21

¡ Semiconductor

ML7021

EXPLANATION OF TERMS

Attenuating Function :

This function prevents howling and controls the noise level with

the attenuator for the RIN input and SOUT output. Refer to the

explanation of pins (ATT pin).

Echo Attenuation :

If there is talking (input only to RIN) in the path of a rising echo

arises, the echo attenuation refers to the difference in the echo

return loss (canceled amount) when the echo canceler is not used

and when it is used.

Echo attenuation = (SOUT level during through mode operation)

– (SOUT level during echo canceler operation) [dB]

Echo Delay Time :

This is the time from when the signal is output from ROUT until

it returns to SIN as an echo.

Acoustic Echo :

When using a hands free phone, and so on, the signal output from

the speaker echoes and is input again to the microphone. The

return signal is referred to as acoustic echo.

Telephone Line Echo :

This is a signal which is delayed midway in a telephone line and

returns as an echo, due to reasons such as a hybrid impedance

mismatch.

Gain Control Function :

This function prevents howling and controls the sound level with

a gain controller for the RIN input. Refer to the explanation of pins

(GC pin).

Center Clipping Function : This function forces the SOUT output to a minimum value when

the signal is below –54 dBm0. Refer to the explanation of pins

(NLP pin).

Double Talk Detection :

Double talk refers to a state in which the SIN and RIN signals are

input simultaneously. In a double talk state, a signal outside the

echo signal which is to be canceled can be input to the SIN input,

resulting in misoperation.

The double talk detector prevents such misoperation of the canceler.

Howling Detection :

This is the oscillating state caused by the acoustic coupling between

the loud speaker and the microphone during hands free talking.

Howling not only interferes with talking, but can also cause in

misoperation of the echo canceler.

The howling detector prevents such misoperation and prevents

howling.

Echo Return Loss (ERL) :

When the signal output from ROUT returns to SIN as an echo, ERL

refers to how much loss there is in the signal level during ROUT.

ERL = (ROUT level) – (SIN level of the ROUT signal which returns

as an echo) [dB]

If ERL is positive (ROUT > SIN), the system is an attenuator

system.

If ERL is negative (ROUT < SIN), the system is an amplifier system.