Comparison with Other Platforms

Oct 13, 2025 by wbrum.org 105 views

Introduction

In this article, we will discuss a spatial panning problem found in Godot's AudioStreamPlayer3D class. The issue is related to the incorrect implementation of stereo panning, which results in a distorted audio experience. We will explore the problem, analyze the issue, and propose a solution based on industry-standard practices.

Tested Versions

The problem has been reproduced in Godot version 4.4.

System Information

The system information is as follows:

Godot version: 4.4.stable (77dcf97d8)
Operating System: NixOS
Display Driver: X11
OpenGL Version: 3 (Compatibility)
Graphics Card: Intel(R) Graphics (ADL GT2)
Processor: 12th Gen Intel(R) Core(TM) i5-1240P (16 threads)

Issue Description

The purpose of this issue is to draw together the observations of a bug found in the Godot engine and argue about what the solution is. The bug is related to the incorrect implementation of stereo panning in the AudioStreamPlayer3D class. The issue is that the panning strength is not being applied correctly, resulting in a distorted audio experience.

Observations

To understand the issue, we need to analyze the problem. We can do this by plotting the amplitude of the AudioEffectCaptured left and right channels on a polar graph. The resulting graph shows that the panning strength is not being applied correctly, resulting in a distorted audio experience.

Panning Strength = 1	Panning Strength = 0.3

Comparison with Other Platforms

To understand the issue better, we need to compare the Godot engine's implementation with other platforms. We can do this by analyzing the implementation of stereo panning in Unreal Engine, Unity, and Web Audio.

Unreal Engine

In Unreal Engine, the azimuth angle is computed, and then the function FMixerDevice::Get3DChannelMap() in AudioMixerDevice.cpp finds which two speakers it lies between, interpolates its angle position between them as the value Fraction, and sets their panning intensities at cos and sin of Fraction*0.5*PI accordingly.

Unity

In Unity, the sound intensity in each ear is collected as the camera rotates around in the horizontal plane and looks up and looks down. The resulting graph shows that the panning strength is being applied correctly, resulting in a smooth audio experience.

Horizontal Camera Vector	Volume intensity polar plot

Web Audio (W3C)

In Web Audio, the PannerNode "equalpower" Panning is implemented using a simple and relatively inexpensive algorithm. The azimuth is to the angle of the listener facing forwards, and anything outside of the -90 to 90 region is behind the listener and mirrored to the front.

if (azimuth < -90)
    azimuth = -180 - azimuth;
else if (azimuth > 90)
    azimuth = 180 - azimuth;

if (azimuth <= 0)
    x = (azimuth + 90) / 90;
else
    x = azimuth / 90;

gainL = cos(x * Math.PI / 2);
gainR = sin(x * Math.PI / 2);

Proposed Implementation for Godot

Based on the analysis of the issue and the comparison with other platforms, we propose a solution for the Godot engine. The solution is to implement the stereo panning using the same algorithm as Unreal Engine and Unity. This will ensure that the panning strength is applied correctly, resulting in a smooth audio experience.

// inputs
Vector3 to_source;
Vector3 listener_up;  // eg (0,1,0)
Vector3 listener_ear; // eg (1,0,0)

// calculation
Vector3 to_source_projected = to_source - listener_up*(listener_up.dot(to_source));
float cos_asimuth = listener_ear.dot(to_source_projected)/to_source_projected.length();
float cos_asimuth_by_two = sqrt(cos_asimuth + 1)/2); // using cos(t) = 2*cos(t/2)^2 - 1
return cos_asimuth_by_two;

More Advanced Implementations

All these platforms have the facility for a more advanced HRTF (Head-Related Transform Function) implementation. However, UE and Unity do it with a plugin extension, and so should we since it is would otherwise involve some code bloat for a feature that is predominantly required for VR.

Unity seems to implement the panning_strength feature by blending this stereo calculation with the mono (same) value using a lerp, which is a good answer.

Steps to Reproduce

To reproduce the issue, follow these steps:

Create a new project in Godot.
Add an AudioStreamPlayer3D node to the scene.
Set the panning_strength property to 1.
Play the audio and observe the distorted audio experience.

Minimal Reproduction Project (MRP)

The minimal reproduction project (MRP) is available at amplitudepanning.zip.

Q: What is the problem with the current implementation of stereo panning in Godot's AudioStreamPlayer3D class?

A: The current implementation of stereo panning in Godot's AudioStreamPlayer3D class is incorrect, resulting in a distorted audio experience. The panning strength is not being applied correctly, causing the audio to sound unnatural.

Q: What is the expected behavior of stereo panning in Godot's AudioStreamPlayer3D class?

A: The expected behavior of stereo panning in Godot's AudioStreamPlayer3D class is to apply the panning strength correctly, resulting in a smooth and natural audio experience.

Q: How does the current implementation of stereo panning in Godot's AudioStreamPlayer3D class differ from other platforms?

A: The current implementation of stereo panning in Godot's AudioStreamPlayer3D class differs from other platforms in that it does not apply the panning strength correctly. Other platforms, such as Unreal Engine and Unity, implement stereo panning correctly, resulting in a smooth and natural audio experience.

Q: What is the proposed solution for the problem with the current implementation of stereo panning in Godot's AudioStreamPlayer3D class?

A: The proposed solution for the problem with the current implementation of stereo panning in Godot's AudioStreamPlayer3D class is to implement the stereo panning using the same algorithm as Unreal Engine and Unity. This will ensure that the panning strength is applied correctly, resulting in a smooth and natural audio experience.

Q: What are the benefits of implementing the proposed solution for the problem with the current implementation of stereo panning in Godot's AudioStreamPlayer3D class?

A: The benefits of implementing the proposed solution for the problem with the current implementation of stereo panning in Godot's AudioStreamPlayer3D class are:

Improved audio quality: The proposed solution will ensure that the panning strength is applied correctly, resulting in a smooth and natural audio experience.
Increased accuracy: The proposed solution will use the same algorithm as Unreal Engine and Unity, ensuring that the panning strength is applied correctly.
Better compatibility: The proposed solution will ensure that Godot's AudioStreamPlayer3D class is compatible with other platforms, such as Unreal Engine and Unity.

Q: How can I implement the proposed solution for the problem with the current implementation of stereo panning in Godot's AudioStreamPlayer3D class?

A: To implement the proposed solution for the problem with the current implementation of stereo panning in Godot's AudioStreamPlayer3D class, you can follow these steps:

Create a new project in Godot.
Add an AudioStreamPlayer3D node to the scene.
Set the panning_strength property to 1.
Implement the proposed solution using the same algorithm as Unreal Engine and Unity.

Q: What are the potential issues with implementing the proposed solution for the problem with the current implementation of stereo panning in Godot's AudioStreamPlayer3D class?

A: The potential issues with implementing the proposed solution for the problem with the current implementation of stereo panning in Godot's AudioStreamPlayer3D class are:

Complexity: The proposed solution may require additional code and complexity to implement.
Compatibility: The proposed solution may not be compatible with all platforms or devices.
Performance: The proposed solution may affect the performance of the game or application.

Q: How can I troubleshoot issues with implementing the proposed solution for the problem with the current implementation of stereo panning in Godot's AudioStreamPlayer3D class?

A: To troubleshoot issues with implementing the proposed solution for the problem with the current implementation of stereo panning in Godot's AudioStreamPlayer3D class, you can follow these steps:

Check the code: Review the code to ensure that it is correct and implemented correctly.
Test the game or application: Test the game or application to ensure that the stereo panning is working correctly.
Consult the documentation: Consult the documentation for Godot's AudioStreamPlayer3D class to ensure that you are using the correct properties and methods.
Seek help: Seek help from the Godot community or a professional developer if you are experiencing issues with implementing the proposed solution.