Digital Voice Systems AMBE-3000 Specifications download pdf (Page 57)

AMBE-3000™ Vocoder Chip Users Manual

Version 2.8, August, 2011

O Management

resp

onse between microphone/speaker and the digital PCM interface to the vocoder, as shown in Figure 26 Typical Vocoder

plementation. This includes any analog electronics plus the A-to-D and D-t

o-A converters as well as any digital filtering

performed prior to the voice encoder or after the voice decoder.

Figure 26 Typical Vocoder Implementation

The AMBE+™ voice encoder and decoder operate with unity (i.e. 0 dB) gain. Consequently the analog input and output gain

elements shown in Figure 27 Vocoder Front End are only used to match the sensitivity of the microphone and speaker with the

A-t

o-D converters and D-to-A converters, respectively.

Figure 27 Vocoder Front End

It is recommended that the analog input gain be set such that the RMS speech level under nominal input conditions is 25 dB

below the saturation point of the A-to-D converter (+3 dBm0). This level, which equates to -22 dBm0, is designed to provide

sufficient margin to prevent the peaks of the speech waveform from being clipped by the A-to-D converter.

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Digital Voice Systems AMBE-3000 Specifications Page 57