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Guitar Audio Filter For Frequency Detection

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by transistance, Jul 8, 2008.

  1. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    No, it has to be an FET, that's the whole point.
     
  2. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The J201 N-channel FET is pretty old (like most guitar circuits) but Digikey still has 881 in stock for $.30US each.

    I would use a 2N5484 FET which has a little more current but should work fine in the simple circuit.

    Many FETs have a current that is much too high and the circuit will need re-design for them to work properly.
     
  3. transistance

    transistance New Member

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    Ok, here is the deal.. I took my circuit to friend of mine with an oscilloscope, he has been an electronic hobbyist since he was 9 and an electronics engineer for about 10 years now. We checked the circuit stage by stage, there is no phase reversal in the circuit, thus no hardware fix needed. The second order harmonic just manages to pass through at lower frequencies and makes the comparator switch states.

    My plan is either to have a low pass filter for each string according to proper bandwidth, or use a second PIC that will do some simple software filtering (e.g. do not stop timer if timer is less then expected value on that string).

    Any simple ideas that might be helpful?? (please no software FFT):)

    or how about switched-capacitor filters??
     
    Last edited: Aug 1, 2008
  4. dave

    Dave New Member

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  5. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    If you check EPE they did a PIC based guitar tuner a couple of years back, and they used a variable filter driven by the PIC.

    I'm presuming this is for a college assignment?, as you can buy far better commercial ones for very little money.
     
  6. transistance

    transistance New Member

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    Nigel it has been longer than 4 months that I am working on this project, if it was for college I would be screwed by now...

    It's a guitar embedded tuner with multiple tuning schemes, according to scheme chosen the PIC will control 6 servos on the headstock of the guitar to tune it to the scheme user input.. if i get it done, it will just be awesome!

    I am in no hurry for a deadline, I'm just impatient by nature... :)

    I have checked the EPE one when I first started the project, i just couldn't make much out of it, I just skimmed through the code (seemed too complicated), didn't see the schematic thus didn't know they had an controlled external filter.. I thought what they did was software filtering.

    I already have a separate tuner and a boss gt-8 multi-fx floor pedal with embedded digital tuner. I'm just doing this because I want to learn something and I like challenge.
     
  7. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Maybe you could add an automatic-gain-control circuit so that the level of the signal to the comparator is just the peaks of the fundamental frequency so that the comparator will not be triggered by harmonics.
     
  8. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Have you built the mechanical hardware yet?, obviously you couldn't use radio control servos for it, as they don't rotate far enough.

    Do you really use different tuning schemes so much?, the usual method is to have two guitars! - my daughter plays bass , and has written various songs that require different tunings, as well as playing covers that do - but she usually just retunes on the last note of the previous song. She has pretty good pitch, and can retune a string as the previous note dies away - pretty impressive to watch. In one of her previous bands the guitarist used to pass her the guitar to tune - it was faster Melissa doing it by ear than using a tuner, even including the time passing the guitar over.

    No, it's external controlled by the PIC - I would suggest you try something similar, and it may be worth buying the back issue(s).
     
  9. transistance

    transistance New Member

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    I have modified sub-micro servos for full rotation before, it will work.

    Yes. I play a wide variety of modern rock, metal and electronic genres.

    You must be proud. When I have a kid, I'm going to make sure he/she is raised as a dedicated and far-better-than-me musician. I started playing when I was 15 (a little late imo); I'm a decent guitar player, and a pretty good electronic music composer. When it comes to perfect pitch for tuning though, I don't have the trained or innate ears for that.

    This project is for the less fortunate like me...

    I think that project is a little ahead of my skills, especially since it has been a long time since i coded any assembly. Maybe, I will look into it when I decide to improve my system.

    Are EPE issues electronic or prints?

    Anyways, here is the latest version of my circuit, it's a little bit more complicated. (Sorry for that...)

    I calculated the ranges of each string in different tunings to develop as little number of filters as possible. I came up with a 3 low-pass filter design that will filter for 2 strings each while attenuating the 2nd and higher order harmonics.

    I greatly appreciate all your inputs,
     

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