True digital sound in GSM-cards for Asterisk

New GSM-cards for Asterisk (with support for WCDMA/UMTS) are now capable of digital sound processing. This improvement provides higher quality of speech, clear sound with no interferences or noises. Technically, it means the sound from radio-module sent to the system already in digital form i.e. the sound already digitized by the module itself.

It is still possible to switch to analogue sound mode by sending special AT-command to each radio-module from Asterisk console. Switching to digital sound currently supported only by cards with the support of WCDMA/UMTS, but they still can be used in regular GSM-networks (without UMTS).