3.1. Voice Features Supported

The D/42 Series PBX boards use a dual-processor architecture comprising a DSP (Digital Signal Processor) and a general purpose microprocessor to handle all voice processing functions. This dual processor approach off loads many low-level decision making tasks from the host computer.

When a D/42-xx system is initialized, firmware is downloaded from the host PC to the firmware RAM and DSP memory on the D/42-xx board. This downloadable firmware gives the board all of its intelligence and enables easy feature enhancement and upgrades. Based on this, the D/42-xx can perform the following operations on incoming calls:

• automatically control the volume of the incoming audio signal
• record and compress the incoming audio voice signal. Sampling rates and coding methods are selectable on a channel by channel basis
• detect the presence of tones - DTMF, or an application defined signal or dual tone
• perform call progress analysis to determine the state of an incoming call.

For outbound calls, the D/42-xx can perform the following:

• play stored compressed audio files
• adjust the volume and speed of playback upon application or user request
• generate tones - DTMF, or an application defined signal or dual tone.

The D/42-xx board is basically a D/41D board with specialized PBX circuitry replacing the analog front end. The D/42-xx boards perform features available on a D/41D as well as emulate phones connected to a PBX.

When recording speech, the D/42-xx can use different digitizing rates from 24 to 64 Kb/s (Kilobits per second) as selected by the application for the best speech quality and most efficient storage. The digitizing rate is selected on a channel-by-channel basis and can be changed each time a record or play function is initiated. The processed speech is stored on the host PC's hard disk. When playing back a stored file, the voice information from the host PC is passed to the D/42-xx where it is converted into analog voice signals for transmission to the PBX.

The on-board control processor controls all operations of the D/42-xx board via a local bus and interprets and executes commands from the host PC. This processor handles real-time events, manages data flow to the host PC to provide faster system response time, reduces PC host processing demands, processes DTMF and PBX signaling before passing them to the application, and frees the DSP to perform signal processing. Communications between this processor and the host PC is via the shared buffer memory that acts as an input/output buffer and thus increases the efficiency of disk file transfers. This shared buffer memory interfaces to the host PC via the XT/AT bus.

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