Cone of Silence

How to build a more sensitive cell-phone or create a cone of silence

One of the biggest problems with microphones and other sound capture devices is discriminating between the desirable sounds and the undesirable sounds. The microphone just captures the good sound and the bad noise in one signal. Many engineers have developed a number of sound filtering techniques for removing noise from the signal.
This invention describes a mechanism for filtering out sound by identifying the location of the sounds and then excluding the sounds that comes from unwanted locations. This is sort of like the cone of silence in the television show "Maxwell Smart".
Such a device would be particularily useful in cellular phones. Many people often raise their voices when speaking on a cell phone in the hope of speaking above the noise nad increasing the clarity of the sound that reaches the other end of the conversation. The loud voices are often annoying to others in the same area. A location-based sound capture device would allow the cell phone to keep only the sound produced close to the handset. The other noise would be filtered out.
Of course, the invention is not limited to cell phones. Plain, old everyday phones can also use the technique when noise intrudes.

There are a number of sophisticated mechanisms for determining the location of sounds. Naval engineers, for instance, use arrays of microphones to track submarines. There are sophisticated solutions that can take the input from the multiple microphones and convert it into the locations of the sources.
The microphones can be arranged in a number of different arrangements. Generally, more microphones increase the accuracy of the information if they are arranged on different planes. A simple solution uses four microphones placed on the corners of a tetrahedron, but it may be possible to use fewer in some situations.
The software discovers the location of the sounds by comparing the time that the sounds arrive at each microphone. This can be accomplished by shifting the signal from each microphone a bit and then comparing them. When the strongest sound are identified, they can be removed and the algorithm applied to the weaker sound that remain. More sophisticated algorithms exist for distinguishing between echoes and removing many of the other effects that cloud signals.
The mathematics could be implemented with a relatively low-cost digital signal processor already present in cellular phones and other electronics. The processor could use the spatial information about the location of the sounds to filter the signal thus producing a more capable cell phone or sound capture device.

The technique does not need to be limited to simply distinguishing between speakers and eliminating unwanted noise. One person may require a distinct kind of filtering than another and a sophisticated version of a speaker phone could use the algorithm to identify the speaker and apply the appropriate modifications to their words. It might possible, for instance, to translate one person's voice automatically but not anothers.

-- October 19,2000