British Telecommunications Public Limited Company

Paul C Millar

Alan J Greaves

Robert Bp Carpenter

Ian R Cameron

Method and apparatus for operating a telephone exchange having

A speech recognition system comprises a recogniser (2) for receiving speech signals from users. The recogniser (2) compares each received word with templates of words stored in a reference template store (3) and flags each template that corresponds most closely to a received word. The flagged templates are stored in a template store (11). The recogniser (2) compares the speech pattern from a given user of a second utterance of a word for which a flagged template is already stored in the template store (11) with the templates stored in the reference template store (3) and with the flagged templates in the template store (11), so as to produce a second flagged template of that word. The second flagged templates are also stored in the template store (11). Sifting means (21) analyse a group of flagged templates of the same word, and produce therefrom a second, smaller group of templates of the word. These templates are stored in another template store (22).

Speech recognition

Speaker verification using memory address

A pair of filters (H.sub.1 H.sub.2) split an input signal into two frequency sub-bands (defined by a transition frequency) which are down-sampled and coded: after sample rate restoration the signals are filtered (K.sub.1 K.sub.2) and combined. To reduce signal delays, the delay response of each filter is non-constant, having a maximum at or beyond the transition frequency. Preferably non-quadrature filter pairs are used. Filters may be cascaded for more than two sub-bands.

Sub-band coders, decoders and filters

A 1st-order digital filter network has a quantizer (Q) reducing the number of output bits following multiplication (in M3). The quantizer omits insignificant bits, adding one LSB (boosting) or not (truncating) in dependence on the value of the multiplier output (D).

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Felixstowe, United Kingdom

Paul C Millar