electro-music.com   Dedicated to experimental electro-acoustic
and electronic music
 
    Front Page  |  Articles  |  Radio
 |  Media  |  Forum  |  Wiki  |  Links  |  Store
Forum with support of Syndicator RSS
 FAQFAQ   CalendarCalendar   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   LinksLinks
 RegisterRegister   ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in  Chat RoomChat Room 
 Forum index » DIY Hardware and Software » Ken Stone designs - CGS
Dome filter
Post new topic   Reply to topic Moderators: Scott Stites
Page 1 of 1 [18 Posts]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
Author Message
neandrewthal



Joined: May 11, 2007
Posts: 672
Location: Canada

PostPosted: Thu Nov 13, 2008 2:17 am    Post subject: Dome filter
Subject description: What exaclty does it do?
Reply with quote  Mark this post and the followings unread

There is hardly anything written on the dome filter, but if I were to take a guess at what it does, I would say you insert a signal and it shifts it 90 degrees. IMO this would be incredibly useful, so therefore I must be wrong, since Ken's page says it is not a stand-alone project or of use to most people. So, is there any other use for it besides the basis of a frequency shifter? Also, does anyone know of a module that will perform the function I described?
_________________
" I went through quite a few trannies til I found one I liked" - Wild Zebra
Back to top
View user's profile Send private message
Luka



Joined: Jun 29, 2007
Posts: 1002
Location: Melb.

PostPosted: Thu Nov 13, 2008 3:07 am    Post subject: Reply with quote  Mark this post and the followings unread

sounds like what the mankato does
perhaps read more up on that design

_________________
problemchild
melbourne australia
http://cycleofproblems.blogspot.com/
http://www.last.fm/user/prblmchild
Back to top
View user's profile Send private message
yusynth



Joined: Nov 24, 2005
Posts: 1293
Location: France

PostPosted: Thu Nov 13, 2008 3:22 am    Post subject: Reply with quote  Mark this post and the followings unread

Luka wrote:
sounds like what the mankato does
perhaps read more up on that design


Not exactly the same, the dome filter is intended to be an allpass filter which provides with a 90° phase shift over all the frequency range, while the mankato provides a 90° phase shift at the cut-off frequency.

To answer the first question, yes the first application is that of frequency shifter. It may also be used as frequency doubler if you feed the two pase shifted outputs to the two inputs of a balanced modulator (MC1496 or other), since the phase shift is constant over a wide bandpass, all the partials are doubled in frequency.

Another application is to create a spacialization of a monophonic source : feed two outputs to separate inputs of a stereo mixer and set the pan pots to a different position and the monophonic sound will spread over a solid angle.

_________________
Yves
Back to top
View user's profile Send private message Visit poster's website
Luka



Joined: Jun 29, 2007
Posts: 1002
Location: Melb.

PostPosted: Thu Nov 13, 2008 4:05 am    Post subject: Reply with quote  Mark this post and the followings unread

shouldnt that be called a phase shifter instead of a filter then?
_________________
problemchild
melbourne australia
http://cycleofproblems.blogspot.com/
http://www.last.fm/user/prblmchild
Back to top
View user's profile Send private message
yusynth



Joined: Nov 24, 2005
Posts: 1293
Location: France

PostPosted: Thu Nov 13, 2008 4:53 am    Post subject: Reply with quote  Mark this post and the followings unread

It is a phase shifter, but such a device is what is primarily called an all-pass filter.
_________________
Yves
Back to top
View user's profile Send private message Visit poster's website
neandrewthal



Joined: May 11, 2007
Posts: 672
Location: Canada

PostPosted: Thu Nov 13, 2008 11:53 am    Post subject: Reply with quote  Mark this post and the followings unread

yusson wrote:
Luka wrote:
sounds like what the mankato does
perhaps read more up on that design


Not exactly the same, the dome filter is intended to be an allpass filter which provides with a 90° phase shift over all the frequency range, while the mankato provides a 90° phase shift at the cut-off frequency.


So, say you put in a sawtooth and shift it 90° over the whole frequency range. Does it still look like a sawtooth after?

I love the mankato, but it's such a nice filter as well, and only does sine waves. I've been looking at the ChaQuo too, but once again it's only sines and has no voltage control. What we need is a module that will turn any source into a quadrature oscillator Cool

_________________
" I went through quite a few trannies til I found one I liked" - Wild Zebra
Back to top
View user's profile Send private message
yusynth



Joined: Nov 24, 2005
Posts: 1293
Location: France

PostPosted: Thu Nov 13, 2008 12:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

neandrewthal wrote:
So, say you put in a sawtooth and shift it 90° over the whole frequency range. Does it still look like a sawtooth after?


If your dome filter is perfect, yes, I think so.

_________________
Yves
Back to top
View user's profile Send private message Visit poster's website
neandrewthal



Joined: May 11, 2007
Posts: 672
Location: Canada

PostPosted: Thu Nov 13, 2008 1:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

yusson wrote:
neandrewthal wrote:
So, say you put in a sawtooth and shift it 90° over the whole frequency range. Does it still look like a sawtooth after?


If your dome filter is perfect, yes, I think so.


Hmm, well what do you mean by "perfect"? 0.1% resistors and such? I guess the slightest error would produce a nasty glitch in your waveform?

If the CGS dome filter can do this, then I can't understand why Ken basically labels it as useless Confused

_________________
" I went through quite a few trannies til I found one I liked" - Wild Zebra
Back to top
View user's profile Send private message
Blue Hell
Site Admin


Joined: Apr 03, 2004
Posts: 22166
Location: The Netherlands, Enschede
Audio files: 208
G2 patch files: 319

PostPosted: Thu Nov 13, 2008 2:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

I think a couple of things get mixed up here? As I understand things there are constant time delay filters and there are constant phase filters. And these are different things; a constant time delay would result in a linearly changing phase.

A constant time delay filter will pass arbitrary waveforms unchanged but delayed in time, this is used for phasers for instance. A constant phase filter, like the dome filter (why is it called a dome filter BTW?) used by Ken Stone (and also Jürgen Haible ), can be used for frequency shifters. These will not pass arbitrary waveforms with unchanged shape (but as the spectral content is not changed the filtered signal should still sound the same I think ...)

Some refs :

http://www.jhaible.heim.at/fs1a/fs1a.html
http://www.cgs.synth.net/modules/cgs45_domefilter.html
http://en.wikipedia.org/wiki/All-pass_filter

_________________
Jan
Back to top
View user's profile Send private message Visit poster's website
yusynth



Joined: Nov 24, 2005
Posts: 1293
Location: France

PostPosted: Thu Nov 13, 2008 2:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

By perfect, I mean a 90° shift within 0.1% over a 30kHz bandpass (and this is difficult to achieve when you consider the tolerance of components). If not, some partial will not be in phase and this might change the output waveshape (though the harmonic amplitudes are maintained).

I think Ken meant that the dome filter on it's own is useless but that one has to experiment by combining it with other circuits to find some interesting applications. In other words this is not a "plug-in" board, it is a more demanding circuit.

_________________
Yves
Back to top
View user's profile Send private message Visit poster's website
certain2



Joined: Nov 21, 2008
Posts: 5
Location: yorkshire

PostPosted: Tue Jun 30, 2009 11:54 am    Post subject: Reply with quote  Mark this post and the followings unread

>>A constant phase filter, like the dome filter (why is it called a dome filter BTW?)

Robert B. Dome,
"Phase Shift System", Canadian Patent CA490405, 1953

You can get it from http://ep.espacenet.com/ Do a number search
or smart search on CA490405

He apparently worked for General Electric, Canada and had a
large number of patents on tube/valve audio/video circuits.
Back to top
View user's profile Send private message
CJ Miller



Joined: Jan 07, 2007
Posts: 370
Location: 127.0.0.1

PostPosted: Mon Jul 20, 2009 2:35 am    Post subject: values I used Reply with quote  Mark this post and the followings unread

I finally got myself to brave stuffing my Dome boards... The formula for the recommended component values is screened onto the top, and I had already read about the circuit in Electronotes #83. Since I had the suggested capacitors I decided to fuss with resistor values, since I have more to choose from. It took me about four hours of going through resistors and measuring to get these close, so hopefully this might save somebody some time.

Stage cap resistance (used)
1 .47uF 62.6k (62.2k+330r)
2 .47uf 8.24k (8.25k)
3 .047uF 20.3k (12.1k+8.25k)
4 .0082uF 28.9k (27.4k+1.5k)
5 .0082uF 7.20k (6.81k+487r)
6 .0082uF 1.62k (820r+820r)

7 .47uF 18.0k (16.5k+1.5k)
8 .047uF 40.6k (39.2k+1.5k)
9 .0082uF 57.9k (49.9k+8.25k)
10 .0082uF 14.4k (14k+487r)
11 .0082uF 3.55k (2.21k+1.37k)
12 .0082uF 467r (180r+287r)

This was the easist to do with what i had on hand. It still took lots of measuring various combinations, sometimes even trying the same value from different manufacturers. Still I was able to get within a few hundreths for each value, many of them spot on.

As for what to do with these? I was thinking I might build something like the Electronotes frequency shifter, but unlike most people's leave it more openly modular so the subcircuits can be blocks to be patched. Why not have a high-frequency sine VCO, multipliers, and phase networks to play with? It'll be a while yet though, I am still building my basic setup.
Back to top
View user's profile Send private message
zthee



Joined: Feb 20, 2008
Posts: 414
Location: Stockholm

PostPosted: Mon Jul 20, 2009 3:58 am    Post subject: Reply with quote  Mark this post and the followings unread

So let's say I build 2 of these boards.
I use one for the carrier and one for the signal. Then I use a balanced modulator, like the MC1496 and sum/multiply them together. And I got a Frequency shifter?

It sounds a little bit to straight forward.. So what's the catch?

Can I use anything else instead of the MC1496? I guess a normal ring modulator wouldn't do?

_________________
http://www.thehumancomparator.net/
Back to top
View user's profile Send private message
CJ Miller



Joined: Jan 07, 2007
Posts: 370
Location: 127.0.0.1

PostPosted: Mon Jul 20, 2009 5:41 am    Post subject: Reply with quote  Mark this post and the followings unread

zthee wrote:
It sounds a little bit to straight forward.. So what's the catch?


The catch is that it's a fairly large, involved project. It probably requires lots of adjustment. As I understand it, first one uses a pair of multipliers in parallel on a fixed 20kHZ oscillator and a quadrature VCO. Then we'd process our signal of choice through a Dome filter. The VCO sine and Dome sine are routed through a multiplier, and their cosines are routed through another multiplier. The multipliers outputs are summed and passed through VCAs which use an envelope extracted from the input signal.

zthee wrote:
Can I use anything else instead of the MC1496? I guess a normal ring modulator wouldn't do?


You could use MC1496, but a more precision multiplier would probably be far less noisy. It is already a drastic effect, and people say that too little linearity between it's input and output detracts from it's usefulness. If it gets too noisy, the output might not resemble the input any longer! The original called for AD533, but the newer AD633 will probably be fine.

Personally I think it might be fun to try non-standard settings. What if the phases aren't 90 degrees? What if the phases are changing? What if the quadrature VCO can do more complex waveshapes than sine? And yes, it is possible to use a second Dome filter instead of a VCO, but the result would be very complex. I don't know if I'd like the sound, but I want to hear these things.

I recommend Jurgen Haible's page on frequency shifting, where he explains his circuit. I am a noob and only beginning to understand this.
Back to top
View user's profile Send private message
zthee



Joined: Feb 20, 2008
Posts: 414
Location: Stockholm

PostPosted: Mon Jul 20, 2009 6:37 am    Post subject: Reply with quote  Mark this post and the followings unread

CJ Miller wrote:
Personally I think it might be fun to try non-standard settings. What if the phases aren't 90 degrees? What if the phases are changing? What if the quadrature VCO can do more complex waveshapes than sine? And yes, it is possible to use a second Dome filter instead of a VCO, but the result would be very complex. I don't know if I'd like the sound, but I want to hear these things.


Yes, this is what I'm interested in!

I built Haibles FS1A a few months ago and I like it. But I'd like one that could be very experimental as well.

Here's my idea. Removing the oscillator from the FS1A and keeping the compander (orange), the modulator (green) and the VCAs (pink).

So you feed the input signal to the input and cmp_out to the dome filter. The other you feed straight into the dome filter, then put the signal from the first dome filter into sig_sin and sig_cos. And from the other filter you have the input at R58 and R77..?

(I hope it's OK with mr. Haible that I post mutilated pictures of his schematics! If not I'll remove it straight away!).


jh_fs1a_schematics_board_1.jpg
 Description:
 Filesize:  301.37 KB
 Viewed:  420 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

jh_fs1a_schematics_board_1.jpg



_________________
http://www.thehumancomparator.net/
Back to top
View user's profile Send private message
angakok_thoth



Joined: Sep 02, 2016
Posts: 2
Location: Prague

PostPosted: Fri Sep 02, 2016 7:02 pm    Post subject: Reply with quote  Mark this post and the followings unread

yusynth wrote:
neandrewthal wrote:
So, say you put in a sawtooth and shift it 90° over the whole frequency range. Does it still look like a sawtooth after?


If your dome filter is perfect, yes, I think so.


No it won't *look* like sawtooth, if we are talking about the shape of the wave (which will change) and not about it's harmonic content and sound (which will stay the same).

Even if the dome filter would do 90deg shift, it would not look as saw-wave anymore. Imagine the saw-wave decomposed into its sine-wave components - each component has a different wavelength, so for each of them the 90degrees shift means a delay by different time... When you add them up back together, the shape is different. (i believe it's like that for all waves other than single pure single sine-wave without any harmonics and for any amount of phaseshifts except for 0deg and multiples of 360deg)

...and this dome filter doesn't do 90deg phase shift to the input anyway. What this dome filter does, is creating two outputs with 90deg phase shift between them. So it is not 90deg phase shift between input and output, it is between output1 and output2. And neither of them will look like saw. But will sound the same.
Back to top
View user's profile Send private message
angakok_thoth



Joined: Sep 02, 2016
Posts: 2
Location: Prague

PostPosted: Fri Sep 02, 2016 9:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

Found my old patch, where I was checking exactly that - how a saw would look after various phase shifts.
Attached a screenshot of 0/30/45/60/90 degree shifts. (It's not very smooth as the saw is made using 12 sine oscillators...)


saw_phase_shifts.png
 Description:
 Filesize:  10.96 KB
 Viewed:  51 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

saw_phase_shifts.png


Back to top
View user's profile Send private message
L´Andratté



Joined: Sep 23, 2012
Posts: 120
Location: Hamburg, Germany
Audio files: 5

PostPosted: Wed Dec 07, 2016 7:25 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the information, angakok_toth!
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic Moderators: Scott Stites
Page 1 of 1 [18 Posts]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
 Forum index » DIY Hardware and Software » Ken Stone designs - CGS
Jump to:  

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum
e-m mkii

Please support our site. If you click through and buy from
our affiliate partners, we earn a small commission.


Forum with support of Syndicator RSS
Powered by phpBB © 2001, 2005 phpBB Group
Copyright © 2003 through 2009 by electro-music.com - Conditions Of Use