09-05-2011, 12:16 PM
Digital voice processing chips withdifferent features and coding techniquesfor speech compression andprocessing are available on the marketfrom a number of semiconductor manufacturers.Advanced chips such as Texasinstruments’ TMS320C31 can implementvarious voice-processing algorithms includingcode-excited linear prediction, adaptivedifferential pulse-code modulation, A law(specified by California Council for InternationalTrade), μ law (specified by BellTelephone) and vector sum-excited linearprediction.On the other hand, APR9600 singlechipvoice recorder and playback devicefrom Aplus Integrated Circuits Fig. 1 shows the functional blockdiagram of IC APR9600. Complete chipmanagement is accomplished throughthe device control and message controlblocks.Voice signal from the microphone (seeFig. 2) is fed into the chip through a differentialamplifier. It is further amplifiedby connecting Ana_Out (pin 21) to Ana_In(pin 20) via an externalDC blocking capacitor C1.A bias signal is applied tothe microphone and to savepower during playback, theground return of this biasnetwork can be connectedto the normally open sideof the record switch. BothMic.in and Mic.Ref (pins 18and 19) must be coupled touse of a proprietary analogue storagetechnique implemented using flash nonvolatilememory process in which each cellis capable of storing up to 256 voltage levels.This technology enables the APR9600to reproduce voice signals in their naturalform.The APR9600 is a good standalonevoice recorder or playback IC with nonvolatilestorage and playback capability for32 to 60 seconds. It can record and playmultiple messages at random or in sequentialmode. The user can select sample rateswith consequent quality and recordingtime trade-off. Microphone amplifier, automaticgain control (AGC) circuits, internalanti-aliasing filter, integrated output amplifierand messages management are someof the features of the APR9600 chip.
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