"guitar signal" generator

[the_guvnor]

first post, baby.  i hope it's not a dumb question.

i'd like to make a box to generate something that could pass for a sustaining guitar signal (as far as envelope is concerned) that could be processed further by a tremolo circuit and such.

the only requirement is that a standard envelope following input on a guitar effect could track it, both by itself and if processed by a tremolo or other amplitude-altering effect.  if that would work i suppose frequency content is arbitrary.

i'm talking about making a little box, not just using a lab signal generator (which i don't want to strap onto the pedalboard ).  any ideas on how to do this?  i was looking at some simple noise generating circuits.  i figured the output could be compressed or filtered as necessary and maybe do the trick.

thanks guys.

[aron]

My first thought is something digital like a sampler. Is it just that you want to play back a sustaining guitar signal?

[toneman]

well, a "sustained guitar signal" is close to a sine wave.
Note: this is a pure guitar signal--no effects--after the plucking,
the string vibrations look like a sine wave on a scope.
it's the plucked attack/decay envelope that emparts much of the
guitar" characterstic.  
If U R looking for a signal injector, then thats an oscillator.
A guitar is an oscillator that has it's own unique envelope.
Add an enevlope generator and an envelope amplifier
and U have a "synthesized guitar".
Well, U actually have the building blocks for a modular synthesizer.
Depends on what U want 2 do with the signal.
If U are working on a fundamental extractor, varying the amplitude
is really all U need 2 determine lock in/hold thresholds.
If it's just one frequency U need, a 555squarewave generator
with a LowPassFilter(LPF) to filter the sine from the square is
really all U need.  Then adjust the amplitude with a pot.
staylocked
tone

[DDD]

IMO such a generator should provide actual (or very close) guitar signal envelope. Otherwise it will be nothing but a piece of junk or simple time\money loss.
...very interesting subject by the way...

[The Tone God]

Normally I use a signal generator but sometimes I record guitar stuff in my computer, convert it to MP3, then drop it into my MP3 player which I then feed the box with. Otherwise I play with the output of my generator or just plug a guitar into the box.

Andrew

[the_guvnor]

those are some good ideas.  it seems like a digital sampler or MP3 player would work.  i'll look into a simple oscillator too, which may be what i end up doing if it's simple enough because i'd like a dedicated box with some processing on board.

i may have confused some people before, but what i was looking for is what might act as a signal from a theoretical ever-sustaining guitar note, that is: not to emulate the attack/decay characteristics of a guitar.  i want it because i have a box on which an input can be used for just reading the envelope and processing a different signal based on that.  my goal is to have something like LFO control when i use the tone generator with a tremolo circuit behind it fed into the envelope following input.  the signal could sound like a clarinet or noise for all i care, because it will never be heard.

so, i guess just playing a sampler or an MP3 player into a tremolo would probably work until i build a box for it.

[the_guvnor]

where could i find some relevant schematics anyway (simple oscillators, etc.)?  i found a couple here and there.

[col]

I built a tone generator on stripboard from R A Penfolds book "Electronic music effects". It was based on a 555 chip and has several modes and  can produce tones over several octaves. I also built a distortion switch into it. If I can find the layout sketch I drew before I built it I will copy it into the computer and post it here.

Col

[DDD]

I think that the best way to simulate the signal including its attack\sustain\decay (and maybe with some overtones that guitar actually has) is to use PIC-processor.
Too complicated? But it seems there are no simple methods.

[Mark Hammer]

There's an old project that appeared in Polyphony magazine at my site called the "Alpha Drum".  It was intended to be used for simple sampled percussion modules.  Essentially, sample a drum, trim/shape the file, and burn it into an EPROM where it gets treated like a wavetable and streamed out whenever a trigger pulse is received.

Absolutely no reason on earth why the sample couldn't be a standardized guitar signal, providing suitable signal level, timbre, attack and dynamics for benchtesting a circuit.  Build the thing into a box, set it up with a calibrated output level, and press a momentary switch to initiate an output every time you need to do things like check impulse handling, or filtering, etc.

The board (layout is provided, but you'll probably have to flip it for PnP) is actually pretty compact and doesn't require a fortune in parts, so you can even keep a couple of standard sounds on tap in different modules.  Available at:  http://hammer.ampage.org

Alternatively, get a cheap Yamaha or Casio sampled keyboard at a yard sale or 2nd hand shop, and use their sampled percussive/plucked sounds to put your circuits through their paces.

[dr]

....when I bench test something I build, I have a CD player with an attenuator connected to the output,to drop the signal down to about the level of signal that my guitar puts out (I don't like taking my '59 Strat down to the cold damp concrete basement) and put in a self-made CD that has all the sounds I could wrench out of it (meaning I've recorded the Strat without effects of course) into whatever I'm testing-that out into the shittiest sounding solid state amp I own; and when it starts sounding good, I go back upstairs and plug that pedal  AND the REAL Strat (which is where the Strat resides) into my "favorite amps".....if it passes that test,I'm happy and the pedal or whatever is half done. THEN I take it out to the gig....... Mark!...did you get my e-mail about the Reticon info?.......dr

[bwanasonic]

I think I still may be confused on what the intended purpose is, but I used to use the *sound out* on my Korg DT-1 tuner as an oscillator that I would process in various ways. It comes in handy as a portable little *test tone* as well. And of course it doubles a tuner! :wink:

Kerry M

[Samuel]

i have also used my guitar with an ebow - lay the guitar flat and sit the ebow on the strings - as a signal generator. yeah it costs $90 or w/e, but hey then you've got an eBow

[Gilles C]

A CD or MD player, with the following circuit added:

http://www.muzique.com/lab/pickups.htm

Arg... I re-read it again, and my new suggestion is the Boss Feedbacker circuit

You could take only the feedback portion of the pedal

[zachary vex]

i just built a little twin-t oscillator that puts out around 200 mV at around 400 Hz.  minimal parts, minimal power consumption, and a nice clean sine wave.  it doesn't have any "envelope" but it will sustain indefinitely.  it's possible to tweek the gain on such a circuit and make a touch-point to trigger it with your finger, and get attack and decay too, using perhaps one or two more components.

i nabbed mine from the electronic music chapter in john markus' book "electronic circuits manual" and i believe it was copied from wireless world in the 60's, but there are tons of resources online for designing twin-t "bongo" circuits.

[Transmogrifox]

From what it sounds like you're doing, a simple oscillator is all you need.  I think I know what you're doing, because I'm doing a similar thing with the envelope filter I have built (in debugging mode right now)--

It has an oscillator output and then the envelope follower section has an external input that can be AC or DC coupled to anything. My thinking is that I can put the oscillator through a tremolo (like you were thinking), or wah pedal to make the rich variety of filter tones available to pedal control, or even choruses and flangers, then return the output to the envelope follower input.  I would recommend an oscillator frequency of about 2.5 kHz--square wave, so there's more power in the signal for processing.

Check out some of the LM555 timer app notes.  I'm sure if you keep looking, you'll find an oscillator based on the 555 that you can cannibalize for your purpose.  Use the CMOS 555 as it is a little lower power consumption, less current draw so it won't hack up your power supply and inject a high-pitched annoying signal into your signal path.

[the_guvnor]

Nice!  I found a few twin-t ciruits that are, indeed, simple and easy (ah, and there are two "T"s in there... that's what it's from ).  I'll pick up a couple of 555s and try that out, too.  Either way, this should be easier than I thought.  And they both can be made to run on +9v, which is righteously awesome.

[zachary vex]

you can usually sub a 2n5088 or MPSA18 for most any transistor in a twin-t circuit.