zl50211 Zarlink Semiconductor, zl50211 Datasheet - Page 12

• Manufacturer Part Number: zl50211
• Description: 256 Channel Voice Echo Canceller
• Manufacturer: Zarlink Semiconductor

The patented Advanced NLP provides a number of new and improved features over the original NLP found in
previous generation devices. The differences between the Advanced NLP and the original NLP are summarized in
Table 1.
The NLPSel bit in Control Register 3 selects which NLP is used. A “1” will select the Advanced NLP, “0” selects the
original NLP.
The Advanced NLP uses a new noise ramping scheme to quickly and more accurately estimate the background
noise level. The noise ramping method of the original NLP can also be used. The InjCtrl bit in Control Register 3
selects the ramping scheme.
The NLInc sub-register in Noise Control is used to set the ramping speed. When InjCtrl = 1 (such as with the
Advanced NLP), a lower value will give faster ramping. When InjCtrl = 0 (such as with the original NLP), a higher
value will give faster ramping. NLInc is a 4-bit value, so only values from 0 to F(hex) are valid.
The Noise Scaling register can be used to adjust the relative volume of the comfort noise. Lowering this value will
scale the injected noise level down, conversely, raising the value will scale the comfort noise up. Due to differences
in the noise estimator operation, the Advanced NLP requires a different scaling value than the original NLP.
Important Note: NLInc and the Noise Scaling register have been pre-programmed with G.168 compliant values.
Changing these values may result in undesirable comfort noise performance!
The Advanced NLP also contains safeguards to prevent double-talk and uncancelled echo from being mistaken for
background noise. These features were not present in the original NLP. They can be disabled by setting the
NLRun1 and NLRun2 bits in Control Register 3 to “0”.
1.5
The G.165 recommendation defines the disable tone as having the following characteristics: 2100 Hz (±21 Hz) sine
wave, a power level between -6 to -31 dBm0, and a phase reversal of 180 degrees (± 25 degrees) every
450 ms (±25 ms). If the disable tone is present for a minimum of one second with at least one phase reversal, the
Tone Detector will trigger.
The G.164 recommendation defines the disable tone as a 2100 Hz (+21 Hz) sine wave with a power level between
0 to -31 dBm0. If the disable tone is present for a minimum of 400 ms, with or without phase reversal, the Tone
Detector will trigger.
NLP Selection
Reject uncancelled echo as noise
Reject double-talk as noise
Noise level estimator ramping scheme
Noise level ramping rate
Noise level scaling
Disable Tone Detector
Feature
Table 1 - Comparison of NLP Types
NLPSel (Control Register 3)
NLRun1 (Control Register 3)
NLRun2 (Control Register 3)
InjCtrl (Control Register 3)
NLInc (Noise Control)
Noise Scaling
Zarlink Semiconductor Inc.
Register or Bit(s)
ZL50211
12
NLP Default
Advanced
16(hex)
5(hex)
Value
1
1
1
1
not supported)
not supported)
not supported)
not supported)
Default Value
Original NLP
0 (feature
0 (feature
0 (feature
0 (feature
74(hex)
C(hex)
Data Sheet