The key to the integrated EC-VQE solution is putting the various algorithms together in such a way that voice quality enhancement is maximized. Voice Enhancement / Echo Cancellation Chip
Voice Quality Enhancement (VQE) is the umbrella that encompasses the technology intended to improve the voice quality in both the newer as well as the traditional telecommunication systems.
AVAILABILITY
ADT VQE-168 is available off the shelf on the following Platforms: Other configurations are available upon request.
| Product Number | Platform |
| ADT_vqe-ec_c641x | TI TMS320C641X |
DESCRIPTION
The Adaptive Digital Technologies high-density voice enhancement/echo canceller chip (VQE-168) a carrier-class ITU G.168-2002 compliant PCM network echo canceller chip. This solution is based upon Adaptive Digital’s AT&T certified soft echo canceller running on the Texas Instruments TMS320C641X digital signal processor. The VQE-168 supports both T-1 and E-1 configurations.
The VQE-168 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 VQE-168 includes Adaptive Digital’s proprietary voice quality enhancement algorithms including noise reduction, noise suppression, and automatic level control. These features, in conjunction with the echo canceller, ensure maximum voice quality.
The Echo Cancellation VQE Chip Solution integrates the individual algorithms in such a way that voice quality is maximized .
FEATURES
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In order to interface to a wide variety of serial TDM busses, the VQE-168 serial port configuration is programmable. Table 1 below describes the serial port configuration parameters.
| 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 |
Note that the tail length affects the channel density of the chip.
Table: 1
Control of the VQE-168 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 VQE-168 as well as return status information to the host application.
Chip Configuration
The VQE-168 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 VQE-168 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
| 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 2: Echo Canceller 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 3: Serial Port Characteristics.
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 2 lists the echo canceller configuration parameters.
Automatic Level Control Configuration
Table 4 lists the configuration parameters that control the operation of the Automatic Level Control (ALC) feature.
| 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 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 VQE-168 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. Table 6 lists the features that be controlled during an active call. Table 7 lists the status parameters that are available during an active call.
| 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.
VQE-168 ANSI “C” API
Control of the VQE-168 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 VQE-168 as well as return status information to the host application.
FUNCTION
VQE168Configure( .. )
VQE168SetupChannel( … )
VQE168TeardownChannel( … )
VQE168ControlChannel( … )
VQE168GetChannelStatus( … )
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