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 » Instruments and Equipment » Strings and things
Alternate Guitar Pickup Concepts
Post new topic   Reply to topic Moderators: BobTheDog
Page 2 of 2 [45 Posts]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
Goto page: Previous 1, 2
Author Message
Inventor
Stream Operator


Joined: Oct 13, 2007
Posts: 5978
Location: San Antonio, Tx, USA
Audio files: 258

PostPosted: Wed Dec 31, 2008 5:32 am    Post subject: Reply with quote  Mark this post and the followings unread

DrJustice wrote:
urbanscallywag wrote:
From what I can find, guitar pickups act as LPF not BPF as mentioned here. It makes sense, bass guitars go pretty low. A guitar pickup maker told me the frequency response of an electric guitar is basically dictated by the cabinet.

The coil itself is an LPF, it passes DC after all. But the pickup function seems to exhibit a band pass response. The output of the guitar is not AC coupled, and if I move a string very slowly by hand, even with a huge deflection, I get no detectable signal.

DJ
--

Oooohhhh, now it makes sense. I looked up Faraday's law of induction on Wikipedia, here's the link:

http://en.wikipedia.org/wiki/Faraday%27s_law_of_induction

The formula for the generated voltage is E=B*l*v, so the voltage is directly proportional to the velocity of the string. Velocity would, i suppose, be a sum of sinusoids with both amplitude and frequency.

_________________
"Let's make noise for peace." - Kijjaz
Back to top
View user's profile Send private message Send e-mail
DrJustice



Joined: Sep 13, 2004
Posts: 2048
Location: Morokulien
Audio files: 3

PostPosted: Wed Dec 31, 2008 6:34 am    Post subject: Reply with quote  Mark this post and the followings unread

Inventor wrote:
The formula for the generated voltage is E=B*l*v, so the voltage is directly proportional to the velocity of the string.

Right, thank you for looking it up! It's been an eon since I had to think about any of that... So the string/pickup interaction does not "pass DC" as in a static string position giving a corresponding DC voltage (naturally). So it's a BPF, and the coil itself is an LPF. It'll be interesting to model this Smile

DJ
--
Back to top
View user's profile Send private message Visit poster's website
Oskar



Joined: Jul 29, 2004
Posts: 1738
Location: Norway

PostPosted: Thu Jan 01, 2009 2:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

I'm really impressed by you guys' technical know-how! Tbh, it's well beyond me, but keep up the good work! Smile
_________________
Where there are too many policemen, there is no liberty. Where there are too many soldiers, there is no peace. Where there are too many lawyers, there is no justice.
Lin Yutang (1895-1976)
Back to top
View user's profile Send private message
urbanscallywag



Joined: Nov 30, 2007
Posts: 317
Location: sometimes

PostPosted: Thu Jan 01, 2009 2:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

I see what you're saying, and it makes sense that a slow movement wouldn't generate much flux...or something. Smile
Back to top
View user's profile Send private message
urbanscallywag



Joined: Nov 30, 2007
Posts: 317
Location: sometimes

PostPosted: Thu Jan 01, 2009 5:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

DrJustice,

You were talking about no detectable signal on a scope, right?

Although I do agree that the string -> pickup does not pass DC and therefore is technically considered a BPF I think the whole system has no practical lower limit as far as audio is concerned, I expect most pickups would go down to 20 Hz or less. Any perceived BPF effect is from the high Q LPF as discussed.

Inventor I do see what you're saying about having a flat frequency response by taking the signal from the string rather than the pickup.

Now all of the sudden I'm interested in building a Moog-like infinite sustain guitar with DSP instead of analog. One thing I don't understand is how to couple energy back into the string.
Back to top
View user's profile Send private message
DrJustice



Joined: Sep 13, 2004
Posts: 2048
Location: Morokulien
Audio files: 3

PostPosted: Thu Jan 01, 2009 5:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

urbanscallywag wrote:

You were talking about no detectable signal on a scope, right?

Yes.
Quote:

Although I do agree that the string -> pickup does not pass DC and therefore is technically considered a BPF I think the whole system has no practical lower limit as far as audio is concerned, I expect most pickups would go down to 20 Hz or less. Any perceived BPF effect is from the high Q LPF as discussed.

There has to be a lower lower limit, considering that you'd not want to deal with close to infinitely weak signals. Exactly what the practical lower limit is depends on your preference for minimum signal strength. Since E=B*l*v, as v goes towards 0, so does E. Just like a high pass filter (e.g. a capacitor in series) stop band rejection reaches infinity only at f=0 (DC). The Q of the LPF would go towards enhancing the BPF response of the whole system. I agree that at 20Hz, the signal is probably still usable - since E is proprtional to v, it's easy enough to determine for a given application; the volume drops by 6dB for each halving of v.

Quote:
Now all of the sudden I'm interested in building a Moog-like infinite sustain guitar with DSP instead of analog. One thing I don't understand is how to couple energy back into the string.

Come on urban, go right ahead and start the research - the guitar world needs more new stuff Smile

DJ
--
Back to top
View user's profile Send private message Visit poster's website
urbanscallywag



Joined: Nov 30, 2007
Posts: 317
Location: sometimes

PostPosted: Thu Jan 01, 2009 6:46 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ehk, math. Wink

I would just say its intuitive that if you move the string with your hand its probably moving less than a Hertz, so I wouldn't expect anything to register since hardly any flux is generated. Luckily that's not audio anyhow. A 5 string bass's lowest string is tuned to ~30 Hz. I'm not sure how much different a guitar pickup is than a bass pickup but I'm sure its goes "low enough".

Another way to look at it: a Moog (or most any filter) is AC coupled but is still considered a LPF, not a BPF.

Haha that detail aside, I've had some ideas for a long time about things to do with a hex pickup and DSP. One of these days... Laughing
Back to top
View user's profile Send private message
urbanscallywag



Joined: Nov 30, 2007
Posts: 317
Location: sometimes

PostPosted: Thu Jan 01, 2009 6:53 pm    Post subject: Reply with quote  Mark this post and the followings unread

So I agree that this concept is interesting for building pickups that can have an arbitrary frequency response. thumright
Back to top
View user's profile Send private message
Inventor
Stream Operator


Joined: Oct 13, 2007
Posts: 5978
Location: San Antonio, Tx, USA
Audio files: 258

PostPosted: Thu Jan 01, 2009 6:57 pm    Post subject: Reply with quote  Mark this post and the followings unread

Well, one thing to consider is that on a guitar the fundamental frequency is lower in amplitude than the following (2nd) harmonic. This must in part be due to the fact that we don't pluck the string in the middle, so excitation is lower at the fundamental, and possibly in part due to this velocity-dependent characteristic. How much of either is responsible I don't know.

I have made long-sustain in ChucK simply by using automatic gain control. In my case, I rectified the signal and low pass filtered that, then divided the input signal by that slowly changing value. There are practical limits as the signal goes down into the noise so I set up a maximum amount of ACG as well. That's just one way to enhance sustain.

_________________
"Let's make noise for peace." - Kijjaz
Back to top
View user's profile Send private message Send e-mail
Inventor
Stream Operator


Joined: Oct 13, 2007
Posts: 5978
Location: San Antonio, Tx, USA
Audio files: 258

PostPosted: Thu Jan 01, 2009 6:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

urbanscallywag wrote:
So I agree that this concept is interesting for building pickups that can have an arbitrary frequency response. thumright

Kewl and thanks!

_________________
"Let's make noise for peace." - Kijjaz
Back to top
View user's profile Send private message Send e-mail
urbanscallywag



Joined: Nov 30, 2007
Posts: 317
Location: sometimes

PostPosted: Thu Jan 01, 2009 7:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

I didn't know that the fundamental doesn't have the largest amplitude. That complicates things!

http://www.theory.physics.ubc.ca/341-07/pluck/pluck.html

http://www.acoustics.org/press/155th/chapman.htm
Back to top
View user's profile Send private message
Inventor
Stream Operator


Joined: Oct 13, 2007
Posts: 5978
Location: San Antonio, Tx, USA
Audio files: 258

PostPosted: Thu Jan 01, 2009 7:48 pm    Post subject: Reply with quote  Mark this post and the followings unread

urbanscallywag, you find the best links! Thanks.
_________________
"Let's make noise for peace." - Kijjaz
Back to top
View user's profile Send private message Send e-mail
urbanscallywag



Joined: Nov 30, 2007
Posts: 317
Location: sometimes

PostPosted: Thu Jan 01, 2009 8:02 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey you bring up interesting things to search out.

What bothers me is the inconsistency, it appears that sometimes the fundamental is the largest tone, sometimes not. That really does make processing a huge pain.
Back to top
View user's profile Send private message
urbanscallywag



Joined: Nov 30, 2007
Posts: 317
Location: sometimes

PostPosted: Thu Jan 01, 2009 8:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

http://online.physics.uiuc.edu/courses/phys498pom/Student_Projects/Fall02/RLee/Ryan_Lee_P398EMI_Main_Report.pdf

Has some beautiful guitar pluck plots. More of his work can be found here:

http://online.physics.uiuc.edu/courses/phys498pom/498pom_student_projects_fall02.html
Back to top
View user's profile Send private message
Inventor
Stream Operator


Joined: Oct 13, 2007
Posts: 5978
Location: San Antonio, Tx, USA
Audio files: 258

PostPosted: Thu Jul 23, 2009 6:07 am    Post subject: Reply with quote  Mark this post and the followings unread

Just bumping this thread to let you know that prototype #1 was completed a month or two ago and it sounds great (no plinking and rich tone). We are now assembling our first kit for our first customer who will receive serial number 3. Thanks for your interest in the project, this is fun!

Les

_________________
"Let's make noise for peace." - Kijjaz
Back to top
View user's profile Send private message Send e-mail
jksuperstar



Joined: Aug 20, 2004
Posts: 2488
Location: Denver
Audio files: 1
G2 patch files: 18

PostPosted: Fri Jul 31, 2009 2:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey Guys, I happen to play bass, with a low B string (~30Hz)...what are your experiences with bass and this pickup method? Is there something I can do to help this be applied to Bass?

I'm always looking for cleaner pickups...
Back to top
View user's profile Send private message Visit poster's website
Inventor
Stream Operator


Joined: Oct 13, 2007
Posts: 5978
Location: San Antonio, Tx, USA
Audio files: 258

PostPosted: Fri Jul 31, 2009 2:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey man, I want to get this into Bass also, and I think it's quite do-able.

The main problem is the the signal strength is a function of string velocity, and lower frequency strings have lower string velocity because obviously they just don't wiggle as fast! But they wiggle bigger which makes for higher velocities, and I wouldn't be surprised if we could sneak some more magnets under the strings on a bass to boost the signal even more.

Furthermore, even if you don't get full signal, what you do is just turn on the distortion preamp and it acts like a boost. You actually get something similar to clean signal out of your distortion amp setting, which we did for the initial testing before we got the fancy transformers.

If you want to get into this for a bass, I'd suggest buying a kit. It costs about what a pickup upgrade would cost, so you won't be paying too much. Just a thought. We could also provide you with part numbers to order your own kit, but hey, let us grow the biz here a little you know...

Les

_________________
"Let's make noise for peace." - Kijjaz
Back to top
View user's profile Send private message Send e-mail
Inventor
Stream Operator


Joined: Oct 13, 2007
Posts: 5978
Location: San Antonio, Tx, USA
Audio files: 258

PostPosted: Fri Jul 31, 2009 2:30 pm    Post subject: Reply with quote  Mark this post and the followings unread

Now that I think of it, for a bass you might go with 12 mm magnets. On a six-string we use 9 mm magnets even though they are a little shy of the 10 mm that we want and they work well enough. So I think the magnet width is not critical but with a bass the spacing is farther apart I believe. Transformer and switch would be the same, wire, tape, heat shrink the same... Just different magnets is all.

I'd also be concerned about the transformer frequency response. If it is not low enough, then we have a capacitor trick that boosts the low range for any given transformer - pretty neat and might be necessary.

Les

_________________
"Let's make noise for peace." - Kijjaz
Back to top
View user's profile Send private message Send e-mail
jksuperstar



Joined: Aug 20, 2004
Posts: 2488
Location: Denver
Audio files: 1
G2 patch files: 18

PostPosted: Fri Jul 31, 2009 3:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yes, bass strings are much wider spaced than guitar strings. I'll look into the details. For now, freemods.com is blocked by my workplace and categorized as "Gambling". Go figure...
Back to top
View user's profile Send private message Visit poster's website
Inventor
Stream Operator


Joined: Oct 13, 2007
Posts: 5978
Location: San Antonio, Tx, USA
Audio files: 258

PostPosted: Fri Jul 31, 2009 5:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

Oh, freedomodds.com was originally a gambling site. I figured out how to beat the books in basketball with my Perl programs, or so it seems to be in retrospect. I need to make a new web space now.

Les

_________________
"Let's make noise for peace." - Kijjaz
Back to top
View user's profile Send private message Send e-mail
Display posts from previous:   
Post new topic   Reply to topic Moderators: BobTheDog
Page 2 of 2 [45 Posts]
View unread posts
View new posts in the last week
Goto page: Previous 1, 2
Mark the topic unread :: View previous topic :: View next topic
 Forum index » Instruments and Equipment » Strings and things
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