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  Setting IRLP Node Audio Levels
Compiled by Mike Morris WA6ILQ
from an email thread on the IRLP YahooGroup
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> On Nov 9, 2007, at 1:20 PM, (deleted) wrote:
> > Recently the connect/disconnect messages on my node are at a very low
> > level. You can barely hear them on the repeater.
> >
> > The wierd part is that once connected, all the audio is ok. THis
> > system is regularly used on nets and the audio to and from from
> > participants on the linked reflectors is good.
> >
> > I haven't had a chance to check things with a service montor yet,
> > maybe this weekend.
> >
> > It seems any wav files played are low.
> First, if ALL wav files, including connect and disconnect messages are  
> playing "too low", this typically means that you've set your audio  
> levels incorrectly.  Stop and read the instructions below, or see the  
> link at the bottom for other methods documented by Randy KC6HUR, which  
> also work relatively well.
> Log into the node while it's not connected anywhere (as the repeater  
> username) and type:
> audiotest
> This file is the reference audio for IRLP, and should be played from  
> your node and your node radio measured for deviation at that time.   
> The deviation should be set from 3.0 to 3.5 kHz for the portion of the  
> audiotest wav file that is 1000 Hz tone.  Dave's voice should be  
> peaking at or slightly above 5 kHz of deviation when measured on a  
> fast-responding deviation meter, and assuming your radio is not  
> hitting it's built-in limiter at 5 kHz (or worse, if the deviation  
> limiter is set below 5 kHz).
> Next, you should attach a service monitor or other calibrated FM  
> signal source that can generate a 1000 Hz tone at 3.5 kHz deviation to  
> your node's receiver, and then connect to the echo reflector:
> decode 9990  [add your prefix if your node uses one]
> Remember, now that you've already set the node's output deviation  
> level -- don't touch it after the audiotest setting above.
> Transmit your tone and then unkey.  When the Echo Reflector echos back  
> the audio, use the instrument to measure what your node is  
> transmitting and note the returned deviation.  If it's coming out of  
> your radio lower than 3.5 kHz, turn up the INPUT audio going INTO the  
> sound card.  If it's above 3.5 kHz deviation, turn down the INPUT level.
> INPUT level is the level your sound card is recording your signal at,  
> and then digitizing it and sending it to the all-digital echo  
> reflector.   The reflector is sending you back the exact same bits  
> you're sending out.
> So if the on-air deviation is different, the thing that needs  
> adjusting at this point is what you are sending (your receiver audio).
> After you get it to send back whatever deviation you're sending in --  
> unhook the signal generator, and you're done.  Leave it alone.
>  From then on, if someone sounds too light or too hot, IT'S THEIR  
> MISCALIBRATED NODE and not your problem.
> Audio levels are all over the place from IRLP nodes.  If you're  
> wanting a good "sanity check" test after you set your node correctly,  
> find someone here on the list who has properly done their node using  
> the above method, and test with them.  Don't trust anything you get  
> from a node unless you know they followed the above procedure.
> If you don't have access to proper test gear for FM work, Randy KC6HUR  
> has documented two other methods to get a calibration job on your node  
> done "as right as possible".  See his website and look for the three  
> methods in the pillar/bar on the right hand side of the screen:
> Besides the "Using a Service Monitor" method, he has also documented  
> the "Poor Man's Method" and the "Bessel-Null Method".
> Okay as a final note, you should be VERY close after the above  
> exercise, but if you're finding that things are a "bit hot" or a "bit  
> low" (it shouldn't be off by much), absolutely leave the INPUT alone  
> now (you've calibrated it as best as you can, and you can test with  
> someone with a similarly-calibrated node and they can tell you how you  
> sound -- if you want to make absolutely sure) and only move the OUTPUT  
> audio slider in aumix.
> Randy's documentation of how to do it correctly with the three  
> different methods he describes are better information than this e-mail  
> or likely anything else you'll get on the list, here.
> It's what one of my Elmer's would say:  "Are you a thinkin' man, or  
> are you a knowin' man?"  Do you THINK your node audio is done right,  
> or did you measure it scientifically and KNOW your audio is done  
> right...?  The latter, is -- of course -- always preferred.
> --
> Nate Duehr, WY0X

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This page originally created and posted on 31-Dec-2008

Article text is © Copyright 2007 Nate Duehr WY0X.
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