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  Coherence filtering and coherence enhancement
HEAD VISOR - Features - Coherence Filtering and Enhancement
HEAD VISOR allows the user to feed additional channels into the data stream as a reference. In real time, HEAD VISOR determines their Coherence with the current microphone signals and removes the incoherent or coherent signal components. Any sensor with ICP or Line level can be used as reference (e.g. microphones, acceleration sensors, laser vibrometers etc.).
   
Working with coherence filtering/ enhancement
The picture on the right shows two incoherent sound sources (loudspeakers). Another source is visible on the wall. (Figure 1)
 
Figure 1 (source mapping without filtering)
Coherence enhancement
(of the right sound source)
A microphone is used as reference. If the microphone is placed close to the right sound source, HEAD VISOR enhanced the coherent components, and the source map no longer shows the incoherent left sound source nor its mirror source on the wall. (Figure 2)
Right Figure 2 (coherence enhancement)
The source mapping of HEAD VISOR, using the microphone as reference, only shows signals coherent with the right sound source. (Move the mouse over the picture to see the scenario without filtering.)
 
Coherence enhancement
(of the left sound source)
If the reference sensor is placed close to the left source, the right source disappears. The source at the wall remains visible and can thus be identified as a coherent mirror source. (Figure 3)
Right Figure 3 (coherence enhancement)
The source mapping of HEAD VISOR, using the microphone as reference, only shows signals coherent with the left sound source.
 
Coherence filtering
(of the right sound source)
If the procedure is repeated with coherence filtering, the source located near the reference sensor disappears. (Figure 4)
Right Figure 4 (coherence filtering)
The source mapping of HEAD VISOR, using the microphone as reference, only shows signals incoherent with the right sound source.)
 
Coherence filtering
(of the left sound source)
With the coherence filtering of the left sound source, the source located near the reference sensor disappears. Again, the mirror source can be identified. (Figure 5)
Right Figure 5 (coherence filtering)
The source mapping of HEAD VISOR, using the microphone as reference, only shows signals incoherent with the left sound source.
 
Identification of hidden sources
Another typical application of coherence filtering/ coherence enhancement is the detection of hidden sources. For this purpose, a reference sensor is placed close to the dominant source, so this source is attenuated by coherence filtering. Now sources that were masked before due to the limited plot dynamic range become visible. (Figure 6)
Right Figure 6 (without filtering)
The source map of HEAD VISOR shows the above scenario again without filtering. The right sound source has been attenuated and is almost invisible due to the limited plot dynamic range.
 
Right Figure 7
(coherence filtering of the scenario in figure 6)
The coherence filtering of the left (dominant) sound source makes the right (attenuated) sound source clearly identifiable.
 
Right Figure 8
(coherence filtering of the scenario in figure 6)
It is also possible to place the reference sensor near the mirror source.
 
   
 
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