CS6403 datasheet(47/54 Pages) CIRRUS

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Performance Measurements

ERLE

Echo Return-Loss Enhancement (ERLE) is de-

fined as the amount of attenuation in echo that

the echo canceller provides, usually expressed in

decibels. In general, half-duplex should be dis-

abled for ERLE measurement.

For best case performance, a sine wave is an

ideal far-end input signal.

Provide a -6dBFS

sine wave at 1kHz to the far-end input (the SSI

in Mode 2 or the far-end codec in Mode 1). It

should come out the SPKROUT and couple to

MICIN. The signal at MICIN will then be pre-

sent at the far-end output.

Measure this with

coefficients cleared (RMS voltage is suggested).

Measure again after the echo canceller has

adapted (coefficients in normal mode). The dif-

ference between the decibel value of the two is

the ERLE in dB.

To test with real speech, use an easily repeatable

speech sample.

Capture the non-cancelled

speech with a Digital Storage Oscilloscope that

can calculate RMS voltage. Do the same for the

cancelled speech.

There should be a delay of

about five seconds of far-end speech before mak-

ing the measurement to ensure that the echo

canceller has time to adapt.

Convergence Time

Convergence is loosely defined to be the state at

which the echo canceller has adapted sufficiently

to render the echo inaudible. Therefore, conver-

gence time may be defined as the time required

for convergence from cleared coefficients.

Convergence time may be measured using the

Digital Storage Oscilloscope approach men-

tioned above. Once a level of attenuation which

defines convergence has been chosen, a compari-

son of the pre-canceller and post-canceller

voltage levels should indicate when convergence

occurs.

Half-Duplex

The half-duplex mode of the echo canceller is

provided as a fail-safe mechanism to ensure

communication in situations where the echo can-

celler is not providing enough ERLE for good

quality conversation. To freeze the CDB6403 in

half-duplex mode, push the "HD ON" switch and

move the switch to the "CLEAR" position.

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CDB6403

DS192DB3

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