e effective size of the speech storage in the use a CCS system as described above. Currently DPNSS and voice processing system caller prompts and inputs are usually DASS2 CCS schemes are widely used in the UK. DASS2 is curren- compressed before storage and decompressed during replay. Tradi- tly the only way to interface at E1 rates to the BT public Network. tionally achieved by using many simple special purpose chips, the Mercury support DASS2 and a CAS scheme at the moment for speech compression technology has gone full circle. DSPs can be public network access at E1 rates. and are used for compression algorithms. However, the expense and 37/8 Voice processing bulk of this approach for voice processing systems with many lines qualities of the speech against templates corresponding to the words has caused the introduction of special ADPCM chipsets which can to be recognised. compress/decompress 60 channels of speech into 30 channels space. These templates are generated by taking many samples of the These chipsets are widely used in telecommunications transmission words desired from the range of accents likely to be encountered. equipment for compression purposes. These samples are usually processed off-line to create the templates. Currently Continually Variable Slope Digitalisation (CVSD) and Typically between 100 and 200 different speakers are required to Adaptive Differential Pulse Code Modulation are the preferred construct the templates. methods. CVSD is used at a rate between 20kbit/s and 32kbit/s, The quality of speech examined is usually the frequency content ADPCM at 24kbit/s or 32kbit/s (i.e. 3:8 or 2:1 compression). of the spoken word. This extracted information typically corre- ADPCM at 32kbit/s introduces negligible distortions and is gener- sponds to the syllables of the spoken words. ally considered superior to CVSD, although it is more complex and Commonly only isolated words can be recognised. However, expensive to realise. ADPCM has become the preferred com- there are other speech recognition pr