Manual Aspi EF1210 (page 46 of 112) (English)

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EF1210 U

SER

ANUAL

ESIDUAL

CHO

You may hear residual echo if system levels are not set properly. Improper level set-

tings anywhere in the audio path can introduce nonlinearities that hamper the opera-

tion of the EF1210. If you hear residual echo, one of the following conditions may be

causing the problem.

Reverberation vs.

Echo

Do not confuse the residual echo of remote speech with the reverberation of local

speech. Reverberation of local speech is caused when the speech signal arrives at the

microphone via several paths (the direct path and multiple reflections from surfaces in

the room). This is a local room phenomenon that gives the talker’s voice a hollow or

resonant sound (as heard at the remote end).

Reverberation is not an artifact of the echo canceller. It is mainly affected by the dis-

tance of the microphone from the speech source and by the resonances of the room.

While reverberation can be unpleasant, it is not compensated for by the AEC, which

only removes reflections of remote speech. If the remote end complains that they

hear echo, ensure that they are referring to hearing their own voice and not echoes of

local talkers.

You cannot remove the effects of reverberation by changing the EF1210’s settings,

but you can minimize reverberation by moving microphones closer to talkers and, if

necessary, adding acoustical treatment to the room.

Finding the Source

of Echo

Try muting one channel at a time to see if the echo goes away when a particular chan-

nel is muted. You can mute the channel by using the MUTEI command on the

EF1210 or by muting it on the automixer (turn down volume of the microphone on

mixer or use the logic port control). If you find that the echo goes away when a par-

ticular channel is muted, the microphone may not be calibrated correctly. Check one

or more of the following issues.

Acoustic Gain

The most common cause of poor echo cancellation performance is incorrectly

adjusted acoustic gain. This may be explained as follows. The reference signal seen

by the AEC is sent to the Zone output, where it is amplified and sent to the room loud-

speakers. The loudspeaker audio is coupled into the room microphones acoustically,

through direct and reflected acoustic paths, and perhaps also through mechanical cou-

pling. The microphone signal is then amplified and sent to the AEC as the local

microphone input signal. The acoustic gain of a microphone channel refers to the rel-

ative levels of the signal sent to the Zone output (before any amplification) and the

level of this signal that is reflected as the microphone input (after microphone ampli-

fication).

If the electrical level of the reflected signal picked up by microphone is the same as

the level of the electrical signal sent from the AEC to the Zone output, the acoustic

gain of this microphone channel is said to be 0 dB. If the reflected signal picked up

by the microphone is higher than the level of the signal sent to the Zone output, that

microphone channel has positive acoustic gain. The more positive the acoustic gain,

the harder the AEC must work to determine which signal is an echo and which is a

local speech signal.

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Aspi EF1210 Manual

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