Sound.cs

using DG.Tweening;
using UnityEngine;

public static class Sound {
    const float pitchVariance = 0.2f;
    const float volumeVariance = 0.15f;
    static AudioSource GetNewSoundSource() {
        var gameObject = new GameObject();
        Object.DontDestroyOnLoad(gameObject);
        return gameObject.AddComponent<AudioSource>();
    }

    static AudioSource universalSource = null;
    public static void PlayClipUniversal(SoundEffect sound) {
        if (universalSource == null) {
            universalSource = GetNewSoundSource();
        }
        PlayClip(universalSource, sound);
    }

    public static void PlayClip(AudioSource source, SoundEffect sound) {
        if (source == null) {
            Debug.LogError("Trying to play sound with null AudioSource");
            return;
        }
        if (sound == null) {
            Debug.LogError("Trying to play sound with null SoundEffect");
            return;
        }

        var randPitch = Random.Range(sound.pitch - (sound.pitch * pitchVariance), sound.pitch + (sound.pitch * pitchVariance));
        var randVol = Random.Range(sound.volume - (sound.volume * volumeVariance), sound.volume + (sound.volume * volumeVariance));

        source.pitch = randPitch;
        source.PlayOneShot(sound.sound, randVol);
    }

    static AudioSource fadeInOutSource = null;
    public static async void PlayClipFadeInOut(SoundEffect sound, float startTime, float fadeInTime, float totalDuration, float fadeOutTime, float volume = -1f, float pitch = -1f) {
        if (fadeInOutSource == null) {
            fadeInOutSource = GetNewSoundSource();
        }
        if (volume == -1f) volume = sound.volume;
        if (pitch == -1f) pitch = sound.pitch;
        fadeInOutSource.pitch = pitch;
        fadeInOutSource.clip = sound.sound;
        fadeInOutSource.time = startTime;
        fadeInOutSource.Play();
        fadeInOutSource.volume = 0f;
        fadeInOutSource.DOFade(volume, fadeInTime).SetEase(Ease.InCirc);
        await Awaitable.WaitForSecondsAsync(totalDuration - fadeOutTime);
        await fadeInOutSource.DOFade(0f, fadeOutTime).SetEase(Ease.OutSine).AsyncWaitForCompletion();
        fadeInOutSource.Stop();
    }
}