Quetzalcoatl.cs

using System.Collections;
using System.Collections.Generic;
using System.IO;
using UnityEngine;

/*
Possible effects to model:

Attenuation of taps
- Apparent surface area
- angle of incidence

Frequency dependent effects
- Air absorbtion
- material absorption

Architectural/geometrical detail
- stair steps (90 vs. 91)
- stair rails
- outer layers (9)
- top cabin

Diffraction

--

Oh wait, none of that is needed, this just works.
Ah well, mystery solved.
*/

public class Quetzalcoatl : MonoBehaviour
{
    [SerializeField] private AudioClip _impulseClip;

    private const float SpeedOfSound = 321f;
    private int _numStairSteps = 91;

    private AudioClip _resultClip;
    private AudioSource _source;
    
    void Start()
    {
        var stopWatch = System.Diagnostics.Stopwatch.StartNew();

        var impulse = new float[_impulseClip.samples];
        var result = new float[_impulseClip.samples * 4];

        _impulseClip.GetData(impulse, 0);
        
        Vector3 listenPos = new Vector3(0f, 1.5f, 0f);

        for (int i = 0; i < impulse.Length; i++)
        {
            result[i] += impulse[i];
        }

        for (int i = 0; i < _numStairSteps; i++)
        {
            Vector3 stepPos = StepPos(i);

            float roundTripDist = Vector3.Distance(listenPos, stepPos) * 2f;
            float delaySecs = roundTripDist / SpeedOfSound;
            int delaySamples = (int)(_impulseClip.frequency * delaySecs);

            float atten = 1f / _numStairSteps;

            for (int j = 0; j < impulse.Length; j++)
            {
                if (delaySamples + j > result.Length) {
                    Debug.LogError("Oops, result buffer isn't long enough for step reflection: " + i);
                    return;
                }
                result[delaySamples + j] += impulse[j] * atten;
            }
        }

        _resultClip = AudioClip.Create("reflection", result.Length, 1, _impulseClip.frequency, false);
        _resultClip.SetData(result, 0);

        _source = gameObject.AddComponent<AudioSource>();
        _source.clip = _resultClip;

        var filePath = Path.ChangeExtension(Path.Combine(Path.Combine(Directory.GetParent(Application.dataPath).FullName, "SoundOutput"), "render_"+System.DateTime.UtcNow.ToFileTimeUtc().ToString()), "wav");
        Debug.Log("Saving to: " + filePath);
        UnitySpeechToText.Utilities.SavWav.Save(filePath, _resultClip);


        stopWatch.Stop();
        Debug.Log($"Render complete, took: {(stopWatch.ElapsedMilliseconds / 1000f)} seconds");
    }

    private static Vector3 StepPos(int step) {
        const float stepDepth = 0.33f;
        const float stepHeight = 0.33f;

        Vector3 stairStart = new Vector3(0f, 0f, 25f);

        return stairStart + new Vector3(
            0f,
            stepHeight * step,
            stepDepth * step
        );
    }

    void Update()
    {
        if (Input.GetKeyDown(KeyCode.Space)) {
            _source.Play();
        }
    }
}