20 Jul
2009
20 Jul
'09
1:11 a.m.
Just a quick update on the wah research.
A friend owns a Dunlop "Jimi Hendrix Wah", which says it is the "Original
Thomas Design", by which I assume they mean to claim it's the same design as the
Thomas Organ Wah, formerly Vox.
This website's describes the frequency response as a lowpass with a resonant peak:
http://www.geofex.com/Article_Folders/wahpedl/wahped.htm
So here is what JAPA says it does (and I believe JAPA more than some random website):
When fully closed, it's a bandpass, with a VERY high Q!
http://restivo.org/misc/lowend-jimi.png
But, wait, when I open it up, suddenly it becomes more like a highpass, but with a lot of
resonance:
http://restivo.org/misc/midrange-jimi.png
When it's fully opened, it's definitely a highpass, but with a helluva peak:
http://restivo.org/misc/high-jimi.png
So, not only is the opposite of what that article says, but it's also kind of
non-linear. I'll poke around the various LADSPA plugins and see if I can find
something nearly like this.
Another guitar-player friend has a different wah (IIRC, either a "Cry Baby", or
a Morley), and I'll see if I can run his through this and see what it comes up looking
like.
-ken
20 Jul
20 Jul
2:32 a.m.
On Sun, Jul 19, 2009 at 8:10 PM, Ken Restivo<ken(a)restivo.org> wrote:
Just a quick update on the wah research.
A friend owns a Dunlop "Jimi Hendrix Wah", which says it is the "Original
Thomas Design", by which I assume they mean to claim it's the same design as the
Thomas Organ Wah, formerly Vox.
This website's describes the frequency response as a lowpass with a resonant peak:
http://www.geofex.com/Article_Folders/wahpedl/wahped.htm
So here is what JAPA says it does (and I believe JAPA more than some random website):
When fully closed, it's a bandpass, with a VERY high Q!
http://restivo.org/misc/lowend-jimi.png
But, wait, when I open it up, suddenly it becomes more like a highpass, but with a lot of
resonance:
http://restivo.org/misc/midrange-jimi.png
When it's fully opened, it's definitely a highpass, but with a helluva peak:
http://restivo.org/misc/high-jimi.png
So, not only is the opposite of what that article says, but it's also kind of
non-linear. I'll poke around the various LADSPA plugins and see if I can find
something nearly like this.
Another guitar-player friend has a different wah (IIRC, either a "Cry Baby", or
a Morley), and I'll see if I can run his through this and see what it comes up looking
like.
-ken
_______________________________________________
Linux-audio-user mailing list
Linux-audio-user(a)lists.linuxaudio.org
http://lists.linuxaudio.org/mailman/listinfo/linux-audio-user
Cool. Nice to see some good open source DSP design in process. Is your
goal to make something like a wah with a combination of LADSPA plugins
or would you also consider making a new plugin emulating this
behavior? It may be worth considering trying to build something in
puredata or csound, given that they have much more fine grained
control for building customized processing chains than could be done
in a single instance of jack-rack.
I think the best way to mimic the wah behavior will probably be to
manipulate the Q and center frequency based on a pair of table
lookups, or additionally/alternatively you could have a pair of
filters and crossfade between them based on your virtual pedal
position.
3:25 a.m.
On Sun, Jul 19, 2009 at 09:32:21PM -0700, Justin Smith wrote:
On Sun, Jul 19, 2009 at 8:10 PM, Ken
Restivo<ken(a)restivo.org> wrote:
I'm either going to find a LADSPA plugin which does this, or hack something together
in JACK-RACK or via some custom C using existing plugins.
I haven't the maths skills to write any serious DSP in C, and probably not in PD or
Csound either. Whatever I end up with will have to be in C, however, and efficient too,
so it can run on a netbook along with many other synths and plugins.
Just a quick update on the wah research.
A friend owns a Dunlop "Jimi Hendrix Wah", which says it is the "Original
Thomas Design", by which I assume they mean to claim it's the same design as the
Thomas Organ Wah, formerly Vox.
This website's describes the frequency response as a lowpass with a resonant peak:
http://www.geofex.com/Article_Folders/wahpedl/wahped.htm
So here is what JAPA says it does (and I believe JAPA more than some random website):
When fully closed, it's a bandpass, with a VERY high Q!
http://restivo.org/misc/lowend-jimi.png
But, wait, when I open it up, suddenly it becomes more like a highpass, but with a lot of
resonance:
http://restivo.org/misc/midrange-jimi.png
When it's fully opened, it's definitely a highpass, but with a helluva peak:
http://restivo.org/misc/high-jimi.png
So, not only is the opposite of what that article says, but it's also kind of
non-linear. I'll poke around the various LADSPA plugins and see if I can find
something nearly like this.
Another guitar-player friend has a different wah (IIRC, either a "Cry Baby", or
a Morley), and I'll see if I can run his through this and see what it comes up looking
like.
Cool. Nice to see some good open source DSP design in process. Is your
goal to make something like a wah with a combination of LADSPA plugins
or would you also consider making a new plugin emulating this
behavior? It may be worth considering trying to build something in
puredata or csound, given that they have much more fine grained
control for building customized processing chains than could be done
in a single instance of jack-rack.
I think the best way to mimic the wah behavior will
probably be to
manipulate the Q and center frequency based on a pair of table
lookups, or additionally/alternatively you could have a pair of
filters and crossfade betwengn them based on your virtual pedal
position.
Tonight I tried every LADSPA bandpass filter I could find, and none came even close
AFAICT. Comparing its shape to those of other LADSPA plugins indicates to me that the
"Thomas Organ" wah circuit isn't a band-pass after all, just a high-pass
with a VERY high Q. So, yeah, I might be able to get pretty close with one ofthe existing
LADSPA HPF's and varying the Q, as you suggested.
-ken
3:33 a.m.
On Sun, Jul 19, 2009 at 10:24 PM, Ken Restivo<ken(a)restivo.org> wrote:
On Sun, Jul 19, 2009 at 09:32:21PM -0700, Justin Smith
wrote:
Just to clarify, the pd or csound solution would only have to have
premade filters in it, plus some parameter routing, the issue with
jack-rack is that you cannot tie parameters to one another in
jack-rack itself (and as far as I know you cannot even have parallel
signal paths), and any external solution you hack together is going to
be less efficient and more fragile than pd, csound, or the like. When
you say whatever you make would have to be written in c I hope you
understand that pd and csound are written and c and will have less
overhead than jack-rack plus whatever midi preprocessing and shell
scripting you need for the alternative approach (though I will not
argue the fact that coding the whole thing in c would be even more
efficient, but also more time consuming and error prone than a
dedicated DSP language).
Suddenly it occurs to me that maybe your goal is to get me so
opinionated about the right way to do this that I just do it for you
myself :)
On Sun, Jul 19, 2009 at 8:10 PM, Ken
Restivo<ken(a)restivo.org> wrote:
I'm either going to find a LADSPA plugin which does this, or hack something together
in JACK-RACK or via some custom C using existing plugins.
I haven't the maths skills to write any serious DSP in C, and probably not in PD or
Csound either. Whatever I end up with will have to be in C, however, and efficient too,
so it can run on a netbook along with many other synths and plugins.
Just a quick update on the wah research.
A friend owns a Dunlop "Jimi Hendrix Wah", which says it is the "Original
Thomas Design", by which I assume they mean to claim it's the same design as the
Thomas Organ Wah, formerly Vox.
This website's describes the frequency response as a lowpass with a resonant peak:
http://www.geofex.com/Article_Folders/wahpedl/wahped.htm
So here is what JAPA says it does (and I believe JAPA more than some random website):
When fully closed, it's a bandpass, with a VERY high Q!
http://restivo.org/misc/lowend-jimi.png
But, wait, when I open it up, suddenly it becomes more like a highpass, but with a lot of
resonance:
http://restivo.org/misc/midrange-jimi.png
When it's fully opened, it's definitely a highpass, but with a helluva peak:
http://restivo.org/misc/high-jimi.png
So, not only is the opposite of what that article says, but it's also kind of
non-linear. I'll poke around the various LADSPA plugins and see if I can find
something nearly like this.
Another guitar-player friend has a different wah (IIRC, either a "Cry Baby", or
a Morley), and I'll see if I can run his through this and see what it comes up looking
like.
Cool. Nice to see some good open source DSP design in process. Is your
goal to make something like a wah with a combination of LADSPA plugins
or would you also consider making a new plugin emulating this
behavior? It may be worth considering trying to build something in
puredata or csound, given that they have much more fine grained
control for building customized processing chains than could be done
in a single instance of jack-rack.
I think the best way to mimic the wah behavior
will probably be to
manipulate the Q and center frequency based on a pair of table
lookups, or additionally/alternatively you could have a pair of
filters and crossfade betwengn them based on your virtual pedal
position.
Tonight I tried every LADSPA bandpass filter I could find, and none came even close
AFAICT. Comparing its shape to those of other LADSPA plugins indicates to me that the
"Thomas Organ" wah circuit isn't a band-pass after all, just a high-pass
with a VERY high Q. So, yeah, I might be able to get pretty close with one ofthe existing
LADSPA HPF's and varying the Q, as you suggested.
-ken
3:37 a.m.
On Sun, Jul 19, 2009 at 10:33 PM, Justin Smith<noisesmith(a)gmail.com> wrote:
On Sun, Jul 19, 2009 at 10:24 PM, Ken
Restivo<ken(a)restivo.org> wrote:
Never mind, I replied too soon, reading what you wrote more carefully,
I think what I said was mostly moot.
On Sun, Jul 19, 2009 at 09:32:21PM -0700, Justin
Smith wrote:
Just to clarify, the pd or csound solution would only have to have
premade filters in it, plus some parameter routing, the issue with
jack-rack is that you cannot tie parameters to one another in
jack-rack itself (and as far as I know you cannot even have parallel
signal paths), and any external solution you hack together is going to
be less efficient and more fragile than pd, csound, or the like. When
you say whatever you make would have to be written in c I hope you
understand that pd and csound are written and c and will have less
overhead than jack-rack plus whatever midi preprocessing and shell
scripting you need for the alternative approach (though I will not
argue the fact that coding the whole thing in c would be even more
efficient, but also more time consuming and error prone than a
dedicated DSP language).
Suddenly it occurs to me that maybe your goal is to get me so
opinionated about the right way to do this that I just do it for you
myself :)
On Sun, Jul 19, 2009 at 8:10 PM, Ken
Restivo<ken(a)restivo.org> wrote:
I'm either going to find a LADSPA plugin which does this, or hack something together
in JACK-RACK or via some custom C using existing plugins.
I haven't the maths skills to write any serious DSP in C, and probably not in PD or
Csound either. Whatever I end up with will have to be in C, however, and efficient too,
so it can run on a netbook along with many other synths and plugins.
Just a quick update on the wah research.
A friend owns a Dunlop "Jimi Hendrix Wah", which says it is the "Original
Thomas Design", by which I assume they mean to claim it's the same design as the
Thomas Organ Wah, formerly Vox.
This website's describes the frequency response as a lowpass with a resonant peak:
http://www.geofex.com/Article_Folders/wahpedl/wahped.htm
So here is what JAPA says it does (and I believe JAPA more than some random website):
When fully closed, it's a bandpass, with a VERY high Q!
http://restivo.org/misc/lowend-jimi.png
But, wait, when I open it up, suddenly it becomes more like a highpass, but with a lot of
resonance:
http://restivo.org/misc/midrange-jimi.png
When it's fully opened, it's definitely a highpass, but with a helluva peak:
http://restivo.org/misc/high-jimi.png
So, not only is the opposite of what that article says, but it's also kind of
non-linear. I'll poke around the various LADSPA plugins and see if I can find
something nearly like this.
Another guitar-player friend has a different wah (IIRC, either a "Cry Baby", or
a Morley), and I'll see if I can run his through this and see what it comes up looking
like.
Cool. Nice to see some good open source DSP design in process. Is your
goal to make something like a wah with a combination of LADSPA plugins
or would you also consider making a new plugin emulating this
behavior? It may be worth considering trying to build something in
puredata or csound, given that they have much more fine grained
control for building customized processing chains than could be done
in a single instance of jack-rack.
I think the best way to mimic the wah behavior
will probably be to
manipulate the Q and center frequency based on a pair of table
lookups, or additionally/alternatively you could have a pair of
filters and crossfade betwengn them based on your virtual pedal
position.
Tonight I tried every LADSPA bandpass filter I could find, and none came even close
AFAICT. Comparing its shape to those of other LADSPA plugins indicates to me that the
"Thomas Organ" wah circuit isn't a band-pass after all, just a high-pass
with a VERY high Q. So, yeah, I might be able to get pretty close with one ofthe existing
LADSPA HPF's and varying the Q, as you suggested.
-ken
4:11 a.m.
Ken!
I've got a Cry Baby here. If you'd tell me what you need, I might get you
some recordings.
Kindest regards
Julien
--------
Music was my first love and it will be my last (John Miles)
======== FIND MY WEB-PROJECT AT: ========
http://ltsb.sourceforge.net
the Linux TextBased Studio guide
======= AND MY PERSONAL PAGES AT: =======
http://www.juliencoder.de
5:45 a.m.
No, I meant what would you need to analyse in JAPA?
--------
Music was my first love and it will be my last (John Miles)
======== FIND MY WEB-PROJECT AT: ========
http://ltsb.sourceforge.net
the Linux TextBased Studio guide
======= AND MY PERSONAL PAGES AT: =======
http://www.juliencoder.de
7:57 a.m.
On Sun, Jul 19, 2009 at 08:10:47PM -0700, Ken Restivo wrote:
Just a quick update on the wah research.
A friend owns a Dunlop "Jimi Hendrix Wah", which says it is the "Original
Thomas Design", by which I assume they mean to claim it's the same design as the
Thomas Organ Wah, formerly Vox.
This website's describes the frequency response as a lowpass with a resonant peak:
http://www.geofex.com/Article_Folders/wahpedl/wahped.htm
So here is what JAPA says it does (and I believe JAPA more than some random website):
When fully closed, it's a bandpass, with a VERY high Q!
http://restivo.org/misc/lowend-jimi.png
But, wait, when I open it up, suddenly it becomes more like a highpass, but with a lot of
resonance:
http://restivo.org/misc/midrange-jimi.png
When it's fully opened, it's definitely a highpass, but with a helluva peak:
http://restivo.org/misc/high-jimi.png
So, not only is the opposite of what that article says, but it's also kind of
non-linear. I'll poke around the various LADSPA plugins and see if I can find
something nearly like this.
Another guitar-player friend has a different wah (IIRC, either a "Cry Baby", or
a Morley), and I'll see if I can run his through this and see what it comes up looking
like.
AFAICS this is a resonant (which is not the same as bandpass) filter.
If the response near Fs/2 bcomes flat, that does not mean it is a
highpass.
Remember that any digital filter is 'mirrored' to the other side
of Fs/2. Also the magnitude of the response must be continuous or
zero at all points (for finite order).
The result of all this is that at Fs/2 the response must be either
zero or have a zero derivative, i.e. be horizontal.
In a high order filter you can make the 'roundoff' region near
Fs/2 very small, but it's always there, unless the response is
zero at that frequency.
You can probably get this type of response using the MOOG VCF
by taking the output at a different point in the algorithm.
The MOOG VCF is 4th order, this is overkill as the analog
circuit is very likely to be just 2nd order.
Ciao,
--
FA
Io lo dico sempre: l'Italia è troppo stretta e lunga.
10:12 p.m.
On Mon, Jul 20, 2009 at 11:51:07AM +0200, Fons Adriaensen wrote:
On Sun, Jul 19, 2009 at 08:10:47PM -0700, Ken Restivo
wrote:
Thanks. Alas, that seems like a very concise explanation, but I don't have the
mathematical background to implement that.
If someone feels like modifying the Moog VCF to make it a Vox/Thomas Wah, I'd be
eternally grateful. But it's pretty clear I don't have the skills to take this
over the finish line.
-ken
Just a quick update on the wah research.
A friend owns a Dunlop "Jimi Hendrix Wah", which says it is the "Original
Thomas Design", by which I assume they mean to claim it's the same design as the
Thomas Organ Wah, formerly Vox.
This website's describes the frequency response as a lowpass with a resonant peak:
http://www.geofex.com/Article_Folders/wahpedl/wahped.htm
So here is what JAPA says it does (and I believe JAPA more than some random website):
When fully closed, it's a bandpass, with a VERY high Q!
http://restivo.org/misc/lowend-jimi.png
But, wait, when I open it up, suddenly it becomes more like a highpass, but with a lot of
resonance:
http://restivo.org/misc/midrange-jimi.png
When it's fully opened, it's definitely a highpass, but with a helluva peak:
http://restivo.org/misc/high-jimi.png
So, not only is the opposite of what that article says, but it's also kind of
non-linear. I'll poke around the various LADSPA plugins and see if I can find
something nearly like this.
Another guitar-player friend has a different wah (IIRC, either a "Cry Baby", or
a Morley), and I'll see if I can run his through this and see what it comes up looking
like.
AFAICS this is a resonant (which is not the same as bandpass) filter.
If the response near Fs/2 bcomes flat, that does not mean it is a
highpass.
Remember that any digital filter is 'mirrored' to the other side
of Fs/2. Also the magnitude of the response must be continuous or
zero at all points (for finite order).
The result of all this is that at Fs/2 the response must be either
zero or have a zero derivative, i.e. be horizontal.
In a high order filter you can make the 'roundoff' region near
Fs/2 very small, but it's always there, unless the response is
zero at that frequency.
You can probably get this type of response using the MOOG VCF
by taking the output at a different point in the algorithm.
The MOOG VCF is 4th order, this is overkill as the analog
circuit is very likely to be just 2nd order.
21 Jul
21 Jul
11:44 a.m.
On Mon, Jul 20, 2009 at 05:11:50PM -0700, Ken Restivo wrote:
Thanks. Alas, that seems like a very concise
explanation, but I don't have the mathematical background to implement that.
In the runproc() methods of classes Ladspa_Moogvcf1,2,3 you will find
some lines like:
if (add) *p1++ += g1 * c4;
else *p1++ = g1 * c4;
Replace c4 by c2 and see what you get. Don't try any tricks with
Ladspa_Moogvcf_4 - it's quite hairy.
Ciao,
--
FA
Io lo dico sempre: l'Italia è troppo stretta e lunga.
22 Jul
22 Jul
6:18 p.m.
On Tue, Jul 21, 2009 at 9:37 AM, Fons Adriaensen<fons(a)kokkinizita.net> wrote:
On Mon, Jul 20, 2009 at 05:11:50PM -0700, Ken Restivo
wrote:
Ken - maybe you already stated this somewhere, but how close does the
CAPS AutoWah come? Maybe it's possible to swap out it's filter with
another implementation? Or raise the upper limit on the Q parameter?
Being a bass player, I've always wanted an AutoFilter plugin
(envelope-controlled LPF). If I get time, I'll start with the CAPS
AutoWah and replace the bandpass with a lowpass.
Thanks. Alas, that seems like a very concise
explanation, but I don't have the mathematical background to implement that.
In the runproc() methods of classes Ladspa_Moogvcf1,2,3 you will find
some lines like:
if (add) *p1++ += g1 * c4;
else *p1++ = g1 * c4;
Replace c4 by c2 and see what you get. Don't try any tricks with
Ladspa_Moogvcf_4 - it's quite hairy.
Ciao,
21 Jul
21 Jul
1:56 p.m.
Really good info; in fact some time ago I tried to figure out how to
analize and reproduce in the digital realm a sound or fx.
But, as Ken, my skills in DSP and programming aren't that good to try
to help in such a deep way. I think I'd be more usefull in analysing
by ear or to contribute with some ideas.
However, what I could do is to provide some more data from a Wah pedal
(borrowed), along with Julien's. In fact, I was considering to buy one
some time ago, but I didn't decided nor what kind (Wah, Cry baby...)
Maybe this is a sign ;)
2009/7/21, Ken Restivo <ken(a)restivo.org>rg>:
On Mon, Jul 20, 2009 at 11:51:07AM +0200, Fons
Adriaensen wrote:
On Sun, Jul 19, 2009 at 08:10:47PM -0700, Ken
Restivo wrote:
Thanks. Alas, that seems like a very concise explanation, but I don't have
the mathematical background to implement that.
If someone feels like modifying the Moog VCF to make it a Vox/Thomas Wah,
I'd be eternally grateful. But it's pretty clear I don't have the skills to
take this over the finish line.
-ken
_______________________________________________
Linux-audio-user mailing list
Linux-audio-user(a)lists.linuxaudio.org
http://lists.linuxaudio.org/mailman/listinfo/linux-audio-user
Just a quick update on the wah research.
A friend owns a Dunlop "Jimi Hendrix Wah", which says it is the
"Original Thomas Design", by which I assume they mean to claim it's the
same design as the Thomas Organ Wah, formerly Vox.
This website's describes the frequency response as a lowpass with a
resonant peak:
http://www.geofex.com/Article_Folders/wahpedl/wahped.htm
So here is what JAPA says it does (and I believe JAPA more than some
random website):
When fully closed, it's a bandpass, with a VERY high Q!
http://restivo.org/misc/lowend-jimi.png
But, wait, when I open it up, suddenly it becomes more like a highpass,
but with a lot of resonance:
http://restivo.org/misc/midrange-jimi.png
When it's fully opened, it's definitely a highpass, but with a helluva
peak:
http://restivo.org/misc/high-jimi.png
So, not only is the opposite of what that article says, but it's also
kind of non-linear. I'll poke around the various LADSPA plugins and see
if I can find something nearly like this.
Another guitar-player friend has a different wah (IIRC, either a "Cry
Baby", or a Morley), and I'll see if I can run his through this and see
what it comes up looking like.
AFAICS this is a resonant (which is not the same as bandpass) filter.
If the response near Fs/2 bcomes flat, that does not mean it is a
highpass.
Remember that any digital filter is 'mirrored' to the other side
of Fs/2. Also the magnitude of the response must be continuous or
zero at all points (for finite order).
The result of all this is that at Fs/2 the response must be either
zero or have a zero derivative, i.e. be horizontal.
In a high order filter you can make the 'roundoff' region near
Fs/2 very small, but it's always there, unless the response is
zero at that frequency.
You can probably get this type of response using the MOOG VCF
by taking the output at a different point in the algorithm.
The MOOG VCF is 4th order, this is overkill as the analog
circuit is very likely to be just 2nd order.
14 Aug
14 Aug
6 p.m.
On Tue, Jul 21, 2009 at 05:56:42PM +0200, Carlos Sanchiavedraz wrote:
Really good info; in fact some time ago I tried to
figure out how to
analize and reproduce in the digital realm a sound or fx.
But, as Ken, my skills in DSP and programming aren't that good to try
to help in such a deep way. I think I'd be more usefull in analysing
by ear or to contribute with some ideas.
However, what I could do is to provide some more data from a Wah pedal
(borrowed), along with Julien's. In fact, I was considering to buy one
some time ago, but I didn't decided nor what kind (Wah, Cry baby...)
Maybe this is a sign ;)
2009/7/21, Ken Restivo <ken(a)restivo.org>rg>:
> On Mon, Jul 20, 2009 at 11:51:07AM +0200, Fons Adriaensen wrote:
>> On Sun, Jul 19, 2009 at 08:10:47PM -0700, Ken Restivo wrote:
>>
>> > Just a quick update on the wah research.
>> >
>> > A friend owns a Dunlop "Jimi Hendrix Wah", which says it is the
>> > "Original Thomas Design", by which I assume they mean to claim
it's the
>> > same design as the Thomas Organ Wah, formerly Vox.
>> >
>> > This website's describes the frequency response as a lowpass with a
>> > resonant peak:
>> > http://www.geofex.com/Article_Folders/wahpedl/wahped.htm
>> >
>> > So here is what JAPA says it does (and I believe JAPA more than some
>> > random website):
>> >
>> > When fully closed, it's a bandpass, with a VERY high Q!
>> > http://restivo.org/misc/lowend-jimi.png
>> >
>> > But, wait, when I open it up, suddenly it becomes more like a highpass,
>> > but with a lot of resonance:
>> > http://restivo.org/misc/midrange-jimi.png
>> >
>> > When it's fully opened, it's definitely a highpass, but with a
helluva
>> > peak:
>> > http://restivo.org/misc/high-jimi.png
>> >
>> > So, not only is the opposite of what that article says, but it's also
>> > kind of non-linear. I'll poke around the various LADSPA plugins and
see
>> > if I can find something nearly like this.
>> >
>> > Another guitar-player friend has a different wah (IIRC, either a "Cry
>> > Baby", or a Morley), and I'll see if I can run his through this
and see
>> > what it comes up looking like.
>>
>>
>> AFAICS this is a resonant (which is not the same as bandpass) filter.
>> If the response near Fs/2 bcomes flat, that does not mean it is a
>> highpass.
>>
>> Remember that any digital filter is 'mirrored' to the other side
>> of Fs/2. Also the magnitude of the response must be continuous or
>> zero at all points (for finite order).
>>
>> The result of all this is that at Fs/2 the response must be either
>> zero or have a zero derivative, i.e. be horizontal.
>>
>> In a high order filter you can make the 'roundoff' region near
>> Fs/2 very small, but it's always there, unless the response is
>> zero at that frequency.
>>
>> You can probably get this type of response using the MOOG VCF
>> by taking the output at a different point in the algorithm.
>>
>> The MOOG VCF is 4th order, this is overkill as the analog
>> circuit is very likely to be just 2nd order.
>>
>
> Thanks. Alas, that seems like a very concise explanation, but I don't have
> the mathematical background to implement that.
>
> If someone feels like modifying the Moog VCF to make it a Vox/Thomas Wah,
> I'd be eternally grateful. But it's pretty clear I don't have the skills
to
> take this over the finish line.
>
I received a suggestion off-list to try the Guitarix plugins, which I did, and got very
good results from it:
http://restivo.org/projects/wah/high-jimi.png
http://restivo.org/projects/wah/guitarixcry-high.png
http://restivo.org/projects/wah/lowend-jimi.png
http://restivo.org/projects/wah/guitarixcry-low.png
http://restivo.org/projects/wah/midrange-jimi.png
http://restivo.org/projects/wah/guitarixcry-mid.png
Part of the difference in the plots is that I wasn't using the correct JAPA settings
for the plots of the actual "Jimi Hendrix Thomas" wah. The frequencies are
different, but that might just be because the Guitarix plugin sweeps higher and lower than
the Jimi pedal.
It sounds great. Now I'm either going to hack together an auto-wah via AMS or
something and an envelope follower, or build myself an Arduino pedal footcontroller.
Funky and fun.
-ken
6:43 p.m.
On Friday 14 August 2009 21:59:53 Ken Restivo wrote:
It sounds great. Now I'm either going to hack
together an auto-wah via AMS
or something and an envelope follower, or build myself an Arduino pedal
footcontroller.
Get a footcontroller or control it from the keyboards modulation-wheel (if not
used otherwise). Auto-Wah sounds crap.
Arnold
7:19 p.m.
On Fri, 14 Aug 2009 22:43:15 +0200
Arnold Krille <arnold(a)arnoldarts.de> wrote:
On Friday 14 August 2009 21:59:53 Ken Restivo wrote:
Nonono
Building an Arduino footpedal will be much more fun :)
Hmmm.
Instead of a pot on one of the analog inputs use a cheap shaft encoder
and count pulses.
Double Hmmm
Fix it so that the index pulse is at exactly the halfway point in the
travel, and it will 'silently' re-calibrate itself every time you pass
throgh that point.
--
Will J Godfrey
http://www.musically.me.uk
It sounds great. Now I'm either going to hack
together an auto-wah via AMS
or something and an envelope follower, or build myself an Arduino pedal
footcontroller.
Get a footcontroller or control it from the keyboards modulation-wheel (if not
used otherwise). Auto-Wah sounds crap.
Arnold
20 Aug
20 Aug
10:21 p.m.
On Fri, Aug 14, 2009 at 10:19:25PM +0100, Folderol wrote:
On Fri, 14 Aug 2009 22:43:15 +0200
Arnold Krille <arnold(a)arnoldarts.de> wrote:
This sounds intriguing. Right now I have an Arduino, and the reason I haven't used it
is because I tried hooking it up to a volume pedal and the noise was so intense it was
spewing out MIDI messages constantly... unusable. I had considered rigging up a passive
analog LPF, or maybe doing some smoothing in software on the Arduino, but ran out of
time/patience.
What would be involved in fitting this kind of encoder to a volume pedal? I can find
guitar-style volume pedals easily, and they're cheap. The advantage is that I could
use a very cheap ATTiny2313 with no ADC instead of an ATMega Arduino. Encoders sound like
the way to go.
On Friday 14 August 2009 21:59:53 Ken Restivo
wrote:
Nonono
Building an Arduino footpedal will be much more fun :)
Hmmm.
Instead of a pot on one of the analog inputs use a cheap shaft encoder
and count pulses.
It sounds great. Now I'm either going to hack
together an auto-wah via AMS
or something and an envelope follower, or build myself an Arduino pedal
footcontroller.
Get a footcontroller or control it from the keyboards modulation-wheel (if not
used otherwise). Auto-Wah sounds crap.
Arnold Double Hmmm
Fix it so that the index pulse is at exactly the halfway point in the
travel, and it will 'silently' re-calibrate itself every time you pass
throgh that point.
I don't know what an "index pulse" is. If you could point me to some good
introductory reading material on dealing with encoders, I'd find it very interesting
indeed.
Thanks.
-ken
10:29 p.m.
On Thu, Aug 20, 2009 at 05:21:10PM -0700, Ken Restivo wrote:
On Fri, Aug 14, 2009 at 10:19:25PM +0100, Folderol
wrote:
An index pulse is a unique output of the encoder that can be recognised
by the microcontroller for some purpose. Usually to recognise a home
position.
The other pulses emitted by the encoder correspond to movement in a
position beyond the index pulse position.
Obviously, you'd need an encoder that has this feature. There are very
simple encoders that don't have it ... e.g. the X and Y optical encoders
in older "non-optical" ball mice.
--
James Cameron
http://quozl.linux.org.au/
Double Hmmm
Fix it so that the index pulse is at exactly the halfway point in the
travel, and it will 'silently' re-calibrate itself every time you pass
throgh that point.
I don't know what an "index pulse" is. If you could point me to some
good introductory reading material on dealing with encoders, I'd find
it very interesting indeed.
21 Aug
21 Aug
8:12 p.m.
On Thu, 20 Aug 2009 17:21:10 -0700
Ken Restivo <ken(a)restivo.org> wrote:
On Fri, Aug 14, 2009 at 10:19:25PM +0100, Folderol
wrote:
Hmmm. The best 'introductory' reading is probably on the arduino forums!
Basically, any half decent encoder has at least three outputs. A, B &
Z or N
A and B are the running pulses and are timed such that as well as
giving you a count, they can also tell you the direction. N or Z is the
index and occurs exactly once per revolution of the encoder.
So, as an example if you have a 500 pulse encoder and fix it to a
pedal so you have 180deg of movement you'll actually get a useful 250
pulses. Position the encoder shaft so that the index comes at 90deg and
you'll be able to count +/- 125 pulses and seeing as MIDI only gives
you 127 for most operations that's nearly twice what you need.
Hmmm again. I'm used to just handling these and not having to buy
them. Just looked up on RS and the cheapest one that fits the bill is
about 40 squids :(
http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduc…
--
Will J Godfrey
http://www.musically.me.uk
On Fri, 14 Aug 2009 22:43:15 +0200
Arnold Krille <arnold(a)arnoldarts.de> wrote:
This sounds intriguing. Right now I have an Arduino, and the reason I haven't used it
is because I tried hooking it up to a volume pedal and the noise was so intense it was
spewing out MIDI messages constantly... unusable. I had considered rigging up a passive
analog LPF, or maybe doing some smoothing in software on the Arduino, but ran out of
time/patience.
What would be involved in fitting this kind of encoder to a volume pedal? I can find
guitar-style volume pedals easily, and they're cheap. The advantage is that I could
use a very cheap ATTiny2313 with no ADC instead of an ATMega Arduino. Encoders sound like
the way to go.
On Friday 14 August 2009 21:59:53 Ken Restivo
wrote:
Nonono
Building an Arduino footpedal will be much more fun :)
Hmmm.
Instead of a pot on one of the analog inputs use a cheap shaft encoder
and count pulses.
It sounds great. Now I'm either going to hack
together an auto-wah via AMS
or something and an envelope follower, or build myself an Arduino pedal
footcontroller.
Get a footcontroller or control it from the keyboards modulation-wheel (if not
used otherwise). Auto-Wah sounds crap.
Arnold Double Hmmm
Fix it so that the index pulse is at exactly the halfway point in the
travel, and it will 'silently' re-calibrate itself every time you pass
throgh that point.
I don't know what an "index pulse" is. If you could point me to some good
introductory reading material on dealing with encoders, I'd find it very interesting
indeed.
Thanks.
-ken 
15 Aug
15 Aug
10:14 a.m.
Am Freitag, den 14.08.2009, 12:59 -0700 schrieb Ken Restivo:
On Tue, Jul 21, 2009 at 05:56:42PM +0200, Carlos
Sanchiavedraz wrote:
Hi
The crybaby(wah) from guitarix is the original crybaby from Professor
Julius O. Smith as he describes here:
http://ccrma.stanford.edu/realsimple/faust_strings/Adding_Wah_Pedal.html
It's included in the faust distribution and there you can find also a
description (in the Documentation) how to make it a auto wah.
http://faust.grame.fr/
Anyway, . .
have fun
hermann
Really good info; in fact some time ago I tried
to figure out how to
analize and reproduce in the digital realm a sound or fx.
But, as Ken, my skills in DSP and programming aren't that good to try
to help in such a deep way. I think I'd be more usefull in analysing
by ear or to contribute with some ideas.
However, what I could do is to provide some more data from a Wah pedal
(borrowed), along with Julien's. In fact, I was considering to buy one
some time ago, but I didn't decided nor what kind (Wah, Cry baby...)
Maybe this is a sign ;)
2009/7/21, Ken Restivo <ken(a)restivo.org>rg>:
> On Mon, Jul 20, 2009 at 11:51:07AM +0200, Fons Adriaensen wrote:
>> On Sun, Jul 19, 2009 at 08:10:47PM -0700, Ken Restivo wrote:
>>
>> > Just a quick update on the wah research.
>> >
>> > A friend owns a Dunlop "Jimi Hendrix Wah", which says it is the
>> > "Original Thomas Design", by which I assume they mean to claim
it's the
>> > same design as the Thomas Organ Wah, formerly Vox.
>> >
>> > This website's describes the frequency response as a lowpass with a
>> > resonant peak:
>> > http://www.geofex.com/Article_Folders/wahpedl/wahped.htm
>> >
>> > So here is what JAPA says it does (and I believe JAPA more than some
>> > random website):
>> >
>> > When fully closed, it's a bandpass, with a VERY high Q!
>> > http://restivo.org/misc/lowend-jimi.png
>> >
>> > But, wait, when I open it up, suddenly it becomes more like a highpass,
>> > but with a lot of resonance:
>> > http://restivo.org/misc/midrange-jimi.png
>> >
>> > When it's fully opened, it's definitely a highpass, but with a
helluva
>> > peak:
>> > http://restivo.org/misc/high-jimi.png
>> >
>> > So, not only is the opposite of what that article says, but it's also
>> > kind of non-linear. I'll poke around the various LADSPA plugins and
see
>> > if I can find something nearly like this.
>> >
>> > Another guitar-player friend has a different wah (IIRC, either a "Cry
>> > Baby", or a Morley), and I'll see if I can run his through this
and see
>> > what it comes up looking like.
>>
>>
>> AFAICS this is a resonant (which is not the same as bandpass) filter.
>> If the response near Fs/2 bcomes flat, that does not mean it is a
>> highpass.
>>
>> Remember that any digital filter is 'mirrored' to the other side
>> of Fs/2. Also the magnitude of the response must be continuous or
>> zero at all points (for finite order).
>>
>> The result of all this is that at Fs/2 the response must be either
>> zero or have a zero derivative, i.e. be horizontal.
>>
>> In a high order filter you can make the 'roundoff' region near
>> Fs/2 very small, but it's always there, unless the response is
>> zero at that frequency.
>>
>> You can probably get this type of response using the MOOG VCF
>> by taking the output at a different point in the algorithm.
>>
>> The MOOG VCF is 4th order, this is overkill as the analog
>> circuit is very likely to be just 2nd order.
>>
>
> Thanks. Alas, that seems like a very concise explanation, but I don't have
> the mathematical background to implement that.
>
> If someone feels like modifying the Moog VCF to make it a Vox/Thomas Wah,
> I'd be eternally grateful. But it's pretty clear I don't have the skills
to
> take this over the finish line.
>
I received a suggestion off-list to try the Guitarix plugins, which I did, and got very
good results from it:
http://restivo.org/projects/wah/high-jimi.png
http://restivo.org/projects/wah/guitarixcry-high.png
http://restivo.org/projects/wah/lowend-jimi.png
http://restivo.org/projects/wah/guitarixcry-low.png
http://restivo.org/projects/wah/midrange-jimi.png
http://restivo.org/projects/wah/guitarixcry-mid.png
Part of the difference in the plots is that I wasn't using the correct JAPA settings
for the plots of the actual "Jimi Hendrix Thomas" wah. The frequencies are
different, but that might just be because the Guitarix plugin sweeps higher and lower than
the Jimi pedal.
It sounds great. Now I'm either going to hack together an auto-wah via AMS or
something and an envelope follower, or build myself an Arduino pedal footcontroller.
Funky and fun.
-ken
_______________________________________________ 
23 Jul
23 Jul
8:21 p.m.
that.
If someone feels like modifying the Moog VCF to make it a Vox/Thomas Wah,
I'd be eternally grateful. But it's pretty clear I don't have the skills to
take this over the finish line.
I have been using Fon's Moog VCF as a wah pedal for a while, but to get an
effect that works fully to my ear I also use the Glame Analog bandpass
filter. The two filters are on a Jack-rack with the frequency and the input
gain of the VCF and the center frequency of the bandpass all set to the same
midi CC which I control with a footswitch. The reason for the input gain was
that I found the perceived volume dropped off at the higher ranges of the
wah. This is all linear since as far as I know, Jack-rack can only do
linear. I might try to set this up in AMS which can do log which might sound
better.
Not an auto-wah, but good for guitar wah.
20 Jul
20 Jul
11:07 a.m.
Hi,
Wouldn't it be better to do these kind of measurements in JAAA?
Cheers,
Andrés
On Sun, Jul 19, 2009 at 10:10 PM, Ken Restivo<ken(a)restivo.org> wrote:
Just a quick update on the wah research.
A friend owns a Dunlop "Jimi Hendrix Wah", which says it is the "Original
Thomas Design", by which I assume they mean to claim it's the same design as the
Thomas Organ Wah, formerly Vox.
This website's describes the frequency response as a lowpass with a resonant peak:
http://www.geofex.com/Article_Folders/wahpedl/wahped.htm
So here is what JAPA says it does (and I believe JAPA more than some random website):
When fully closed, it's a bandpass, with a VERY high Q!
http://restivo.org/misc/lowend-jimi.png
But, wait, when I open it up, suddenly it becomes more like a highpass, but with a lot of
resonance:
http://restivo.org/misc/midrange-jimi.png
When it's fully opened, it's definitely a highpass, but with a helluva peak:
http://restivo.org/misc/high-jimi.png
So, not only is the opposite of what that article says, but it's also kind of
non-linear. I'll poke around the various LADSPA plugins and see if I can find
something nearly like this.
Another guitar-player friend has a different wah (IIRC, either a "Cry Baby", or
a Morley), and I'll see if I can run his through this and see what it comes up looking
like.
-ken
_______________________________________________
Linux-audio-user mailing list
Linux-audio-user(a)lists.linuxaudio.org
http://lists.linuxaudio.org/mailman/listinfo/linux-audio-user
--
Andrés
8:59 p.m.
On Mon, Jul 20, 2009 at 08:07:03AM -0500, Andres Cabrera wrote:
Wouldn't it be better to do these kind of
measurements in JAAA?
For accurate technical measurements yes, to get an
easy to understand global picture of what a filter
is doing JAPA is a lot more practical.
Ciao,
--
FA
Io lo dico sempre: l'Italia è troppo stretta e lunga.
5601
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linux-audio-user@lists.linuxaudio.org
22 comments
12 participants
participants (12)
-
Andres Cabrera -
Arnold Krille -
Bill Allen -
Carlos Sanchiavedraz -
Folderol -
Fons Adriaensen -
hermann -
James Cameron -
Julien Claassen -
Justin Smith -
Ken Restivo -
Paul Coccoli