Signal-predictive audio transmission system

#A portion of the disclosure of this patent application, including the accompanying compact discs, contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of this patent document or the patent disclosure as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights.

#Although audio signals are often transmitted in digital form, analog transmission remains attractive for many applications, particularly where bandwidth and dynamic range constraints of the transmission channel limit the potential data rate of digital transmission. Audio encoding schemes have been developed that permit audio transmission at lower data rates, but the data rate reduction is typically accompanied by various drawbacks. These include digital signal processing complexity, degraded audio quality, encoding and decoding delays, and abrupt performance degradation with weakening signals.

#Conventional analog transmission techniques can efficiently convey the frequency spectrum of an audio signal without the excess bandwidth of high digital data rates or the disadvantages associated with data rate reduction. Such techniques require strong signals to preserve high audio dynamic range, however, which is ultimately limited by noise in the analog transmission circuitry. This problem is often mitigated by “companding” the signal.

#Various embodiments of the present invention are described below with reference to the drawings, wherein like designations denote like elements.

#FIG. 1 is a schematic block diagram of a wireless microphone transmitter and receiver employing signal-predictive audio transmission according to various aspects of the invention.

#FIG. 2 is a signal flow diagram of signal processing functional modules implemented by a signal-predictive audio transmission system of the invention.

#A signal-predictive audio transmission system according to various aspects of the present invention provides numerous benefits, including substantial psychoacoustic reduction in perceived noise levels and enhancement of dynamic range, without significant audio degradation of the type conventionally associated with companding. Such a system can be advantageously implemented wherever such benefits are desired. For example, wireless microphone system 100 of FIG. 1 includes a transmitter 110 that receives an audio input signal at a microphone 111 and sends a compressed error signal to a receiver 150, in accordance with various aspects of the invention.

#The error signal that transmitter 110 sends to receiver 150, which travels via field radiation over wireless link 15, is not directly based on the actual audio input signal. (Indeed, it is barely recognizable if listened to directly, in many implementations.) Rather, the error signal is representative of amplitude-compressed deviations between the input signal and an extrapolation that transmitter 110 computes based on the input signal.

#Wireless microphone system 100 and other exemplary embodiments of the invention may be better understood with reference to FIGS. 1-36, the detailed description below, the 296-line program listing immediately following the detailed description, and the program modules on two compact discs labeled COPY 1 and COPY 2 that accompany this application. The program listing and the program modules are incorporated herein by reference and form an integral part of this specification. Both compact discs include the ASCII program module files listed below in TABLE I and TABLE II using the reference identifiers “A” through “Z.”