Manual Aspi EF1210 (page 47 of 112) (English)

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ROUBLESHOOTING

ASPI Digital -

The Sound of DSP

Technical Support: 404.892.3200 45

Acoustic Gain

Failure

Acoustic gain failure can be caused through a number of mechanisms:

1. The most common is excessive amplification of the remote (reference) signal at

the local Zone output. This may be explained as follows. If the reference signal

is too low coming into the EF1210, the room audio amplifier will need to be

turned up to compensate and bring the room audio to an acceptable level. For

example, if the reference signal is 12 dB too low (just barely lighting the first

green LED on the R

EMOTE

IGNAL

EVEL

ETER

), the room audio will need to

be amplified by approximately 12 dB to bring it to a reasonable listening level.

This adds 12 dB to the acoustic gain, which will most likely cause it to exceed the

amplifier acoustic gain limit (See “Check Acoustic Gain” on page 31.). This sit-

uation can be remedied by proper calibration of the Reference input signal.

2. Another common cause of acoustic gain failure is excessive microphone amplifi-

cation. For example, if a microphone is "hot" by 6 dB, then the reflections of the

Zone output signal which are picked up by the microphone will be amplified by 6

dB more than necessary. This adds 6 dB to the acoustic gain, which may be suf-

ficient to cause acoustic gain problems. This situation could easily arise if, for

example, the conferencing equipment is set up so that participants are too far

from the microphone. In such a situation, after correct microphone setup the

local microphone audio level may be too low because of the distance from the

talker to the microphone. The microphone audio will most likely also be muddy

and reverberant. The installer or user may try to solve these microphone audio

quality problems by turning up the microphone amplification, thus adding to the

acoustic gain. This problem can be remedied by proper microphone selection

(pickup pattern, directionality) and placement, coupled with proper microphone

calibration.

3. A third common cause of acoustic gain problems is excessive coupling between

loudspeaker audio and microphones. This can be addressed by reducing the

microphone coupling, either by positioning microphones so that their pickup pat-

terns are biased away from the loudspeaker audio (and direct reflections of loud-

speaker audio), repositioning loudspeakers, or reducing the loudspeaker

amplification.

In summary, it can be seen from the above that any amplification applied between the

reference input and the microphone inputs can add to acoustic gain problems. To

avoid problems, ensure that the Reference input signal (as reflected on the R

EMOTE

IGNAL

EVEL

ETER

) is not too low, and the microphone input signal (as reflected

on the I

NPUT

IGNAL

EVEL

ETER

) is not too high. Run the built-in EF1210 Acous-

tic Gain test to verify that you do not have acoustic gain problems (See “Check

Acoustic Gain” on page 31.).

In-Conference

Quick Check

If you experience residual echo problems during a conference, you can quickly check

that the reference and microphone levels are calibrated and not causing acoustic gain

problems by observing the signal level meters as follows.

While the remote end is speaking and everyone on the local end is quiet, observe the

activity on the R

EMOTE

IGNAL

EVEL

ETER

. Remote speech should illuminate the

first yellow (0 dB) LED regularly, and the second (+3 dB) LED occasionally. Step

through the microphone input channels by repeatedly pressing the I

NPUT

ELECT

front panel button while the remote end is speaking (the local end must be silent dur-

ing this check), and observe the activity on the I

NPUT

IGNAL

EVEL

ETER

for each

microphone channel in response to the remote talker. If any microphone channel

exhibits greater signal level activity than that shown on the R

EMOTE

IGNAL

EVEL

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Aspi EF1210 Manual

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