[App_rpt-users] usb radio config file

[Ken]

subsequent experimentation seems to indicate that if  you set
txprelim=yes        
the audio overloading of the CM108 goes away.

I guess you get pre-emphasis AND limiting
or nothing at all

which is too bad because even though it says

; no - Audio is not pre-emphasized and limited.
; Suitable for use on a microphone input

once the signal has been trashed, it is not really suitable for 
anything, especially a microphone input.

a better wording might be

Audio is not pre-emphasized and NOT limited
if audio level exceeds D/A dynamic range it will be severely distorted.
the user needs to make sure that levels do not exceed the maximum
warning: some of the pre-recorded GSM files exceed the maximum

It would be nice if there was an option for limiting with no 
re-emphasis ...

Ken
-----Original Message-----
From: hwstar at rodgers.sdcoxmail.com
To: David Powell-Williams <dpowellwilliams at shaw.ca>; 
app_rpt-users at qrvc.com
Sent: Tue, Jan 5, 2010 6:55 pm
Subject: Re: [App_rpt-users] usb radio config file


>
> From: "David Powell-Williams" <dpowellwilliams at shaw.ca>
> Date: 2010/01/05 Tue PM 03:26:26 PST
> To: <app_rpt-users at qrvc.com>
> Subject: [App_rpt-users]  usb radio config file
>
> <snip>
> Second issue:  The loudest playback sounds cause the URI to go into
> saturation and distort. I may not have calibrated the levels very 
carefully,
> but even if I manually lower the txlevel setting from 800 down to, 
say, 300
> it still distorts - it's just a quieter distortion. What can cause 
this?
> <snip>
>
> I have the same problem with a modified CM108 usb installation.
>
> After setting all the 'radio tune' parameters, there is serious 
distortion
> on voice modulation peaks, irrespective of the source being Iaxrpt or
> another node.
>
> However, the 'radio tune txvoice' generates a perfect sine wave at 3 
KHz
> deviation, as seen on an oscilloscope at the exciter modulator or on a
> service monitor off-air.  I am using duplex=0 in rpt.conf since the 
node
> operates simplex.
>
> Dave
> VE7MQ
> 2140
>
> _______________________________________________
> App_rpt-users mailing list
> App_rpt-users at qrvc.com
> http://qrvc.com/mailman/listinfo/app_rpt-users
>


I have not seen this on a properly configured system. Chances are it 
has to do with de-emphasis configuration on the receive side, or 
pre-emphasis/limiting (prelim) in the transmit side)

Where is the audio getting distorted? Transmit or receive?
so you see the distortion on the TX line or RX line if you look with a 
scope?

You might be able to determine where it is getting distored by 
connecting your node to a working node you can monitor,  then send 
audio both ways.

Disclaimer: I offer URI support and suggestions as a courtesy only as I 
do not derive any income from sales of the URI. I am in no way 
obligated to provide support at any level.

Steve
WA6ZFT


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