Digital Voice Systems AMBE-3000 Specifikace stáhnout pdf (Strana 52)

AMBE-3000F™ Vocoder Chip Users Manual

Version 3.4, April, 2014

O Management

In th

e above figure packets are transmitted to the AMBE-3000™ Vocoder Chip with a fixed-period of 20 ms. The AMBE-

3000™ Vocoder Chip must receive exactly one channel packet per frame period and the “Packet_Uncertainty_Zone” should be

avoided.

The following figure shows some examples of packet timing that are aperiodic

TX_RDY

“aperiodic packets”

Frame_Interval

n+1

Frame_Interval

n+2

Frame_Interval

n+3

Figure 26 TX_RDY Frame interval Examples

When the AMBE-3000™ Vocoder Chip receives a packet during the “Packet_Uncertain_Zone” it is indeterminate which

frame interval will be assigned to the packet. If the AMBE-3000™ Vocoder Chip does not receive any packets during a frame

interval, then the decoder will fill in the gap by synthesizing a frame of speech using the model parameters from the prior

speech frame. This is known as a frame repeat. If two packets are received during a frame interval then the older channel

packet will be discarded.

Note that infrequent “erasure frames” and “frame repeats” can be acceptable in a system and may be a suitable way to account

for differences in the transmit and receive clocks.

Note that the frame intervals are defined relative to TX_RDY which is assumed to be synchronous with transmitted frames.

5.2.3 I/O Handler in Codec Mode

When the AMBE-3000F™ Vocoder Chip is in codec mode, speech samples are received and transmitted via the codec

interface. In codec mode, the schedule for the encoder is based upon the codec clock or the TXRQST signal, if skew control is

enabled.

(Subject to Change) Page 42

DVSI CONFIDENTIAL PROPRIETARY

1 2 ... 47 48 49 50 51 52 53 54 55 56 57 ... 110 111

Žádné komentáře

Digital Voice Systems AMBE-3000 Specifikace Strana 52