[sdiy] Real piano keyboards: any use?

[cheater cheater]

No idea. I have never built or considered a circuit like you're describing.

What I am talking about is...
Take a normal LPF for a start. A gate goes into that LPF. It's got a
very large time constant (so it's set to a very low 'cutoff' if you
can talk about that with DC signals). When the gate triggers, the
input signal abruptly changes state from say 0 to +5V. The LPF
slew-limits that, and therefore you get a raising slope. Once the
output = input (so, the slope is raised), a special trigger feeds back
to where the gate came from, and turns it off. Then the gate turns off
to 0V. So again the output of the LPF goes from +5V to 0V in a
slew-limited fashion, which gives you the release stage.

Right now you only have one knob that controls the attack and release
time at the same time. This means the LPF is symmetric, because it
'works the same way in both directions', for signals with a positive
and negative slope. A more sophisticated filter can have a different
time constant for signals with a positive, and for signals with a
negative slope.

Cheers
Damian

On Thu, Jan 29, 2009 at 11:31 PM, David G. Dixon
<dixon at interchange.ubc.ca> wrote:
> Hey, D.:
>
> I tried searching for asymmetric LPFs on the web, but came up empty-handed.
> I can also find nothing about it in Horowitz and Hill.  So, let me see if I
> understand you correctly:
>
> My vision of a simple AR is two diodes in opposite directions feeding two
> (variable, or just differently valued) resistors which then come together
> across a single (typically fairly large) cap to ground.  Obviously, if the
> voltage input has different polarities it will be shunted across the
> different diodes, thus rendering the filtering asymmetric.
>
> Using active rectifiers rather than just bare diodes would eliminate the
> diode voltage drop and its associated crossover distortion, which would make
> the device useful for filtering actual signals rather than just gate inputs.
>
> Does this more or less correspond with what you are talking about?
>
> Cheers,
> Dave
>
> David G. Dixon
> Professor
> Department of Materials Engineering
> University of British Columbia
> 309-6350 Stores Road
> Vancouver, B.C. V6T 1Z4
> Canada
>
> Tel 1-604-822-3679
> Fax 1-604-822-3619
>
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>
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>> -----Original Message-----
>> From: synth-diy-bounces at dropmix.xs4all.nl [mailto:synth-diy-
>> bounces at dropmix.xs4all.nl] On Behalf Of cheater cheater
>> Sent: Thursday, January 29, 2009 1:34 PM
>> To: synth-diy at dropmix.xs4all.nl
>> Subject: Re: [sdiy] Real piano keyboards: any use?
>>
>> No, if you feed an asymmetric LPF something other than a gate signal
>> you won't get an AR signal out of it.
>>
>> Think of sidechains in compressors. The loudness analyzers are
>> (usually) asymmetric LPFs fed the rectified signal you put into the
>> sidechain.
>>
>> Cheers
>> D.
>>
>> On Thu, Jan 29, 2009 at 9:09 PM, David G. Dixon
>> <dixon at interchange.ubc.ca> wrote:
>> > Ah.  I get it.  It's an AR.
>> >
>> > David G. Dixon
>> > Professor
>> > Department of Materials Engineering
>> > University of British Columbia
>> > 309-6350 Stores Road
>> > Vancouver, B.C. V6T 1Z4
>> > Canada
>> >
>> > Tel 1-604-822-3679
>> > Fax 1-604-822-3619
>> >
>> > "PERFECTA FINGAMUS SERVIAT NATURA"
>> >
>> > The information in this email and in any attachments is confidential and
>> > intended solely for the attention and use of the named addressee(s).  It
>> > must not be disclosed to any person without the writer's authority.  If
>> you
>> > are not the intended recipient, or a person responsible for delivering
>> it to
>> > the intended recipient, you are not authorized to and must not disclose,
>> > copy, distribute, or retain this message or any part of it.
>> >> -----Original Message-----
>> >> From: synth-diy-bounces at dropmix.xs4all.nl [mailto:synth-diy-
>> >> bounces at dropmix.xs4all.nl] On Behalf Of cheater cheater
>> >> Sent: Thursday, January 29, 2009 12:27 PM
>> >> To: synth-diy at dropmix.xs4all.nl
>> >> Subject: Re: [sdiy] Real piano keyboards: any use?
>> >>
>> >> An AR is a non-symmetric LPF that you put a gate into and get an AR
>> >> envelope out of.[1]
>> >>
>> >> An assymmetric LPF is an LPF where the 'slew rate'*is set separately
>> >> for rising and falling signals.
>> >>
>> >> *(actually: time coefficients)
>> >>
>> >> [1] That's why different gate designs make your synth sound
>> >> differently. It's all in the transient!
>> >>
>> >> Cheers
>> >> D.
>> >>
>> >> On Thu, Jan 29, 2009 at 8:15 PM, David G. Dixon
>> >> <dixon at interchange.ubc.ca> wrote:
>> >> >> It does indeed!
>> >> >> I think the best way to achieve this kind of control is to have a
>> >> >> continuous optic distance sensor. This can give you acceleration
>> >> >> output and position output.
>> >> >> Imagine having a synth style keyboard with the position going to the
>> >> >> volume of the voice, and the speed going (through a non-symmetric
>> LPF
>> >> >> with a long release) to the volume of the suboctave. This would be a
>> >> >> great lead/pad patch.
>> >> >
>> >> > Did you mean "non-symmetric AR" as in fast attack, long release?
>> What
>> >> is a
>> >> > non-symmetric LPF?
>> >> >
>> >> >
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