Echo Cancellation Chip
EC CHIP
The Adaptive Digital Technologies echo canceller chip is a carrier-class ITU G.168-2002 compliant PCM network echo canceller chip. The solutions are based upon Adaptive Digital's AT&T certified soft echo canceller running on the Texas Instruments TMS320C6424 (HD - High Density), 'C5507, and 'C5510 digital signal processors.
| EC Chip | |||
| Part Number | DEVICE | PORTS | DTMF |
| EC-C5507-4 | C5507 | 4 | |
| EC-C5507-8 | C5507 | 8 | |
| EC-C5510-12 | C5510 | 12 | |
| EC-C5510-24 | C5510 | 24 | |
| EC-C5510-32 | C5510 | 32 | included |
| EC-N-24 | C6424 | 24 | preliminary |
| EC-N-48 | C6424 | 48 | |
| EC-N-64 | C6424 | 64 | |
The ADT EC Chip supports both T-1 and E-1 configurations.
The EC Chip uses two TDM serial ports, one for the receive side of the canceller and the other for the send side of the canceller. The TDM serial ports are fully programmable to allow connection to nearly any type of serial bus.
The EC Chip includes Adaptive Digital's proprietary voice quality enhancement algorithms including noise reduction and automatic level control. These features, in conjunction with the echo canceller, ensure maximum voice quality.
CHANNEL DENSITY |
||||
 |
Echo Canceller |
Echo Canceller with
Noise Reduction and Automatic Level Control |
||
|
T-1 Spans |
E-1 Spans |
T-1 Spans |
E-1 Spans |
32 msec. tail |
9 |
7 |
4 |
3 |
64 msec. tail |
7 |
6 |
3 |
2 |
128 msec. tail |
5 |
4 |
2 |
2 |
EC Off |
N/A |
N/A |
6 |
4 |
TABLE: 1
Control of the EC Chip is facilitated by using an ANSI "C" set of API functions that are provided to run on the host processor. These functions configure and control the EC Chip as well as return status information to the host application.
FEATURES
- Certified by AT&T Voice Quality Lab
- ITU G.168-2002 Compliant
- Compliant using all ITU hybrid models
- Low Throughput Delay (500 microseconds)
- Supports up to 240 channels
- Adaptive Non-linear processor
- Comfort Noise Generator
- Operates in SS-7 Networks
- No divergence due to double-talk
- G.164/G.165 Tone Disabler
- Noise Reduction
- Programmable "Aggressiveness"
- Adapts to background noise continuously
- Automatic Level Control
- Programmable maximum gain/loss
- Programmable Output Target Level
CHIP CONFIGURATION
The EC Chip needs to be configured at power up. Configuration parameters for the serial ports, echo canceller, automatic level control, and noise reduction are described in the sections that follow.
SERIAL PORT CONFIGURATION
The EC Chip can operate using either one or two TDM serial ports. Although time slot mapping can be done, there are default time slot mappings for both the single port and the two port configurations. If two serial ports are used (ports 0 and 1), a single echo canceller channel operates on a given time slot on both serial ports. For example, echo canceller channel 0 is connected to serial port 0, time slot 0 for its receive side and it is connected to serial port 1, time slot 0 for its send side. If a single serial port is used, the receive and send sides use even and odd time slots. In this case, the receive side would be connected to serial port 0, time slot 0 and the send side would be connected to serial port 0, time slot 1
In order to interface to a wide variety of serial TDM busses, the EC Chip serial port configuration is programmable. Table 1 below describes the serial port configuration parameters.
Serial
Port Characteristics |
||
PARAMETER |
VALID RANGE |
DEFAULT VALUE |
Serial Port 0 |
Enabled/Disabled |
Enabled |
Serial Port 1 |
Enabled/Disabled |
Enabled |
Number of Time Slots |
0..255 |
128 |
Use Standard Mapping |
True / False |
True |
Data Format |
u-Law, A-Law, 8 bit Linear, or 16 bit
Linear |
u-Law |
Transmit Sync Polarity |
Active High or Active Low |
Active High |
Receive Sync Polarity |
Active High or Active Low |
Active High |
Transmit Clock Polarity |
Rising Edge or Falling Edge |
Rising Edge |
Receive Clock Polarity |
Rising Edge or Falling Edge |
Falling Edge |
Transmit Data Delay |
0 to 2 |
1 |
Receive Data Delay |
0 to 2 |
1 |
DX Pin Delay |
Enable or Disable |
Disable |
TABLE: 2
ECHO CANCELLER CONFIGURATION
The echo canceller algorithm has numerous programmable options to allow it to be configured appropriately for a wide variety of applications. When bi-directional cancellation is selected, the canceller is independently programmable in each direction. Table 3 lists the echo canceller configuration parameters.
Echo Canceller
Configuration Parameters |
||
PARAMETER |
VALID RANGE |
DEFAULT VALUE |
Global Echo Canceller Enable |
Enabled/Disabled |
Enable |
Tail Length |
32, 64, and 128 milliseconds |
128 |
NLP Type |
Off, Mute, Random Noise, or Hoth Noise |
Hoth Noise |
NLP Threshold |
12, 18, 24 dB |
24 |
CNG Threshold |
-40..-60 dBm |
-43 dBm |
Double TalkThreshold |
0 to 12 (units of dB) |
4 |
G.165 Detect Enable |
Enable or Disable |
Enable |
Adapt Enable |
Enable or Disable |
Enable |
Number of reflectors |
1 to 3 - The initial value can not
be exceeded at run time. |
3 |
Reflector Length |
4, 8, 12, 16 milliseconds |
8 |
TABLE: 3 Echo Canceller Configuration Parameters
Note that the tail length affects the channel density of the chip.
Automatic Level Control Configuration
ALC Configuration Parameters |
||
PARAMETER |
VALID RANGE |
DEFAULT VALUE |
Global ALC Enable |
Enabled/Disabled |
Enable |
Target Power |
-30 to 0 (units of dBm) |
-18 |
Loss Limit |
-23 to 0 (units of dB) |
-10 |
Gain Limit |
0 to 23 (units of dB) |
10 |
Table 4 lists the configuration parameters that control the operation of the Automatic Level Control (ALC) feature.
Echo canceller channels are turned on and off as needed under control of a host processor. Each time a channel is turned on, it is necessary to provide call setup information. Since an echo canceller is a two port device, we define the two ports as side A and side B. The canceller can be configured to cancel echo in neither, one, or both directions. If echo cancellation is enabled at the A side, the echo perceived by the speaker at the B side will be cancelled. If echo cancellation is enabled at the B side, the echo perceived by the speaker at the A side will be cancelled.
CHANNEL SET-UP
Channel
Setup Parameters |
||
PARAMETER |
VALID RANGE |
DEFAULT VALUE |
A Side Serial Port |
0.1 |
|
A Side Time Slot |
0..255 |
|
B Side Serial Port |
0.1 |
|
B Side Time Slot |
0..255 |
|
Enable A Side EC |
Enable/Disable |
Enable |
Enable B Side EC |
Enable/Disable |
Disable |
Table 5: Channel Setup Parameters
If the EC Chip is configured for standard serial port mapping, the B side time slot will be derived from the A side time slot.
Online Control and Status Reporting In order to perform diagnostics and testing, a number of controls are provided to modify the state of an active channel.
Channel
Control Parameters |
||
PARAMETER |
VALID RANGE |
DEFAULT VALUE |
EC Enable |
Enable/Disable |
Global |
EC Adapt Enable |
Enable/Disable |
Enable |
EC NLP Enable |
Enable/Disable |
Enable |
EC CNG Enable |
Enable/Disable |
Enable |
ALC Enable |
Enable/Disable |
Global |
Noise Reduction Enable |
Enable/Disable |
Global |
Table: 6 lists the features that be controlled during an active call.
PARAMETER |
VALID RANGE |
Convergence Status |
0..32767 |
G.165 Tone Detector
Status |
Null, G.164 Active, G.165
Active |
Table: 7 lists the status parameters that are available during an active call.
EC Chip ANSI "C" API
Control of the EC Chip is facilitated by using an ANSI "C" set of API functions that are provided to run on the host processor. These functions configure and control the EC Chip as well as return status information to the host application.
