The Eat at Joe's Kawai K5000 Message Board Digest
Tricks with Additive Synthesis and the Formant Filter
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Those nonlinear rates and levels
Friday, 27-Feb-98 03:48:44
130.67.0.118 writes:
At one time I believe I saw one of you - maybe it was Kenji - post information
about the nonlinear nature of harmonics levels and how you had taken this into
account in making a sawtooth wave. I cannot find that in the digest, so maybe
the poster could point me to the right place or repeat the explanation, please?
The thing is, the envelopes we get from books or PC sound tools need to be
translated into K5000 terms, and for this purpose we need to know the precise
nature of the rates and levels. The rates of the harmonic envelopes appear
to be logarithmic. For a given level, the time needed to reach it seems to be
proportional to 2^(-Rate/8). (Anyone know this for sure?) However, the level
also needs to be part of this formula for the time, and it is obviously nonlinear.
That's why I ask for that formula posted previously.
Tore
tl001@online.no
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Re: Those nonlinear rates and levels
Friday, 27-Feb-98 04:36:09
194.172.230.108 writes:
Hi Tore!
It's here: (Let's see if the following becomes a link; otherwise, you will find
it "by hand".) Things that Should be in the Manual (Details!)
0.75 dB per step means, as formula:
amplitude = max_amplitude * 2^((level_value-127)/8)
Or:
level_value = 127 + 8 * log2(amplitude/max_amplitude)
To create a sawtooth wave, the amplitude spectrum must be inversely proportional
to the harmonic number, that is:
level_value = 127 - 8 * log2(harmonic_number)
For those who are missing the base-2 logarithm on their pocket calculator - use this:
log2(...) = ln(...) / ln(2)
Have fun with your additive sawtooth!
Jens Groh
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Re: Re: Those nonlinear rates and levels
Friday, 27-Feb-98 08:42:41
194.172.230.108 writes:
(Sorry Tore, I should have read your post twice before answering - just a
"levels" discussion is in that digest section, not the "sawtooth" discussion.)
Jens Groh
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Re: Re: Those nonlinear rates and levels
Friday, 27-Feb-98 08:56:38
130.67.1.157 writes:
Thank you, this was a very clear presentation. Unfortunately, these formulas
don't seem to explain how the time varies with the level, when keeping the rate
constant - there appears to be an inverse logarithmic relationship here. I'll
do some more experiments before I quote numbers.
Tore
tl001@online.no
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Re: Re: Re: Those nonlinear rates and levels
Friday, 27-Feb-98 10:23:17
194.172.230.108 writes:
Interesting! - I have made the same experience with the rate/time behaviour. For
the rate influence, I can confirm your 2^(-Rate/8) formula. What may be the
algorithm that generates the level ramp? (Now, that's "reverse engineering",
isn't it? ;-)
I'm planning to publish a patch of mine here (Check out soon ADDpegio) that uses
precice rate values to create an arpeggio just from the harmonics. It's fun!
Ha det bra! (Nej Tore, jeg snakker ikke norsk!)
Jens Groh
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Re: Re: Re: Re: Those nonlinear rates and levels
Sunday, 01-Mar-98 07:45:40
130.67.65.183 writes:
One thing that is certain about the time needed to change a level is that this
movement is accelerated. And it appears that the acceleration is greater for low
levels than for higher ones. Going from level 0 to 10 in the Harmonics Envelopes
takes around 10 secs at a rate of 42, going from 50 to 60 takes 16 secs. The
differential equation for this movement ought to be something like l'' = a0 - kl,
where l'' is the second derivative of the level, a0 the initial acceleration, and k is
a constant. a0 would vary depending on where we begin the movement, and going
downward would give us a plus sign in front of kl. My calculus is VERY
rusty, so correct me if I am wrong.
Whatever is the solution of this equation, I don't think it will be practicable
to calculate such time functions whenever one wants to e.g. change a level while
keeping the time constant. It will be simpler to make tables where one can see at
a glance how to adjust the rate in the different cases. Hopefully, Kawai will
come forward with some explanation for why the K5000 was designed this way and
maybe tell us some simple ways of doing things.
Tore
tl001@online.no
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Using the FF as an Envelope Generator, "Starfall" Patch
Saturday, 28-Feb-98 11:52:58
199.86.33.67 writes:
The preset "Chimera" (D20 on the K5kR) has a pretty clever technique in it, which
uses the FF as an envelope. The FF envelope moves the FF across the
harmonics slowly, over a long distance. The FF is shaped like the envelope of an
oscillating bell, so as it passes over each harmonic (only a few are selected)
the harmonic rings like a bell. This gets a lot of notes out of a single ADD,
although they're all sines.
I'm sending in a patch, "Starfall", which uses this technique.
(It sounds like Jens may have come up with this as well with the "ADDpegio"
patch he's sending.)
leiter@skypoint.com
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Re: Using the FF as an Envelope Generator, "Starfall" Patch
Monday, 02-Mar-98 04:07:58
194.172.230.108 writes:
Hi all!
QUOTE
(It sounds like Jens may have come up with this as well with the "ADDpegio" patch
he's sending.)
UNQUOTE
No, the Formant Filter method is new to me.
My patch creates an arpeggio with DHEnvelopes only and uses the FF just to
"switch" between variations of it when you turn the FF BIAS knob.
But it's a good idea! Perhaps you can even make it cyclic like in Kenji's
"Shimmer" patch.
Jens Groh
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Re: Re: Using the FF as an Envelope Generator, "Starfall" Patch
Wednesday, 04-Mar-98 05:44:00
12.68.132.238 writes:
There is another technique which is related and can be found under add source 1
under A22 called Creaturz; FF has 1 band at 127, all others at 0, FF is not
in envelope mode but LFO mode and its shape is random. This makes really cool
"bell?" like sounds. Chaning FF bias or LFO speed has interesting results. I
really enjoy this board!!!
Peter Favant
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