Ir. ( MSc EE) T. Verelst
Using a KB3 program on the Kurzweil PC3 (-76)
synthesizer, I drive a computer with a (large) selection of
rack-effects and FFT-based mastering effect, which in turn
drives a Dual effect Lexicon
effect unit, which gives a Hammond organ simulation a nice
and broadly usable Leslie (rotating speaker/horn) effect.
First, the parameters of the KB3 program are listed
here, using screen-dumps from the latest version of the Soundtower
software, from the Kurzweil
web server, which thus far allowed me to read all the
sounds from my PC3 fitted with Operating
System Update version 2.21, and view the parameters.
I give a description of the Linux based Ladspa/Jack
software effect racks I've used in the below music example made
with the setup:
hammondpc3mx400_2.mp3
44.1kHz sampling frequency, 256 kilo bit per second, stereo mp3, 4
min 31 sec, 8.7 Mega Byte
(Contains pro-audio, not too loud, but mind your speakers and
amps)
(Can be properly used with a upsampling audio player)
including (pretty much) all parameters. If someone would be
interested, they can download the effect rack contents for free
(at request), which is recommendable.
Finally, I present the Lexicon settings for the
Leslie effect, using the Lexicon provided Graphical User Interface
Windows program to interact with the Unit over (Usb) Midi, give
general and specific sound considerations, and sum some of the
experience up in the conclusions.
The main program parameters (this is a special case of the Kurzweil V.A.S.T. sound program parameters, for instance there are no 1..32 layers), including the initial settings of the drawbars:
The effects and the details.
The insert effect is somewhat of an enclosure simulation:
The first and second effect chain, (with details):
The reasoning for using Linux is twofold: I happen to know the
Ladspa plugins, and I appreciate that they're free and do not
render results with a bias I particularly dislike when I combine
many of them, and the Linux OS is much more stable and usually a
lot faster than Windows, and it is natural to run "jackd" the Jack
audio server, with a few tools to manage connections (QJackctl and
Patchage) between the "jack-rack" based effects. Jack reports when
the audio streams have been broken, and I know from years of many
thousands of hours of use that I can run effects until the
processor gets really hot (from the amount of computations), and
still the streams between the processing blocks remain well
behaved, and it is known there are generally no "packet" or buffer
errors, unless Jack reports it. I can run two delays in parallel,
add a inverter block to one of them, by implicit mixing (addition
of the 32 bit floating point audio sample values per channel)
compare those two signal paths, and in almost every case, also
under load, the output sample stream will be exactly zero when the
delays are exactly equal. Most VST and so on programs I do
not know this from, and certainly I have no faith in it the signal
path delay is accurate, fixed, and completely stable.
There are two effects
The connections
The PC3 drives the analog input of a computer Analog to Digital Converter input, which runs at the same sampling clock as the Linux processing: 192 kHz, and has 24 bit resolution. There's no balancing so there's a little bit of hum at the input, but the converter itself is pretty quiet and has a pleasantly neutral character, even though it's input is just on of those tiny 3.5 mm stereo mini jack connectors, found on many motherboards.
The analog inputs L and R for the A effect (in dual effect mode) come from 2 stereo computer motherboard audio outputs, each having been digitally balanced, so the connection is pretty quiet. This construction can easily be used to get analog coupling quality superior to CD quality, at least. It has the advantage that there's so need for a resampling filter to go from 192 kHz to 44.1 (or 48) kHz sampling frequency. Of course a 192hz Lexicon would be great, no doubt.
The TOS / S/PDIF digital signal input of the Lexicon is
still connected to the stable clock source in the Lexicon Omaga
Mixer / Usb-interface, which is connected to the Linux computer
over it's USB connection, which has a driver that recognizes it
automatically. So the Lexicon System settings have been set to
"external digital clock", but "analog stereo input" at the same
time.
Coming out of the Lexicon effects unit (at the bottom of the
above picture from the actual units as used) the digital signal is
connected back to the digital input of the Omega (the top,
standing unit), which makes the digital output signal of the
effect available as a digital signal in the computer (in another
sample frequency domain) where it has been connected with no
processing (except limiting and a little volume lift) to "ffmpeg"
to record the above mp3 sound example file.
The Effect settings
When using a Rotary type of effect, the "Mix 1" isn't a dry/wet
mix but simply a volume control.
The second effect is set to a bit of a standard reverb effect
with all "special" parameters set to low values.
As shown in the introduction, I've made a quick unedited and not
further processed audio demo of the combined setup: hammondpc3mx400_2.mp3.
I played no particular song, except at the end little excerpt of
the well know "green unions" with the "Drive" parameter at a high
setting and a lot of drawbars active.
This setup gives me the only pro-organ sound thus far with a clear, well behaved, full frequency range Leslie effect, that has both clarity and grit, that isn't dangerous when played loud, and that beats all the other effects I've heard thus far, except a few, notable, special cases, where certain effects are specifically "full" or of a certain character. There's degrees of freedom, and I didn't tune a lot of the processing signal chain yet, nor did I much experiment with the KB3 effect chains at all.
It's a pretty good sound, I like more of it, and I suspect
nothing much comes close, which is a nice feeling, even though I'd
want a few more things from organ +Leslie simulation.
Clearly, the Lexicon wants certain signal properties to be there
and balanced, or you'll never ever get close to such sounds as in
the example, it will generally sound screamish, mid-rangy and dull
when connected directly to Kurzweil organ sounds from the ROM
patches, with little exception. So the processing in the computer
is essential, and also the effect chains in the KB3 sound are
essential. Otherwise no cigar for sure.