RALCWI Vocoder
CMX608/CMX618/CMX638
5.4.
Overall Signal Latency
Figure 14 Overall Signal Latency
The overall latency of a signal through an encoder/decoder pair is shown diagrammatically in Figure 14.
5.5.
Vocoder Data Format and Bit Order
Packets of both raw and FEC protected Vocoder data are transferred between the device and the host
microprocessor over the byte-wide streaming C-BUS registers. The following sections describe how the
data is organised for the various configurations.
5.5.1.
Packets of Raw Vocoder Frames
The device can produce encoded voice at two different bit rates: 2400bps and 2750bps. The higher the bit
rate, the more bits per 20ms are produced. These bits are packed into bytes for transfer over the C-BUS.
For each bit rate, some of the bits produced are more sensitive to corruption and some are less sensitive.
For applications where the in-built FEC protection is not going to be used, perhaps because the user
already has an existing FEC system, the bits should be encapsulated in such a way that those which are
more sensitive to corruption have the greatest protection. The bits in a frame are named B0, B1, B2 …
etc.
2014 CML Microsystems Plc
20
D/608_18_38/11
CMLMICRO [ CML MICROCIRCUITS ]
