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Re: [Discuss-gnuradio] Stereo gain "hacked"

From: Matt Ettus
Subject: Re: [Discuss-gnuradio] Stereo gain "hacked"
Date: Mon, 13 Feb 2006 17:06:50 -0800
User-agent: Thunderbird 1.5 (X11/20051201)

n4hy wrote:
> The stereo separation is pretty awesome.  However on stations that are
> full quieting with monoaural transmissions, the stereo demultiplexer is
> introducing hiss.    On really strong stations, it is hard to hear.  
> The deemphasis has been removed from the processing chain while I try
> and figure out why I do not get adequate stereo demultiplexing when
> using it.  I will continue to study this until I have the solution.  My
> real jobs right now are a) phased array, b) portaudio, and c) IIR filter
> design but I just love music so much I couldn't resist but this will
> have to slide in priority.  I need to meet Eric/Matt's priority list! 
> One other aggro:  RDS is a bunch of money grubbing bandits.  I've found
> some open source but it will require massage and modification.  What we
> need is some GUI genius to give us a decent skin and then we can display
> the RDS messages as they pass by on our fancy radio!  ;-)   Next after
> getting the hiss down and/or the deemphasis sorted out, will be to
> "squelch" the stereo demux if the pilot is not  strong enough or present.

I seem to remember that the preemphasis on stereo signals is not
performed on the multiplexed signal.  It is actually performed on the
audio components separately, before mixing with the stereo subcarrier.
Therefore deemphasis needs to be done after the stereo part is mixed
back down to baseband.

To me, this is backwards, and is not useful, but I think that is the
standard.  Achilleas sent an email to the list several months ago on
this subject.  He also had a simple implementation that did stereo.


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