AMBE-2000 Digital Voice Systems, Inc., AMBE-2000 Datasheet - Page 46

• Manufacturer Part Number: AMBE-2000
• Description: 2.0 - 9.6 KBPS Single ic For Toll-quality, Low Data Rate, Real Time Speech Compression
• Manufacturer: Digital Voice Systems, Inc.

AMBE-2000™ Vocoder Chip
User’s Manual Version 4.0
For example with an Average-Frame-Interval = .02 (i.e. 20 ms) and a Sample-Rate = 8000, then with 100 parts per million
oscillator accuracy (i.e. Frame-Drift = Sample-Drift = .0001), then above constraint equates to 4 < N < 31.25, and N=30 would
be a reasonable selection. In this case the system would input the specified Slip Control Packet into the AMBE-20X0 vocoder
chip every 30’th frame enabling the vocoder chip to adjust for the actual clock drift.
***RECOMMENDED***
Method 3 - Extended Slip Control with as needed Slip Control Packets
The preferred method for using Slip Control Packets is to monitor the availability of data from the AMBE-2000™ vocoder chip
and to only input Slip Control Packets into the data stream sent to the AMBE-2000™ as needed. Note that for this method slip
control must be enabled (SLIP_EN is high) on the chip. This method provides compensation for the widest range of clock drift
(1.2% or 12000 ppm), with the greatest flexibility in frame-interval and sample-rate timing. In this method the same Slip
Control Packets shown in Table 7D are inserted into the data stream going to the AMBE-2000™. However, unlike in the
Periodic method, the packets are not input at regular intervals but are instead only input to the chip when needed. The
recommended procedure for this Method of Slip Control is for the system to read a packet from the AMBE-2000™ at regular
fixed frame intervals where the fixed interval must be within the range [19.875 – 20.125] ms for a sample rate = 8000 Hz. The
system application should check each word output by the AMBE-2000™ and should continue requesting words from the chip
until the packet Header followed by 23 data words are received. If the words received before the Header word consist of only a
single termination word (0xfffe) then no further action is required. However if two or more termination words are received
prior to the Header then the system should input a Slip Control Packet to the AMBE-2000™ on the next available transmission
into the chip (i.e. the next packet going into the AMBE-2000™ decoder should be a Slip Control Packet). Once this Slip
Control Packet is input into the AMBE-2000™ it will respond within 1-2 frames by advancing the time when packets are ready
for transmission by 125 microseconds. Note that this procedure also may require a small amount of buffering in the system to
account for the fact that the packet my not be ready for some small time (< 125 microseconds) after it is first requested.
DVSI Confidential Proprietary, Subject to Change
Page 46
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