You are welcome. Yes it's best to use your ear for the aftertouch
adjustment because aftertouch is one of those types of controls that
rely on your ears for feedback as to how much pressure to apply to
create the effect you want. Heavier hands may not need much pressure
while lighter hands will require more pressure and this can be
compensated with more sensitivity/gain. Anyway, it just worked for
me....but make sure you use a modulation that you can clearly hear an
effect with aftertouch like vibrato or pitch...
Bob
El Segundo, CA
--- In AN1x-list@yahoogroups.com, "ecf1001" <ecf1001@...> wrote:
>
> Hello Bob, and thanks for a very informative response!
>
> I suspected the velocity was measured via timed switches but was too
lazy to take it
> completely apart. Thanks for clarifying that. There is hope.
>
> It's interesting that you adjusted the aftertouch sensitivity by ear
without looking at the
> actual MIDI.
>
> Kind regards,
> Alex
>
> --- In AN1x-list@yahoogroups.com, "Bob S." <tttsystems@> wrote:
> >
> > Hello Alex and all
> >
> > I have had my AN1x open to repair and have played with the
internal key mechanism
> dealing with velocity & aftertouch so I will describe what I have
found and maybe you can
> apply the knowledge to help fix this or other problems. Although I
do not have schematics
> or drawings, I am an EE and have put together how it works from
knowledge and
> assumption of how I would have designed it:
> >
> > Keyboard Velocity Control:
> > Velocity is measured by 3 actuator tabs on the middle underside of
each key closing 3
> contact points on an attached circuit board. The electrical contact
is via a rubbery mask
> with attached carbon like pieces contacting etched switch contacts
on a common PC board.
> As the key travels from the up position to the fully depressed
condition, these 3 contacts
> of the key mechanism sequential make contact and close the circuit
paths on the contact
> board. The time is measured between contact closures and a velocity
is calculated. The
> mechanism and design relies upon several things to provide a
consistent velocity from key
> to key:
> > - Mechanical tolerances of the contact mechanism controlled by
controlled length of the
> 3 plastic actuator tabs on the key and the position/flatness of the
contact circuit board.
> The contact circuit board is usually mounted with several dozen
screws (be sure all the
> screw are there and tight) and must be held firm and flat to get
even velocity.
> > - Contact condition and cleanliness. Although the circuit will
probably detect key
> closures fine with normal aging and wear, you many times do not know
how the previous
> owner treated his keyboard. I have found in similar keyboards
things like Pepsi (or was it
> Coke) spilled into a keyboard, corroded contacts (sea air), etc.
causing intermittent
> contacts.
> > - Spring tension of the key which is the force pushing up on the
key while you are
> pushing down. Variances in key pressure will invariably cause the
user to compensate
> and therefore create some variance in the final velocity calculated.
> >
> > Keyboard Aftertouch Control:
> > Aftertouch is determined by pressure on a single resistive strip
that runs along the
> entire keyboard length to an analog circuit that measure the
resistance of the strip.
> Pressing a key down to the end of it's easy travel contacts the key
with the resistive strip
> and press a little further puts additional pressure on the resistive
strip. The analog circuit
> creates a voltage proportional to the pressure and the AN1x takes
that voltage, digitizes it
> and creates an aftertouch value. The analog circuit has 2 tiny
adjustable pots/controls
> mounted on the keyboard circuit board, one for offset and one for
gain. The offset
> controls the initial amount of aftertouch applied to the modulation
path it is set up for.
> This must be matched to the initial crossover point when aftertouch
is first initialed,
> otherwise there will be a jump to the aftertouch modulation instead
of a smooth
> transition. The gain control adjust just that, the sensitivity of
the aftertouch to pressure.
> To get these right, I had to set the AN1x to use aftertouch for say
pitch or vibrato with say
> an 80% effect to the modulation, then iteratively adjust the two
pots while testing the
> result until you like what you get for the pressure you apply.
> >
> > Good Luck
> > Bob
> > El Segundo, CA
> >
> >
> >
> > ----- Original Message -----
> > From: ecf1001
> > To: AN1x-list@yahoogroups.com
> > Sent: Saturday, April 28, 2007 12:20 AM
> > Subject: [AN1x] uneven velocity
> >
> >
> > Hi.
> >
> > I noticed that there are a few keys that produce noticeably
higher velocities than others
> when
> > struck in a fairly consistent way, and I think it's bugging me.
Is there a simple cure for
> this
> > (like cleaning) or does it need to visit its makers? Could dirt
be stuck there and be
> causing all
> > this or is it something more serious? How does the velocity
sensor work, anyway? Is it
> an
> > actual key velocity detector (like on Fatar keyboards) or just a
pressure sensor?
> >
> > Also some of the keys in the vicinty of those with weird
velocity responses smack the
> front
> > plastic lip on the front when played with only moderate force.
Wonder if that's related.
> >
> > Thanks,
> > Alex
>