[Amps] Audio/RF compression

[Manfred Mornhinweg]

Chris, Jim, and all,

in addition to various circuitry that performs audio processing at 
varying levels of versatility, quality, and cost, we should not forget 
the possibility to do it in software. Almost every ham these days has a 
computer in the shack, and usually the computer is up and running during 
all operating. The exception might be mobile stations, emergency 
operation when power is scarce, and so on, but most normal operation is 
done with a computer present. So, audio processing software is an 
attractive option.

One such program is "Voice Shaper", by VE3NEA. Let's see how it fares 
against this wishlist:

> To me it seems like a box with...

Well, it's not a box. Being software, it's invisible, intangible, and 
you can't kick it, but it has a nice window on your PC screen!

> Input gain dial

Yes, it's present, along with a level indicator.

> Output driven dial settable AGC/limiter with fast attack 1 second hold
> and slow decay.
 > 0-10db soft-knee compressor with dialable level and threshold.

Instead of such an AGC/limiter followed by a compressor, this software 
has a soft noise gate, compressor and clipper. Not the same thing, but 
quite usable.

The thresholds and levels are freely adjustable.

Clipping level is adjustable from none to at least 30dB and probably 
more (but that would be useless). Compression is adjustable from none to 
15:1. But the knee seems to be hard.

The noise gate is implemented as a fixed 1:3 expander with variable 
threshold.

It also provides an equalizer, and highpass/lowpass filters. And it 
displays in realtime what's happening with the input and output signal.

It allows you to record your voice and listen to the effects of your 
adjustments in the PC's speakers, and even superimpose noise and QRM to 
hear the improvement in intelligibility, but I doubt the validity of 
that test, due to levels...

Motivated by the related posts over the last few days, this morning I 
downloaded this program and tested it on the air. I'm getting quite 
enthusiastic reports! Clearly better than those I get using the internal 
voice processor of my old radio.

And the cost: Zero, thanks to VE3NEA, if you already have the PC wired 
up to the radio for digimodes, and have a microphone connected to the PC.

Manfred

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