[asterisk-users] Audiocodes MP-114 noise

[Jessee J Holmes]

Jason,

First, before you start reading, get to the latest firmware from  
Audiocodes (MP118_SIP_F4.80A.034.004.cmp), there have been  
significant echo improvements in this version.

After many days of working with Audiocodes on this problem and much  
time spent here by multiple technicians trying to reproduce and  
resolve this issue; this morning, Atacomm received an email from  
Audiocodes with a full explanation to this now confirmed issue with  
all MP-11x units. Atacomm will immediately begin work on a KB article  
within our website that confirms this issue and outlines the  
manufacturer recommended steps to resolve this problem.

Apparently, there have been some changes with the MP-11x's that can  
negatively affect line noise and echo.  Below are some steps which  
can help to correct these problems:

1. The new design did away with the Coefficent file.  Audiocodes, now  
instead, introduced a configurable parameter called  
countrycoefficient. This parameter can be adjusted to a specific  
country based on known configurations.  For the most part this should  
work.  70(USA) is the default value.  More can be found in the User’s  
manual.

2.  In just about every case, an FXO is added to a Pre-existing PBX  
or CO line, you can expect echo. This comes from the fact that delay  
(IP Network) is being introduced, and what used to be Side tone is  
now delayed so much it is echo. Just about every difference on the  
line that can be heard between the pre fxo and post fxo installation  
can be traced to echo, or line quality issues.

3.  Going forward, Audiocodes would like to suggest that when  
installing the product do the following:

A) Make sure the Line coming from the PBX or CO is a Loop Start line.  
Ground start is not supported on the MP-11x series of gateways. (The  
M1K FXO will in 5.0)

B) Check that the Line can deliver for a 600 Ohm Impedance line

-52 to -24 V of Off Hook Voltage

-15 to -6 V of  On Hook Voltage

20 to 35 ma of loop current.

If you know the line is not 600 Ohm, please gather metrics on the  
line, and the make and model of the PBX or switch it is attached too,  
plus country of origin. If it is not from the USA, please look up the  
country of origin and then find the CountryCoefficient to match this.  
Load the .ini file to the board with this setting and reset.  Make  
sure the Gateway has a firmware version of 4.60.035 or higher or  
4.80.030 or higher.

C) Put the device on the network with Voice Volume set to 0 and input  
gain set to 0. Make calls, if there is no issue, you can stop here.   
However, Echo is still expected most of the time.

D) The echo should be heard by the IP side participant as their voice  
is reflected back.  If this is the case, then what needs to be done  
is to lower the voicevolume (IP—TEL). This way the speaker’s  
reflected voice will comeback low enough for the ECAN to cancel it  
out (-6 is usually recommended as the value to plug in here). A  
little experimentation is needed as the loss for all lines will vary  
based on length from the CO. Echo is usually taken care of in this  
manner.

E) The incoming speaker from the PSTN’s voice seems low, set  
InputGainLocation =1, and then slowly increment the Input Gain  
Parameter(TelàIP) to adjust for this. In past releases (see the note  
about loads above), the input gain was always applied prior to the  
ECAN which had the effect of amplifying the returned echo and noise  
on the line causing crosstalk and clipping issues. This is no longer  
the case.

If the above does not resolve the issues, then you need to go ahead  
and collect DSP, Ethereal and Syslog traces along with the board.ini,  
these are to be sent to your support agent, who will then send these  
to Audiocodes for their engineers to evaluate.  This should not  
happen often.


Jessee Holmes
Atacomm / Ataractic Corporation
www.atacomm.com
V: 1-877-700-VOIP
jholmes at atacomm.com

Looking for voice over IP products?  Visit our VoIP store at http:// 
voipstore.atacomm.com/

On Nov 3, 2006, at 12:14 AM, Jason Kim wrote:
Jessee,
I tried many combinations of "Voice Volume", "Input
Gain" and packetization time , but it's noisy steel.
I'm using G.711A-law and packetization time is 20ms.
It can be impedance mismatch problem but i cannot
adjust impedance of FXO port of MP-114.
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