Re: [Discuss-gnuradio] Broadcast FM is crap!

[Tim Pozar]

Up until about 20 years ago when digital stereo generation started be perfected 
and for a period after that, providing good stereo separation better than 40 dB 
was pretty hard.  I developed an early digital stereo generator in 1979 that 
provided about 55 dB but much of that was dependent on the low pass filter that 
I had to have after the generator in order to reduce third harmonic products of 
38 Khz.   I ended up putting a third order Butterworth filter in the unit.  I 
also had to consider ringing as you really need to minimize this in order to 
prevent over-modulation.

More modern stereo generators such as Aphex's digicoder and Bob Orban's and 
Frank Foti's boxes provide stellar stereo separation now as everything is in 
the digital domain.

The main problem with lack of stereo information or L-R content is the original 
material and the how the material is processed for air.  Once upon a time, 
music was mixed with the home stereo environment in mind.  It sounded great.  
Early on many companies went way overboard on stereo mixing (ie Decca) where 
the staging was just too wide and very little energy was in the L+R domain.

That changed in the 70s and 80s when more aggressive broadcast 
compression/limiting was available and in use by AM and FM stations.  I have 
run into many a mix engineer that would add compression and limiting in order 
to "try" to have better control of what the music sounds like over-the-air.   A 
pretty standard procedure for these folks is to have a little bootleg 
transmitter at a studio with an Orban or Omnia processor  in front of it.  They 
will play back the cut they are working on and run out to a car and see how the 
mix sounds.   There are even a series of "craptactular" speakers that you can 
buy and sit on your mixing desk that will mimic the low-fidelity sound systems 
in most cars.

So, radio stations are pushing recording engineers to process their music 
poorly and radio stations are creating their own cesspool of audio by each 
trying to sound "louder" than each other.  All of this means that the less 
information you put in L-R the better.

Tim Pozar
Past Chief Engineer of to many stations to list here and usually ones that were 
the softest on the dial.

On Feb 19, 2012, at 9:46 AM, Andrew Davis wrote:

> The is a lot of really cool reasons for the stereo to be the way it
> is, check out http://transmitters.tripod.com/stereo.htm  it's an
> amazing read.
> 
> Also the problem of no stereo signal is probably with modern music,
> there is not much difference between L and R anymore, just a single
> channel of mass produced noise, so since the're subtractive, silence
> is broadcast on the L-R signal, not like days past when Pink Floyd
> would fly you though space on both channels!
> 
> On Sun, Feb 19, 2012 at 11:50 AM, Marcus D. Leech <address@hidden> wrote:
>> Spent some time yesterday evening building up a stereo FM receiver in GRC.
>>  I know there are already a few of these for broadcast FM,
>>  but for personal education reasons, I thought I'd build something up.
>> 
>> Attached is my result.
>> 
>> It seems to work reasonably well (better than the existing example WFM
>> stereo receiver on the same signals).
>> 
>> But something I've discovered is that about 30% of the program material
>> coming out of my fave radio station doesn't even have
>>  any L-R signal present.  I mean, I can understand during announcements,
>> commercials, etc.   But a lot of the musical material
>>  doesn't have any L-R, even modern material.
>> 
>> But I never really knew the gory details of FM Multiplex before--didn't know
>> the L-R channel was DSB-SC, for example.  Never had cause
>>  to think deeply about it.  I knew there was a 19kHz pilot tone, and that it
>> was doubled to 38kHz (usually with a PLL), but I always thought
>>  it was used as a switching signal of some sort.
>> 
>> If I get keen, I'll extend this to include RDS decoding.
>> 
>> --
>> Marcus Leech
>> Principal Investigator
>> Shirleys Bay Radio Astronomy Consortium
>> http://www.sbrac.org
>> 
>> 
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