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Re: [HCDX] [ODXA] RE: Voice equalization for short wave broadcasting
Dear amigo Bob Chandler VE3SRE has hit the bullseye right in the middle !!!
After several years of doing Dxers Unlimited, one day the former station
chief
engineer and now senior technical advisor Luis Pruna Amer I.E. and
your´s truly
were talking about the people who listened to my show... Then we ask for
help
from the station´s correspondence department, and Irma Armas the head of the
English section came out with the surprising result that Dxers Unlimited
had been
heard and reported from 162 ¨DX entitities¨of the 192 that have been
reported
to Radio Habana Cuba until that time ( this happened about 5 years ago
or so )
Then Pruna and yours truly agreed to optimize the audio frequency
response curve
for not only voice, but specifically to provide optimum response to my
voice.
We ran many tests using an audio frequency spectrum analyzer , and ended
up with
a pretty nice audio that really punches trough ... The curve cuts down fast
below 250 Hertz, and provides a boost of about 6 dB between 500 and 1500
Hertz
then it is again flat up to 2500 Hertz and from there it goes down with
a very steep
descent of 12 dB per octave at first and then 18 dB per octave later.
THIS IS NOT HI-FI !!! But as Bob Chandler has very well analyzed and brought
to our attention, that type of audio frequency curve shaping ( together
with the use
of a well designed and adjusted audio compressor ) will increase the
possibility of
reception of the program in areas where the signal to noise ratio is not of
the typical broadcast quality ( no less than 26 dB signal to noise ratio
minimm ).
I remember when we used the old Siemens and RFT transmitters for
broadcasting
Radio Havana Cuba on single side band, that the 10 kiloWatts PEP Siemens
provided the coverage of a 100 kiloWatt AM transmitter !!!.
So, although Dxers Unlimited doesn´t make use of the full potential
quality of the
station´s studios. STL´s , fiber optic links and transmitters... I do
intend to keep
using the ¨special for Arnie´s voice¨frequency response curve !!!
73 and DX
Arnie Coro
CO2KK
Host of Dxers Unlimited
Radio Havana Cuba
Bob Chandler escribió:
>
> Hi,
>
> It's interesting to learn a few "tricks of the trade" used in shortwave
> broadcasting from both Arnie and Andy.
>
> Other RHC programming is targetted at a more "general" audience within
> the target area of the transmissions.
>
> However, the "target audience" for "DX'ers Unlimited" tends to be ham
> radio operators and SWL hobbyists i.e. folks who may be listening far
> outside the "target area" and will put up with weak signals that are
> fading in and out under poor propagation conditions or QRM or whatever.
>
> So it makes sense to shape the audio to both fit the audience and the
> individual announcer's voice.
>
> I suppose the audio might sound a little "strange" to someone with an S9
> +20 receive signal in North America, but in let's say...India the audio
> processing techniques make the difference between being heard and not
> being heard.
>
> Of course on a "smaller scale" most ham radio operators play around with
> their audio and speech processor settings. For "ragchewing" you might
> use one setting, but in a ham radio contest you'll usually want some
> more "punchy" audio.
>
> 73
>
> Bob Chandler, VE3SRE
> bob@xxxxxxxxxx <mailto:bob%40ve3sre.com>
> http://www.ve3sre.com <http://www.ve3sre.com>
>
> Free software, free society!
>
> On Sun, 2008-02-10 at 20:50 -0500, Prof. Arnaldo Coro Antich wrote:
> > Dear amigo:
> > After running many tests... we found out what may best be described
> > as
> > an almost
> > optimum setting of the audio frequency response curve that will
> > provide my
> > listeners with the best possible audio ¨punch¨, that is audio that
> > will
> > get trough
> > interference of all kinds...
> > As a bonus, if you remove the lower frequency segment of the audio ,
> > that is from
> > 30 to 250 Hertz, your transmitter won´t waste power modulating that
> > segment
> > of the audio spectrum that provides, according to psychologists and
> > audiologists,
> > practically no useful information for the human to decode voice.
> > Although of less significance, it is also a good idea to introduce a
> > high frequency
> > cut with a 12 or 18 dB per octave slope after 2.7 kilohertz or so...
> > I have heard my shows on short wave under the most difficult
> > reception
> > conditions
> > and the programs came in a lot better than the other shows recorded
> > with
> > the ¨standard¨studio quality.
> > I am sure that you are aware that the typical short wave broadcast
> > transmitter´s
> > audio frequency response curve starts around 50 Hertz and ends quite
> > abruptly
> > at around 4.5 kiloHertz with a very steep slope that is required in
> > order to comply
> > with the channel separation requirements...
> > The studio microphones, audio mixers, master control program
> > amplifiers,
> > fiber optic
> > coders and decoders, STLs etc. are alway easily capable of handling a
> > minimum
> > bandwidth of between 20 and 15,000 Hertz... while the short wave
> > transmitter
> > by its own nature is only cable of responding from about 50 to 4500
> > Hertz... and
> > if you really want to be heard under the most difficult reception
> > conditions, your
> > voice modulation should be restricted to the range between 250 and
> > 3000
> > Hertz or
> > so...
> > 73 and DX
> > YOur friend in Havana
> > Arnie Coro
> > CO2KK
> > Host of Dxers Unlimited radio hobby program
> > Radio Havana Cuba
> >
>
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