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[TenTec] Mic. and speech processor questions

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Subject: [TenTec] Mic. and speech processor questions
From: w5yr@swbell.net (George T. Baker)
Date: Tue, 19 Oct 1999 15:01:09 -0500
Bill, you have to be a little careful about lumping all "speech
processors" into the same heap.

I run r-f processing at all times with my Icom IC-765, but not with the
internal processor, which does in fact sound awful. Instead I use a
1970's Comdel processor that generates an SSB signal at 500 KHz, clips
and filters it, and then heterodynes it back down to baseband audio. The
resulting audio is then fed to the 765 mic input. 

Note that this is NOT audio clipping or compression, which is almost
always disastrous on SSB. It is true r-f clipping and filtering, the
result being very low distortion accompanied by a large increase in
average speech power and a significant decrease in the peak-to-average
ratio of the speech waveform. For average speech, voice peaks are
typically 14 db greater than average. As you point out, effective
clipping does make the voice stand out, but this does not have to be as
the result of distortion. 

I run the Comdel such that the average power output while talking is a
factor of four times that with the processor out of the loop. That
amounts to a 6 db average power increase. I can get 12 - 15 db but find
that 6 db is adequate.
A two-tone signal fed into the system emerges as a clean two-tone with or
without processing. That is a very demanding and telling test for any
processing system.

The surprising part is that virtually no one ever spots that I am using
processing and nearly every contact comments on the "clean, sharp audio." 
My voice is naturally rather deep and resonant, so I do not find that
processing does much for me in the way of enhancing my voice for the

The clue here is to start with a good mic (I use the Heil Pro Set with
HC-5 now but for years used the D-104), use a very good r-f processor
adequately but sensibly, and then make sure that the rig is not
overdriven. I monitor all transmissions on all modes with a Monitor Scope
and run frequent two-tone checks. 

Also, one eye on the wattmeter is a good idea. I normally see 10-15 watts
output while speaking without processing and 40-60 watts with processing,
all for 100 watts output keydown or peak. These are typical figures for
most male voices. The power meter also points up the flip side of
processing: much higher average power demand on the rig amplifiers and
power supply which many modern rigs just cannot provide. Processed SSB is
much like RTTY in its duty-cycle requirement. Processing also introduces
problems with background noise in the shack as most of us have observed
with some stations.

Not trying to quarrel with you, Bill, but speech processing gets such a
slam most of the time that I just wanted to report a case where it works
and works very well. It is sadly true that most of the "built-in"
processors found in modern rigs are "marketing after-thoughts" included
just to permit another "feature" to be touted. But the products of
yesterday - the Comdel and the Vomax, in particular - are still around to
enable a station to greatly enhance its effectiveness and retain a clean

72/73, George        AMA 98452          R/C since 1964                 
Amateur Radio W5YR, in the 54th year and it just keeps getting better!  
AutoPOWER Systems, Fairview, TX (30 mi NE Dallas)  Collin County

Bill_Ames@hyperion.com wrote:
> One should never use a speech processor when quality audio is required. If the
> speech processor is doing the very best it can, and is successful, then the
> voice will stand out as louder with more voice power in less bandwidth. The 
> goal
> here is communication under adverse conditions. At all other times the speech
> processor should not be used. The only exception I can think of is when the
> persons normal voice does not drive the rig sufficiently. This could be a 
> result
> of spectral range and power distribution of their voice.
> Bill Ames

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