How many sounds can play all at once?

I've found that if you try to play more than 20 sounds at the same time through an audiosource / audiosources unity will stop playing audio entirely.

One technique that is simple is to count how many sounds you are playing and what their duration is, when they stop playing (using clip.length) uncount the sound. If the amount of sounds playing is more than 20 deny any new sounds from playing until less than 20 sounds are playing.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 /*
     really simple audio manager, to stop unity audio from crackling or becoming inaudible
 
     hawken king 2016
 
  */
 
 public class AudioPlayer : MonoBehaviour {
 
     public static AudioPlayer instance;
     public AudioSource audioSource;
     int playing;
     void Start() 
     {
         instance = this;
     }
     public void PlayAudio(string clip)
     {
         if (playing > 20) return;
         StartCoroutine(Playclip(clip));
     }
     IEnumerator Playclip(string clip)
     {
         playing++;
         AudioClip a = Resources.Load("Audio/"+clip) as AudioClip;
         audioSource.PlayOneShot(a);
         yield return new WaitForSeconds(a.length);
         playing--;
     }
 }

This depends on your hardware. See the AudioSource.priority documentation:

Unity is virtualizing AudioSources, when there's more AudioSources playing than available hardware channels. The AudioSources with lowest priority (and audibility) is virtualized first. Priority is an integer between 0 and 256. 0=highest priority, 256=lowest priority