Microphone, gain value and spectrum values do not sync using Unity - unity3d

Question

I am making a simple voice visualization program. My goals are:
Playback microphone input
Visualize voice spectrum and gain in real time
Here is my code:
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
public class VisualizeVoice : MonoBehaviour
{
private const int NUM_SPECTRUM_SAMPLES = 256;
private const int NUM_SPECTRUM_BARS = 32;
private const int NUM_PCM_SAMPLES = 16000;
private const float BAR_DROP_SPEED = 1e-3f;
private const int NUM_SAMPLES_TO_AVERAGE = 8;
private string _deviceName;
private float[] _spectrumData = new float[NUM_SPECTRUM_SAMPLES];
private float[] _fPCMData = new float[NUM_PCM_SAMPLES];
private float _gain = 0;
private AudioClip _audio; // Audio from microphone
private AudioSource _playback; // To play the audio from microphone
// For visualization
private GameObject[] _spectrumBars = new GameObject[NUM_SPECTRUM_BARS];
private GameObject _gainBar;
// Start is called before the first frame update
void Start()
{
if (Microphone.devices.Length == 0) {
Debug.LogError("No Microphone");
return;
}
_deviceName = Microphone.devices[0];
Debug.Log("Current microphone is " + _deviceName);
if ((_playback = this.GetComponent<AudioSource>()) == null) {
_playback = this.gameObject.AddComponent<AudioSource>();
}
_playback.loop = true;
_playback.bypassEffects = true;
_playback.bypassListenerEffects = true;
_playback.bypassReverbZones = true;
_playback.priority = 0;
_playback.pitch = 1;
_playback.clip = _audio = Microphone.Start(_deviceName, true, 1, AudioSettings.outputSampleRate);
// Sync microphone and playback, but it always fails
float waitTime = 0;
while (!(Microphone.GetPosition(_deviceName) > 0) && waitTime <= 2)
waitTime += Time.deltaTime;
if (waitTime > 2) {
Debug.LogError("time out waiting for microphone");
}
_playback.Play();
InitVisualization();
}
// Update is called once per frame
void Update()
{
// Get PCM data and calculate gain
var audioPosition = Microphone.GetPosition(_deviceName);
_audio.GetData(_fPCMData, audioPosition);
UpdateGain();
// Get spectrum data
_playback.GetSpectrumData(_spectrumData, 0, FFTWindow.BlackmanHarris);
// Update visualization
UpdateVisualization();
}
private void InitVisualization()
{
// Initialize spectrum bars
for (int ibar = 0; ibar < NUM_SPECTRUM_BARS; ibar++) {
_spectrumBars[ibar] = GameObject.CreatePrimitive(PrimitiveType.Cube);
_spectrumBars[ibar].transform.parent = this.transform;
_spectrumBars[ibar].transform.localPosition = new Vector3(ibar, 0, 0);
_spectrumBars[ibar].transform.localScale = new Vector3(1, 0, 1);
}
// Initialize gain bar
_gainBar = GameObject.CreatePrimitive(PrimitiveType.Cube);
_gainBar.transform.parent = this.transform;
_gainBar.transform.localPosition = new Vector3(-5, 0, 0);
_gainBar.transform.localScale = new Vector3(4, 0, 1);
// Overall dimension
this.transform.localScale = new Vector3(0.2f, 10.0f, 0.2f);
}
private void UpdateVisualization()
{
// Update spectrum bars
int nSamplesPerBar = NUM_SPECTRUM_SAMPLES / NUM_SPECTRUM_BARS;
for (int ibar = 0; ibar < NUM_SPECTRUM_BARS; ibar++) {
// Calculate value of each bar
float value = 0;
for (int isample = 0; isample < nSamplesPerBar; isample++) {
value += _spectrumData[ibar * nSamplesPerBar + isample];
}
value /= nSamplesPerBar;
// Use current value if increasing, or slowly drop previous value if decreasing
float prevValue = _spectrumBars[ibar].transform.localScale.y;
if (value < prevValue)
value = prevValue - BAR_DROP_SPEED;
// Y scale is set to value
_spectrumBars[ibar].transform.localScale = new Vector3(1, value, 1);
}
// Update gain bar
_gainBar.transform.localScale = new Vector3(4, _gain, 1);
}
private void UpdateGain()
{
_gain = 0;
for(int i = 0; i < NUM_SAMPLES_TO_AVERAGE; i++) {
_gain += Mathf.Abs(_fPCMData[NUM_PCM_SAMPLES - i - 1]);
}
_gain /= NUM_SAMPLES_TO_AVERAGE;
}
}
Here are my questions:
I can't use while (!Microphone.GetPosition(_deviceName) > 0)); to avoid latency from microphone to speaker. If I use it, my application just freezes. If I add code to allow time-out, it has time-out every time.
The gain bar seems irrelevant with my voice. I don't know if my calculation is right.
I'm not sure if I need to average over multiple samples calculating gains, and how many samples I need to average over. I need this gain value later to detect silent moments and cut audio data.

Answer 1

To 1.
You can. Unity allows to define Start as a Coroutine
private IEnumerator Start()
{
...
}
On this way you can use a non blocking
while (!Microphone.GetPosition(_deviceName) > 0))
{
yield return null;
}