Sigi as you are using VST plugins have you
tried the Waves L3 Multimaximizer? It is hard to make it sound
bad and it certainly increases talk power with minimal
distortion, it never overshoots.
the nice thing when using all in software (sdr) you can do
things with compression, limiter, etc etc ... that you can NOT
do with analogue circuits
your "rf clipper" may produce a more boosted signal ... but i
guess when all is made in software you can be a bit better
the sdr has the audio in a chain (buffer) and you can have a
look forward agc ... limit every word to the maximum without
overshooting or harmonics produced
and with a monitor receiver on the output of your amp you can
add predistortion ... result is an even cleaner (but more
no way to do that with conventional circuits
you could try to combine your rf clipper with the processor
in sdrc (but do not crank it up tooo much) ... i do a simlar
thingy with my mixing software (voicemeeter potatoe) with some
vst plugins added in the chain ... first the plugins do a tiny
bit of compression and limits the peaks not to overdrive the
sdrc input ... and a bit of processing of the sdrc is added
afterwards ... the result is a well boosted signal with no
splatter (pay also attention not to produce intermod
distortion on the final amp or driving stages!!)
simon you have the equalizer ... what if each filter in the
eq would have its own processor and limiter?? is that what you
mean with half octave filters (and boosting those) ?!?!?
Am 31.08.2021 um 12:01 schrieb MikeC:
Interesting article. I did experiment
further with the processor settings and compared the result
with an analogue speech processor that was part of a ssb rig
I designed about 20 years ago. This processor uses variable
rf log clipping of an ssb signal (at 10.7MHz) followed by
another ssb filter. The audio is pre-processed by a syllabic
compressor (a vogad). The clipping is done with two stages
of log amplifiers. In the original design the resulting ssb
was converted to the required frequency but I had already
added a demodulator back down to audio for something else so
here the output is audio. As the article points outs, non dc
baseband clipping avoids the serious harmonic distortion
that baseband clipping induces at all but very light
clipping because the harmonics multiply outside the
passband. There are still intermodulation products that
eventually limit performance.
Of course this processor is very
component hungry by today’s standards and I happened to have
it on the shelf. As the article also points out, the the
same result can be achieved in dsp by other means that could
not be realised in practice by analogue circuits.
I feed the audio output at line level
into the pc and have the SDRC processor turned off. The
audio processor bandwidth is from about 200Hz to 2.4kHz,
determined almost entirely by the analogue ssb filters.
I think that overshoot is a slightly
different, but related problem. Interestingly though I had a
look at this processor’s performance by putting test sine
and square-waves frequencies into it and looking at the
audio output on a scope. Probably by more luck than
judgement, the overshoot is a few percent unless the
processing is set ridiculously high. I suspect that a
fortuitous combination of filters and time constants, plus
the relatively narrow bandwidth requirement helps.
I have not checked for overshoot on the
rf output from the Limesdr that eventually generates the
signal for transmission.
My metering indicates that the average to
peak power ratio has increased significantly and, although
this is pretty unscientific, the “hf pileup breaking index”
is markedly improved.
Nothing can be all things to all men (or
women). Everything is a compromise of requirements,
performance, complexity, time and cost.
Mail for Windows
I use a single band RMS compressor
followed by a very-well designed limiter which avoids
overshoot. I’ve tried multi-band compressors but not
achieved much benefit. When I get into my main winter
project I may look at this again, having a compressor
instance for each octave or half-octave.
For winter I want to finally play with my
Hermes-Lite 2, with my main amplifier I’ll have ~350 watts
so will want to boost the audio.
Simon Brown, G4ELI
- 73 -