For the life of me I have never been able to understand why anyone would
want to use "clipping" to process audio. There's much slicker ways, and
have been for years. Fast gain reduction takes care of the problem and does
not generate harmonics as a clipper does. And with a clipper then one must
use a low pass filter to eliminate the harmonics generated which in turn
causes phase shift within the pass band especially as the fundamental
approaches the cut-off frequency.
And yes, a multiband processor is much more effective, and does not generate
IMD or harmonic distortion. And yes, phase coherency is also maintained
between the band, assuming the band pass filtering is done correctly. My
earlier post described a system that I developed and patented some 40 years
ago. Today, only in solid state form and digitally processed, it is still
being used.
73
Bob K4TAX
----- Original Message -----
From: "Tom Rauch" <w8ji@akorn.net>
To: "Joe Word" <joe_word@yahoo.com>; "George W5YR" <w5yr@att.net>
Cc: <tentec@contesting.com>
Sent: Saturday, February 23, 2002 2:37 PM
Subject: Re: [TenTec] Type of Speech Processing in Jupiter/Pegasus?
> I haven't been following this closely, so forgive me if I repeat
> something that has already been said but......
>
> > The r-f clipping and filtering approach which prevents the distortion
> > products from appearing in the output passband is still regarded by
> > most folks as the most effective process to both increase average
> > power and increase articulation.
>
> The most effective processor is a split-band audio processor,
> assuming you can keep the phase constant between channels. It
> is much better than RF processing, which eliminates harmonic
> distortion but not the in-band odd-order IM distortion associated
> with mixing of inband signals with harmonics and harmonics with
> harmonics.
>
> Is that what the Jupiter does???
>
> The 1870's vintage VOMAX was a somewhat frail attempt at this,
> and it would be much better to do it with DSP now. I was actually
> working on a DSP processor which was the equivalent of gain
> compression (AGC), splitting audio into multiple channels with
> individual level controls, "clipping" them with adjustable clipping for
> each channel, converting the clipped waveforms back to sinewaves
> (low pass filtering), and putting them back in phase with adjustable
> levels. But I don't care about SSB enough to finish the work I guess.
>
> If you bandpass-split audio into multiple channels, preventing
> clipping harmonics from falling inside cutoff of each clipper's low-
> pass output filter, you wind up without clipping-generated IMD or
> harmonic distortion no matter how much clipping you use.
>
>
> 73, Tom W8JI
> W8JI@contesting.com
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