[TenTec] Orion Speech Compressors

[Ron Castro]

This is an interesting topic that I deal with regularly in broadcast 
engineering.  The goals are quite a bit different but the way of getting 
there are similar.  You may be surprised to know that many of the top-rated 
FM stations in the country use substantial amounts of clipping of both the 
discrete channel audio and the composite signal fed to the exciter.  This is 
in addition to broadband compression, multi-band spectral compression and 
multi-band spectral limiting.

Distortion-free "fast limiting" can be employed to cause some apparent 
loudness increase, but the real gains don't come until you shave off all the 
useless high peaks and dramatically increase the average power levels which 
include the most important speech formants, such as vowel sounds.  Also, 
clipping causes harmonics that tend to fall into the higher speech ranges 
and add to the power without increasing the peak to average ratio.  Since 
the human ear is more sensitive to sounds in the high voice range (around 
2.4 kHz) the audio tends to stand out, which is exactly what you want to do 
in a pile-up.

That was the secret of the well-known processors of the past such as the DX 
Engineering, the Alpha Vomax and the Datong.

Ron
N6AHA


----- Original Message ----- 
From: "Ken Brown" <ken.d.brown at verizon.net>
To: <tjednacz at ieee.org>; "Discussion of Ten-Tec Equipment" 
<tentec at contesting.com>
Sent: Thursday, February 23, 2006 8:24 PM
Subject: Re: [TenTec] Orion Speech Compressors


> Depends how you define distortion. A typical way to define distortion is
> "output that differs in any way other than a fixed gain or loss compared
> to the input." If a speech processor had no distortion by this
> definition, it would serve no purpose at all. In order for a speech
> processor to be useful, it has to do something to the speech waveform,
> and that something that it does IS distortion by some definitions of
> distortion.
>> There is NO distortion even at higher levels of compression. That is 
>> because
>> the algorithm used in the DSP does the compression correctly. Same in my
>> hearing aids. The compression does not add ANY distortion.
> DE N6KB
>
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