User`s manual

Figure 7-28 Two Channel Adaptive Filter Control Window

Description of controls (Figure 7-28) is as follows:

Filter Size: Used to set the number of FIR filter taps in the adaptive filter. Filter size is indicated

both in taps (filter order) and in milliseconds. Minimum Filter Size is 16 taps, but

can be set to as high as 3600 (Mono Single mode, see Section A-8. ). Normally, the

maximum filter size possible is used in the 2CH adaptive filter

Adapt Rate: Used to set the rate at which the adaptive filter adapts to changing signal conditions

(mathematically known as Mu). A Mu of 1 x 2

-14

provides very slow adaptation,

while a Mu of 256 x 2

-14

provides fastest adaptation. As a rule set this rate to

maximum initially, to establish convergence, then back off to a mid value to maintain

cancellation.

Delay: Sets the number of audio samples in the delay line. Delay is indicated both in

samples and in milliseconds. Minimum Delay is no samples (0), but can be set to

as high as 999 samples.

Adapt Mode: Selects Auto(matic) or Fixed adaptation rate. Auto is recommended. When Fixed

is selected, the specified Adapt Rate Mu is applied to the filter at all times. When

Auto is selected, the specified Adapt Rate is continuously power normalized

depending upon the input signal level. The Auto mode generally results in faster

convergence for a given Mu.

Processor Output: Selects Residue or Filter output. The Residue output is the normal output selection,

which is the signal left over after the Reference signal has been cancelled from the

Primary signal. The Filter output is the modified Reference signal being subtracted

from the Primary signal.

Crash Detect: Activates the built-in “crash” detection feature in the MicroDAC IV. This feature

automatically detects when the adaptive filter has “crashed” and clears the filter.

Checking this box enables this feature.

Reference Reference Compensation automatically adjusts

Compensation: the Reference Level to bring it to an optimal level for cancellation. It can apply a

maximum gain of 18 dB. Checking this box enables this feature.