Emu XL-7 & MP-7 User's Group

Huge, huge thanks man!

rEalm





"Aaron Eppolito" <synthesis77@...>
03/25/2004 12:20 PM
Please respond to xl7

 
        To:     xl7@yahoogroups.com
        cc: 
        Subject:        Re: [xl7] Re: How do I make my bass line "drop"??


--- erik_magrini@... wrote:
> Do you think you could explain your thought process behind using
> each one of those modulation options?

Sure.  I'm doing this off the top of my head so I apologize if I'm not
right with something here.

MIDI N   -> Quantize  +75%
--------------------------
Quantize divides the input signal into ~16 parts at 98% input.  For
example, given these inputs, you'll get this output:
0-7 in   - 0 out
8-15 in  - 8 out
16-31 in - 16 out
etc.

Since we wanted (or at least I wanted) an octave drop, I set it to 75%
(16 steps times 75% = 12 steps).  I'm actually oversimplifying here
(it's actually 17 steps, and you want 13, but it rounds up...) but
trial and error gives the right value.  Hook it up to something and
count the steps.

Quantize -> Fine Pitch -6%
Quantize -> Pitch     -50%
--------------------------
Now that we have a stair step input signal in response to the
continuous input, we can route that to pitch.  Normally to get an
octave on the XL-7, you would route the controller to Pitch at 38% and
FinePitch at 6%.  Yeah, I know, why the previous engineers didn't
choose a round number (like 50% to Pitch = one octave) I don't know,
but that's the way it goes.  Anyway, 50% here gives us an octave
because we already multiplied the input by 75% (hey, whatdya know, 75%
* 50% = ~%38) so we route the quantize to Pitch and Fine Pitch (now
that I think of it, that 6% probably isn't right in this context).

MIDI N   -> AmpVol    -30%
MIDI N   -> FiltFreq -100%
--------------------------
These two cords simply drop off the volume and Fc as the drop
progresses.  This is just to model how a bass guitar loses volume and
more so brightness when you loose clean contact with a fret.  (fingers
absorb high frequencies much more than frets do).

Now for the hard stuff:
I just realized I wrote this up wrong.  The following cords are what I
had in my XL-7, the ones I posted in the previous post are not.
Quantize -> Gain4X   +100%
Quantize -> Lag0In   +100%
Lag0     -> Gain4X   -100%
Gain4X   -> Abs      +100%
Abs      -> FiltFreq +100%


So anyway, here's a breakdown of what this chunk of cords does.
Quantize -> Gain4X   +100%
Quantize -> Lag0In   +100%
Lag0     -> Gain4X   -100%
--------------------------
This creates an approximate differentiator.  For those who didn't do so
hot in Calculus (like me; calc kicked my ass) a differentiator creates
a signal that is proportionate to how quick the input signal changes. 
For a real world example, Acceleration is the derivative of Speed, i.e.
acceleration is big when you start increasing your speed quickly.

By subtracting a lagged quantity from the original quantity, you get an
approximation of how quick you're changing.  In our case, since we have
a stairstep input (by virtue of the quantizer) each step has a huge
acceleration giving us an impulse at each step.  Differentiators are
*very* useful in synths.  Try using one to increase chorus when
changing pitch to get a symphonic type sound.

Gain4X   -> Abs      +100%
--------------------------
Since the differentiator produces signed output (positive when the
steps go up, negative when the steps go down) I'm running it through an
absolute value so that no matter whether you're sliding up the
fretboard or down the fretboard, the pulse is positive.

Abs      -> FiltFreq +100%
--------------------------
And finally, do something with the differentiated signal.  The above
cord "pokes" Fc at each fret.  It's not terribly exciting.  Better
would be to copy all these cords to a duplicate layer with a buzzy
sound and target AmpVol to increase the level.

Okay, that's my synth lesson for the day.  Your assignment?  Go program
something!  Enjoy the fact that your ROMpler is more of a synth than
some VAs!  =)

-Aaron

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