ14Clamped(parameter.a[1]);
+        }
     } else {
-        const auto& p{
+        const auto& parameter{
             *reinterpret_cast<BiquadFilterInfo::ParameterVersion1*>(effect_info.GetParameter())};
 
-        if (!IsChannelCountValid(p.channel_count) || channel < 0 || channel >= p.channel_count) {
-            return;
-        }
-
-        cmd.input = buffer_offset + p.inputs[channel];
-        cmd.output = buffer_offset + p.outputs[channel];
+        if (IsChannelCountValid(parameter.channel_count) && channel >= 0 && channel < parameter.channel_count) {
+            cmd.input = buffer_offset + parameter.inputs[channel];
+            cmd.output = buffer_offset + parameter.outputs[channel];
 
-        cmd.biquad.b = p.b;
-        cmd.biquad.a = p.a;
+            cmd.biquad.b = parameter.b;
+            cmd.biquad.a = parameter.a;
+        }
     }
 
     // Effects always use the fixed-point coefficient path on the DSP.
diff --git a/src/audio_core/renderer/command/command_generator.cpp b/src/audio_core/renderer/command/command_generator.cpp
index bec6abbaf9..29d7c11d16 100644
--- a/src/audio_core/renderer/command/command_generator.cpp
+++ b/src/audio_core/renderer/command/command_generator.cpp
@@ -374,8 +374,10 @@ void CommandGenerator::GenerateBiquadFilterEffectCommand(const s16 buffer_offset
             LOG_ERROR(Service_Audio, "Biquad filter parameter is null");
             return;
         }
-        param_state = parameter->state;
-        channel_count = parameter->channel_count;
+        if (parameter->state <= EffectInfoBase::ParameterState::Updated) {
+            param_state = parameter->state;
+            channel_count = parameter->channel_count;
+        }
     } else {
         const auto* parameter =
             reinterpret_cast<const BiquadFilterInfo::ParameterVersion1*>(effect_info.GetParameter());