private void UpdateOcclusion()
        {
            var hasOcclusionOn = GrpVariation.UsesOcclusion;

            if (!hasOcclusionOn)
            {
                if (!_occlusionOnLastFrame)
                {
                    return;
                }

                _occlusionOnLastFrame = false;
                MasterAudio.StopTrackingOcclusionForSource(GrpVariation.GameObj);
                ResetToNonOcclusionSetting();

                return;
            }

            _occlusionOnLastFrame = true;

            if (_listenerThisFrame == null)
            {
                // cannot occlude without something to raycast at.
                return;
            }

            if (Time.realtimeSinceStartup - _occlusionLastCalculated <= MasterAudio.ReOccludeCheckTime)
            {
                // too early, abort and try next frame
                return;
            }

            var lastCalcTime = Time.realtimeSinceStartup;

            if (_occlusionLastCalculated == FakeNegativeFloatValue)
            {
                // spread out the line casts so they're not all on the same frame (for ambient sounds that all start in the Scene).
                lastCalcTime += MasterAudio.ReOccludeCheckTime * Random.Range(0f, 0.9f);
            }

            _occlusionLastCalculated = lastCalcTime;

            var direction          = _listenerThisFrame.position - Trans.position;
            var distanceToListener = direction.magnitude;

            if (distanceToListener > VarAudio.maxDistance)
            {
                // out of hearing range, no reason to calculate occlusion.
                MasterAudio.AddToOcclusionOutOfRangeSources(GrpVariation.GameObj);
                ResetToNonOcclusionSetting();
                return;
            }

            MasterAudio.AddToOcclusionInRangeSources(GrpVariation.GameObj);

            if (GrpVariation.LowPassFilter == null)
            {
                // in case Occlusion got turned on during runtime.
                GrpVariation.gameObject.AddComponent <AudioLowPassFilter>();
            }

                        #if UNITY_4_5 || UNITY_4_6 || UNITY_4_7 || UNITY_5_0 || UNITY_5_1
                        #else
            var is2DRaycast = _maThisFrame.occlusionRaycastMode == MasterAudio.RaycastMode.Physics2D;

            var oldQueriesStart = Physics2D.queriesStartInColliders;
            if (is2DRaycast)
            {
                Physics2D.queriesStartInColliders = _maThisFrame.occlusionIncludeStartRaycast2DCollider;
            }
                        #endif

            var   hitPoint    = Vector3.zero;
            float?hitDistance = null;
            var   isHit       = false;

            if (_maThisFrame.occlusionUseLayerMask)
            {
                switch (_maThisFrame.occlusionRaycastMode)
                {
                case MasterAudio.RaycastMode.Physics3D:
                    RaycastHit hitObject;
                    if (Physics.Raycast(Trans.position, direction, out hitObject, distanceToListener, _maThisFrame.occlusionLayerMask.value))
                    {
                        isHit       = true;
                        hitPoint    = hitObject.point;
                        hitDistance = hitObject.distance;
                    }
                    break;

                case MasterAudio.RaycastMode.Physics2D:
                    var castHit2D = Physics2D.Raycast(Trans.position, direction, distanceToListener, _maThisFrame.occlusionLayerMask.value);
                    if (castHit2D.transform != null)
                    {
                        isHit       = true;
                        hitPoint    = castHit2D.point;
                        hitDistance = castHit2D.distance;
                    }
                    break;
                }
            }
            else
            {
                switch (_maThisFrame.occlusionRaycastMode)
                {
                case MasterAudio.RaycastMode.Physics3D:
                    RaycastHit hitObject;
                    if (Physics.Raycast(Trans.position, direction, out hitObject, distanceToListener))
                    {
                        isHit       = true;
                        hitPoint    = hitObject.point;
                        hitDistance = hitObject.distance;
                    }
                    break;

                case MasterAudio.RaycastMode.Physics2D:
                    var castHit2D = Physics2D.Raycast(Trans.position, direction, distanceToListener);
                    if (castHit2D.transform != null)
                    {
                        isHit       = true;
                        hitPoint    = castHit2D.point;
                        hitDistance = castHit2D.distance;
                    }
                    break;
                }
            }

#if UNITY_4_5 || UNITY_4_6 || UNITY_4_7 || UNITY_5_0 || UNITY_5_1
#else
            if (is2DRaycast)
            {
                Physics2D.queriesStartInColliders = oldQueriesStart;
            }
#endif

            var endPoint  = isHit ? hitPoint : _listenerThisFrame.position;
            var lineColor = isHit ? Color.red : Color.green;

            if (_maThisFrame.occlusionShowRaycasts)
            {
                Debug.DrawLine(Trans.position, endPoint, lineColor, .1f);
            }

            if (!isHit)
            {
                // ReSharper disable once PossibleNullReferenceException
                MasterAudio.RemoveFromBlockedOcclusionSources(GrpVariation.GameObj);
                ResetToNonOcclusionSetting();
                return;
            }

            MasterAudio.AddToBlockedOcclusionSources(GrpVariation.GameObj);

            var ratioToEdgeOfSound = hitDistance.Value / VarAudio.maxDistance;
            var filterFrequency    = AudioUtil.GetOcclusionCutoffFrequencyByDistanceRatio(ratioToEdgeOfSound);

            // ReSharper disable once PossibleNullReferenceException
            GrpVariation.LowPassFilter.cutoffFrequency = filterFrequency;
        }
        /// <summary>
        /// This method is called in a batch from ListenerFollower
        /// </summary>
        /// <returns></returns>
        public bool RayCastForOcclusion()
        {
            DoneWithOcclusion();

            var raycastOrigin = Trans.position;

            var offset = RayCastOriginOffset;

            if (offset > 0)
            {
                raycastOrigin = Vector3.MoveTowards(raycastOrigin, _listenerThisFrame.position, offset);
            }

            var direction          = _listenerThisFrame.position - raycastOrigin;
            var distanceToListener = direction.magnitude;

            if (distanceToListener > VarAudio.maxDistance)
            {
                // out of hearing range, no reason to calculate occlusion.
                MasterAudio.AddToOcclusionOutOfRangeSources(GrpVariation.GameObj);
                ResetToNonOcclusionSetting();
                return(false);
            }

            MasterAudio.AddToOcclusionInRangeSources(GrpVariation.GameObj);
            var is2DRaycast = _maThisFrame.occlusionRaycastMode == MasterAudio.RaycastMode.Physics2D;

            if (GrpVariation.LowPassFilter == null)
            {
                // in case Occlusion got turned on during runtime.
                var newFilter = GrpVariation.gameObject.AddComponent <AudioLowPassFilter>();
                GrpVariation.LowPassFilter = newFilter;
            }

            var oldQueriesStart = Physics2D.queriesStartInColliders;

            if (is2DRaycast)
            {
                Physics2D.queriesStartInColliders = _maThisFrame.occlusionIncludeStartRaycast2DCollider;
            }

            var oldRaycastsHitTriggers = true;

            // ReSharper disable once ConvertIfStatementToConditionalTernaryExpression
            if (is2DRaycast)
            {
                oldRaycastsHitTriggers       = Physics2D.queriesHitTriggers;
                Physics2D.queriesHitTriggers = _maThisFrame.occlusionRaycastsHitTriggers;
            }
            else
            {
                oldRaycastsHitTriggers     = Physics.queriesHitTriggers;
                Physics.queriesHitTriggers = _maThisFrame.occlusionRaycastsHitTriggers;
            }

            var   hitPoint    = Vector3.zero;
            float?hitDistance = null;
            var   isHit       = false;

            if (_maThisFrame.occlusionUseLayerMask)
            {
                switch (_maThisFrame.occlusionRaycastMode)
                {
                case MasterAudio.RaycastMode.Physics3D:
                    RaycastHit hitObject;
                    if (Physics.Raycast(raycastOrigin, direction, out hitObject, distanceToListener, _maThisFrame.occlusionLayerMask.value))
                    {
                        isHit       = true;
                        hitPoint    = hitObject.point;
                        hitDistance = hitObject.distance;
                    }

                    break;

                case MasterAudio.RaycastMode.Physics2D:
                    var castHit2D = Physics2D.Raycast(raycastOrigin, direction, distanceToListener, _maThisFrame.occlusionLayerMask.value);
                    if (castHit2D.transform != null)
                    {
                        isHit       = true;
                        hitPoint    = castHit2D.point;
                        hitDistance = castHit2D.distance;
                    }

                    break;
                }
            }
            else
            {
                switch (_maThisFrame.occlusionRaycastMode)
                {
                case MasterAudio.RaycastMode.Physics3D:
                    RaycastHit hitObject;
                    if (Physics.Raycast(raycastOrigin, direction, out hitObject, distanceToListener))
                    {
                        isHit       = true;
                        hitPoint    = hitObject.point;
                        hitDistance = hitObject.distance;
                    }

                    break;

                case MasterAudio.RaycastMode.Physics2D:
                    var castHit2D = Physics2D.Raycast(raycastOrigin, direction, distanceToListener);
                    if (castHit2D.transform != null)
                    {
                        isHit       = true;
                        hitPoint    = castHit2D.point;
                        hitDistance = castHit2D.distance;
                    }

                    break;
                }
            }

            if (is2DRaycast)
            {
                Physics2D.queriesStartInColliders = oldQueriesStart;
                Physics2D.queriesHitTriggers      = oldRaycastsHitTriggers;
            }
            else
            {
                Physics.queriesHitTriggers = oldRaycastsHitTriggers;
            }

            if (_maThisFrame.occlusionShowRaycasts)
            {
                var endPoint  = isHit ? hitPoint : _listenerThisFrame.position;
                var lineColor = isHit ? Color.red : Color.green;
                Debug.DrawLine(raycastOrigin, endPoint, lineColor, .1f);
            }

            if (!isHit)
            {
                // ReSharper disable once PossibleNullReferenceException
                MasterAudio.RemoveFromBlockedOcclusionSources(GrpVariation.GameObj);
                ResetToNonOcclusionSetting();
                return(true);
            }

            MasterAudio.AddToBlockedOcclusionSources(GrpVariation.GameObj);

            var ratioToEdgeOfSound = hitDistance.Value / VarAudio.maxDistance;
            var filterFrequency    = AudioUtil.GetOcclusionCutoffFrequencyByDistanceRatio(ratioToEdgeOfSound, this);

            var fadeTime = _maThisFrame.occlusionFreqChangeSeconds;

            if (fadeTime <= MasterAudio.InnerLoopCheckInterval)   // fast, just do it instantly.
            // ReSharper disable once PossibleNullReferenceException
            {
                GrpVariation.LowPassFilter.cutoffFrequency = filterFrequency;
                return(true);
            }

            MasterAudio.GradualOcclusionFreqChange(GrpVariation, fadeTime, filterFrequency);

            return(true);
        }