1. Technical Field
The present invention relates broadly to improvements in tactile sensing of acoustic and audio signal for hearing impaired persons. The invention has particular, although not exclusive, utility in enhancing the ability of hearing impaired persons to enjoy the audio portion of television signals.
2. Discussion of the Prior Art
Tactile devices for the deaf have been studied for approximately sixty years, and within the last eight years have been produced as commercial items. The essential concept embodied in all of these devices is to convert sound signals into vibrations that can be felt on the skin via the tactile sense. Naturally enough, the greatest emphasis has been on the ability to recognize speech sounds, although the practical value of recognizing various background sounds, such as bells, footsteps and so on, are also well appreciated. Since the tactile sensory system is unable to perceive vibrations much above 800 to 1000 Hz, and since significant input from signals to at least 4000 Hz is required to impart important speech data, a significant portion of the research and development work in this field has addressed methods for processing sound signals such that information from the higher frequencies can be transmitted to a user. Virtually all work in the field has focused on wearable devices which can be used on a more or less continuous basis; accordingly, a further constraint has been that the methods chosen result in small, cosmetically acceptable designs. Using these guidelines, the kinds of systems that have evolved all use small skin transducers, worn either on the wrist, chest or around the back of the neck. While it is well known that placing the transducers somewhere on a hand yields very good perceptual results, these locations are avoided for reasons relating to utility. Typically these transducers are resonant at a single frequency, usually 250 Hz as this is the most sensitive frequency for the tactile sense, and processing methods are employed that encode the desired signals at this rate. In the more advanced systems a number of such transducers are used, each being assigned to a different portion of the acoustic frequency band and worn at a respective position on the skin. Thus, in these systems, the incoming sound signal is separated by a processor into spectral segments, each segment being represented at a respective location on the skin as a 250 Hz signal with a varying time envelop and intensity according to the spectral content of the original signal.
The most advanced of these so-called "multiple channel" tactile devices currently available use seven such transducers arranged side by side with channels divided to cover the sound frequency range from 200 Hz to 7000 Hz, divisions being selected according to data on vowel frequencies commonly known in the speech discipline. The processing arrangement permits no more than two transducers to be actuated at the same time. It has been found that this method is desirable both to provide clarity of perception and to conserve battery life.
The reason for using resonant transducers is that they are more efficient than wideband transducers, at least as regards presently available technology. This, in turn, allows compact battery supplies to provide reasonably long operation with attendant cosmetic acceptability, but only at the cost described below.
It has been recognized that wideband transducers allow more easily perceived patterns with richer information content to be applied to the skin. In particular there are certain sound information components, notably voicing data in speech and attack waveform data in music, that are better represented by direct presentation of the unprocessed signals for the lower frequency range of the incident sound signal. This is true for that portion of these signals lying between about 50 Hz to 800 Hz; frequencies above this tend to be so dimly perceived by the tactile sense that there is little if any information communicated without some kind of encoding being used, such as the transducer location encoding described above.
It may be that improved perception could be obtained with a hybrid system using a similar multiple channel scheme wherein the lower frequency channels use no encoding, being excited directly by the lower spectral portion of the original sound signal, and only the upper band spectral components are encoded as described above. However, the technical methods for obtaining such a system in wearable form are not currently available in a configuration that also meets cosmetic requirements.
On the other hand, if one relaxes the cosmetic requirements, as would be appropriate for the intended uses of the present invention, then broadband transducers such as loudspeakers or small motors, as described hereinbelow, provide a means for supplying the desired direct tactile representations of lower frequency sounds.
In order to provide a frame of reference, it is desirable to note the specifics of the narrowband transducers currently used in the tactile field. A typical unit is approximately one inch long by 0.5 inch thick by 0.7 inch wide and weighs about seven grams. Its low weight and flat configuration is appropriate for the usual methods of mounting. Since all signals applied to such a transducer are encoded at a single frequency, typically 250 Hz, requirements for bandwidth are only related to the required response time. A well designed unit follows waveform changes at better than a 20 msec rate, adequate for virtually all speech sounds and all environmental sounds of interest. For such a device a typical peak driving energy to obtain maximum perceptual feel is on the order of 350 mw. It has been found over a period of years of actual use that the average duty cycle for these kinds of systems is on the order of 0.2. Accordingly, for a wearable system using one such transducer, the expended energy/hour is on the average about 70 mwatt-hours. A typical rechargeable battery pack used to power these devices, constrained in size according to the usual cosmetic considerations, stores about 1600 mwatt-hours. Hence, as is verified in many thousands of hours of actual use, a system using one such transducer will operate, on the average, for about twenty-three hours between charges. Generally, the decrease in hours of operation between charges does not follow linearly with an increasing number of transducers because, depending on design parameters, it is not true that all transducers in a system have the same duty cycle. For the seven channel device mentioned previously, where only two transducers at most are activated simultaneously, the time of operation between charges is approximately 15 hours.
In contrast, a typical mass-produced small motor requires about 1.5 watts in the application mode described herein to elicit the same perceptual intensity; it weighs about forty grams and has a cylindrical configuration typically on the order of one inch in diameter and one inch in length. It is clear that neither the configuration nor the power requirements lend themselves to application in a wearable form and that the weight also mitigates against this use. However, for a hand-held or hand-contact application in which larger size is allowable and hence a larger space can be allocated for the battery pack, the use of such small motors is not precluded. If loudspeakers are utilized, they require only 350 mw to achieve the same level drive for the applications described herein; however the loudspeakers are typically even larger and heavier than the small motors. Again, for hand-held or hand-contact applications this larger size and weight is not objectionable.
From the foregoing it will be appreciated that the present invention is intended to teach the use of small mass-produced motors or loudspeakers in tactile transducers for the deaf and hearing impaired in those applications where large size and low efficiencies, as compared to the usual tactile transducers, are not serious detriments. In particular, but not exclusively, this would apply to transducing television audio signals whether or not accompanied by captioning.
The present invention has particular, but not exclusive, utility in conjunction with television programming incorporating closed captioning or similar techniques employed to provide titling on the video screen to represent spoken words in the audio signal. The closed captioning titling technique is described and defined in Report No. E-7709-C, revised May 1980, by the Public Broadcasting Service. The disclosure in that report is expressly incorporated herein. Typically, a closed captioning decoder processes the closed captioning signal that is included in line twenty-one of the NTSC video signal. Decoding results in titling that is overlayed on the television screen, the titling content corresponding to speech in the audio portion of the received television signal. The present invention, by providing a low cost wideband transducer that can be used in conjunction with closed captioning, not only enhances appreciation of television programs for hearing impaired persons; it also permits such persons to be trained in the use of the transducers since the speech signals being tactually transduced are simultaneously viewed as titling on the television screen.