[ICOM] Bad TX audio on 775

[sdaitch at mor.ibb.gov]

   I  am  not  familiar with any technique that "compresses" the audio in
   the  manner  you  descibe,  but  there  are/were telephone audio patch
   devices  used in the broadcast industry that would shift the audio up,
   some  250Hz  down the phone line and then shifting the audio back down
   at  the  receive  end,  to give much better low frequency response for
   radio remote broadcasts.  

   This  would  give  almost  250  Hz on the bottom end, making the audio
   sound  better,  with  losing only 250 Hz on the high end, where it was
   far less noticeable.

   Seems to me Comrex was one brand, and they offered several models, one
   using  three  voice  grade  phone  lines to give upways of 8 kHz audio
   bandwidth.    Today,   with  far  more  improved  digital  compression
   techniques, this is no big deal on one voice grade phone line.


   ----- Original Message -----

   From: Art <KY1K at verizon.net>

   Date: Sunday, October 15, 2006 5:06 pm

   Subject: Re: [ICOM] Bad TX audio on 775

   >
   > Compandering is a completely different ball game. To use
   > compandering, the 'normal' 300 to 3000 Hz audio frequencies are
   > 'converted' to different frequencies and then transmitted (over a
   > narrower bandwidth channel). At the other end, the received signal
   > is
   > un-compandered and converted back to it's original 300 to 3KHz
   > communications quality audio. For instance.........
   >
   > These days we have DSP. DSP can take the 300 to 3000 Hz audio
   > input
   > and convert it to 300 to 400 Hz audio. Of course, this audio would
   > not be usable to the human ear. But, the advantage is that the
   > same
   > audio information can now be conveyed by a 100 Hz bandwidth
   > communications channel so LESS NOISE or interference is present.
   > The
   > receiving end takes the 300 to 400 Hz stream and converts it back
   > to
   > 300 to 3 KHz so it can be listened to by a human again.
   >
   > Early compandering efforts in the 70's were a dismal failure, and
   > Motorola (who invested millions in it) finally abandoned all
   > efforts
   > to use it. In those days, they simply didn't have the DSP
   > technology
   > that we have today...so it didn't work. They tried to use analog
   > methods to achieve compandering-you can imagine how crude it
   > was::>
   > However, they still hold the patent(S)::>
   >
   >
   > Regards,
   >
   > Art
   >
   >
   >
   >
   >
   >
   >
   >
   >
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