A directional microphone arrangement has a number of discrete microphones each having an electrical output and elements for deriving first and second electrical signals which are 180.degree. out of phase with respect to each other from the outputs of the microphones. A third signal is also derived through differentiation from one of the microphone outputs which is 90.degree. out of phase with respect to one of the first or second signals. All of the first, second and third signals are added in a summing unit, the output of the summing unit forming the output for the arrangement.

An audio signal recording system comprising a first apparatus for generating a sum signal of left and right signals of a stereophonic audio signal and a difference signal of the left and right signals, and a second apparatus for recording on a recording medium the sum signal and the difference signal which have been generated by the first apparatus, without converting the sum signal and difference signal into the left and right signals.

A plurality of microphones are disposed on a body to detect the speech of a speaker. First, second and third microphones may respectively detect the sounds emanating from the speaker's mouth, nose and throat and produce signals representing such sounds. A fourth microphone may detect the fricative and plosive sounds emanating from the speaker's mouth and produce signals representing such sounds. The signals from the different microphones are compared to allow the discrimination of certain speech sounds. For example, a high amplitude of the signal from the nose microphone relative to that from the mouth microphone indicates that a nasal sound such as m, n, or ng was spoken. Identifying signals are provided to the speech recognition system to aid in identifying the speech sounds at each instance. The identifying signals can also select a microphone whose signal can be passed on to the recognition system in its entirety. Signals may also be provided to identify that spoken words such as "paragraph" or "comma" are actually directions controlling the form, rather than the content, of the speech by the speaker. The selected signals, the identifying or classifying signals and the signals representing directions may be recovered by the system of this invention. The selected and identifying signals may be processed to detect syllables of speech and the syllables may be classified into phrases or sentences. The result may then be converted to a printed form representing the speech or utilized in the operation of another device.

A hearing aid having a stereophonic microphone mounted on a flexible base and an adhesive for adhering it to the top of the head. This substantially eliminates the shadow effect encountered when two separate hearing aids are used, one for each ear, which reduces the ability of the wearer to locate the source of sounds originating at an angle from a vertical central plane passing through the nose and axis of the wearer.

A gradient directional microphone system (100) and method therefor includes no more than three microphones (101, 103, 105) and a processor (107). Each of the microphones (101, 103, 105) have substantially the same gradient order (135, 137, 139) and frequency response. Each microphone produces an electrical signal (109, 111, 113) that is responsive to sound pressure (119, 121, 123) at each microphone (101, 103, 105). The processor (107) is coupled to receive the electrical signal (109, 111, 113) from each microphone (101,103, 105), and operative to produce an output signal (131) for the gradient directional microphone system (100) having a gradient order (141) at least two gradient orders higher than the gradient order (135, 137, 139) of each of the microphones (101, 103, 105). Using the present invention, the size and complexity of the gradient directional microphone system (100) is substantially reduced over that of the prior art.