String pluck detector??

[col]

I don't understand the electronics of it but Penfold uses one a lot for his circuits in the Babani books based on an LM13700/13600 for triggering autowahs, tremelos etc. Might be of some use.

[markusw]

I don't understand the electronics of it but Penfold uses one a lot for his circuits in the Babani books based on an LM13700/13600 for triggering autowahs, tremelos etc. Might be of some use.

Thanks! 
I'll have a look...

Markus

[gez]

Interestingly, the PLL locks in faster when the strings are plucked a bit harder although the guitar signal squarer works at much lower levels. Also performance is better when the strings are plucked with a pick. Since I never used a pick with bass the clip is also done without. It's a cheap Strat copy at neck pu and recording was done directly into the PC w/o cab sim.

Presumably the squarer is just an op-amp comparator?  If so, try feeding its output to the input of a schmidtt trigger Logic chip (40106 or similar) to clean it up, or - Unless you're likely to use the other devices in the package - you can even wire up a CMOS555 as a schmidtt trigger (takes up less space on a PCB).

[markusw]

Presumably the squarer is just an op-amp comparator?  If so, try feeding its output to the input of a schmidtt trigger Logic chip (40106 or similar) to clean it up, or - Unless you're likely to use the other devices in the package - you can even wire up a CMOS555 as a schmidtt trigger (takes up less space on a PCB).

Hey Gez,

thanks for the tip! It's a LM311 followed by a 4070 XOR gate (because I have it on breadboard). Do you think the 4070 is OK or would you use another one to clean it up?
The XOR is connected with one input directly to the LM311's out and with the other input to Vref. I also have some spare 4049 stages on breadboard. Would you prefer them over the 4070?

Markus

[gez]

Presumably the squarer is just an op-amp comparator?  If so, try feeding its output to the input of a schmidtt trigger Logic chip (40106 or similar) to clean it up, or - Unless you're likely to use the other devices in the package - you can even wire up a CMOS555 as a schmidtt trigger (takes up less space on a PCB).

Hey Gez,

thanks for the tip! It's a LM311 followed by a 4070 XOR gate (because I have it on breadboard). Do you think the 4070 is OK or would you use another one to clean it up?
The XOR is connected with one input directly to the LM311's out and with the other input to Vref. I also have some spare 4049 stages on breadboard. Would you prefer them over the 4070?

Markus

My experience of constructing oscillators using the 4070 (or using them as buffers) then trying to use their outputs to clock flip-flops says that they're not such a good choice.  I still say use a dedicated Schmidtt device - they're designed to give clean switching at 'fast' speeds (an audio signal isn't that fast) and I've found that it really makes a difference when driving PLLs (lock-on time is much quicker).  Also helps if you square the crap out of the signal before going to your comparator.  Diode clipper circuits with plenty of gain are ideal for this.

[markusw]

Hey Gez,

will give ot a try. Would one ore to 4049 stages be OK??

Here btw is a draft schem: http://www.aronnelson.com/DIYFiles/up/PLL_AMS100_PD_NE555_current_sch.pdf
The input stage, lp filter and the first part of the AMS-100 PD is not shown. All opamps are TL072,4.
U8 and U9 simulate a LF398

Markus
.

[StephenGiles]

Please forgive me but I still cannot grasp what you are trying to achieve.

I would like to reliably get a pulse each time I plug a string. It should also work for fast runs and if notes are played legato. Of course hammer-ons would be cool too 
Actually, I don't need an envelope, only if it's part of the pluck detector.

Regards,

Markus

I see, I'll look at the Arp Avatar manual over the weekend for anything that may be of help.

Couldn't see anythng of interest.

[gez]

Hey Gez,

will give ot a try. Would one ore to 4049 stages be OK??

Here btw is a draft schem: http://www.aronnelson.com/DIYFiles/up/PLL_AMS100_PD_NE555_current_sch.pdf
The input stage, lp filter and the first part of the AMS-100 PD is not shown. All opamps are TL072,4.
U8 and U9 simulate a LF398

Markus
.

Haven't looked thru your preliminary schematic yet Markus, but look forward to perusing it at my leisure (probably over the weekend).

My preference when it comes to Schmidtt devices is the 40106 or 4093, though if you wire pins 2&6 together of a 555 and use pin 3 as the output it takes up less space and works just as well.

4049?  Never used them for Schmidtts.  If I were to use them, I'd wire two in series so that the output is non-inverting, then I'd wire up a resistor (100k say) from the output of the squarer to the input of the first inverter, and then another resistor (equal in value) from the output of the second inverter to the input of the first.  It's a common arrangement and you should be able to find a schematic on-line for it, though I have no idea how well it will perform. 

Although one of the inputs of a 4046 (haven't checked, but presumably you're using it?) can accept signals that are less than perfect, the cleaner the signal to this input the better the PLL behaves: less work for it to do (as it were).  For this reason, I've found that logic buffers with schmidtt inputs really make a difference in terms of tracking etc.

[markusw]

Hey Gez,

thanks a lot for your explanations!  Will give it a try for sure!

I found two bugs in the schemo. The file is updated.

Markus

[markusw]

One more Q: is the propagation delay the parameter that determines whether a device is suitable for cleaning up the signal?

Although one of the inputs of a 4046 (haven't checked, but presumably you're using it?) can accept signals that are less than perfect,

Forgot before: I'm using phase comp 2 which is supposed to be less immune to noise than PC1 but it can't lock in on harmonics.

Edit: I found a 4093 

Markus

[markusw]

Please forgive me but I still cannot grasp what you are trying to achieve.

I would like to reliably get a pulse each time I plug a string. It should also work for fast runs and if notes are played legato. Of course hammer-ons would be cool too 
Actually, I don't need an envelope, only if it's part of the pluck detector.

Regards,

Markus

I see, I'll look at the Arp Avatar manual over the weekend for anything that may be of help.

Couldn't see anythng of interest.

Nevertheless, thanks!! 

[gez]

One more Q: is the propagation delay the parameter that determines whether a device is suitable for cleaning up the signal?

More important (IMO) is the following:

http://en.wikipedia.org/wiki/Transition_time

All helps though.

[gez]

It's interesting that you have both inputs of the LM311 biased to Vref.  I do something similar quite often using CMOS output amps and in their quiescent state, the outputs actually try to bias to half supply - though they're far from stable and swing all over the place - and the chips have a tendency to act as an amplifiers towards the tail end of notes, rather than comparators.  Because there's no negative feedback, the signal is always clipped, but the sides lean inwards as a signal decays.  This gives the effect of introducing dynamics - not in terms of amplitude but 'timbral' dynamics.  The end result makes for a more interesting comparator fuzz, but the signal needs cleaning up to be suitable for, say, driving the clock input of a flip-flop, which is why I use Schmidtt trigger buffers.

Do you own a scope?  I'd love to know if something similar happens with these chips (just play a note and watch the slope of the square output as the note decays).  Just curious.   

[markusw]

More important (IMO) is the following:

http://en.wikipedia.org/wiki/Transition_time

All helps though.

Thanks! 
I compared the data sheets for the 4070 and the 4093 and it seems that transition times are identical between the two. Nevertheless, I will try to free some space on my breadboard to compare their performance.

It's interesting that you have both inputs of the LM311 biased to Vref.  I do something similar quite often using CMOS output amps and in their quiescent state, the outputs actually try to bias to half supply - though they're far from stable and swing all over the place - and the chips have a tendency to act as an amplifiers towards the tail end of notes, rather than comparators.  Because there's no negative feedback, the signal is always clipped, but the sides lean inwards as a signal decays.  This gives the effect of introducing dynamics - not in terms of amplitude but 'timbral' dynamics.  The end result makes for a more interesting comparator fuzz, but the signal needs cleaning up to be suitable for, say, driving the clock input of a flip-flop, which is why I use Schmidtt trigger buffers.

Do you own a scope?  I'd love to know if something similar happens with these chips (just play a note and watch the slope of the square output as the note decays).  Just curious.   

I only have a software scope I use with my USB audio interface but I will check. Do you think that wiring the LM311 this way might be not optimal for squaring (the squared signal is fed into the PLL only for about 100 ms following each pluck)?

Markus

[gez]

More important (IMO) is the following:

http://en.wikipedia.org/wiki/Transition_time

All helps though.

Thanks! 
I compared the data sheets for the 4070 and the 4093 and it seems that transition times are identical between the two. Nevertheless, I will try to free some space on my breadboard to compare their performance.

It's interesting that you have both inputs of the LM311 biased to Vref.  I do something similar quite often using CMOS output amps and in their quiescent state, the outputs actually try to bias to half supply - though they're far from stable and swing all over the place - and the chips have a tendency to act as an amplifiers towards the tail end of notes, rather than comparators.  Because there's no negative feedback, the signal is always clipped, but the sides lean inwards as a signal decays.  This gives the effect of introducing dynamics - not in terms of amplitude but 'timbral' dynamics.  The end result makes for a more interesting comparator fuzz, but the signal needs cleaning up to be suitable for, say, driving the clock input of a flip-flop, which is why I use Schmidtt trigger buffers.

Do you own a scope?  I'd love to know if something similar happens with these chips (just play a note and watch the slope of the square output as the note decays).  Just curious.   

I only have a software scope I use with my USB audio interface but I will check. Do you think that wiring the LM311 this way might be not optimal for squaring (the squared signal is fed into the PLL only for about 100 ms following each pluck)?

Markus

Only way to tell is by scoping it to see...or make a comparison and use you ears. 

Same with the 4070 vs 4093 (data sheets schmata sheets)

[markusw]

Only way to tell is by scoping it to see...or make a comparison and use you ears. 

Same with the 4070 vs 4093 (data sheets schmata sheets)

Will check it out.....

Markus

[markusw]

Just did a few corrections and added the LED indicators in the schem. The file in the link above is updated.
Some more comments:
Values for R3, R4, R21, R14 and R15 are estimations of trim pot settings
R21 is a 100k plus a 10k in series. A multi-turn pot would probably be a good idea. It seems that the minimum sampling time required to achieve reliable lock-in with each pluck can be tweaked for a couple of ms.

Suggestions for improvments are highly appreciated.

The comparator around U6 I suppose could be skipped by just swapping the connections to the inputs of U7.

Markus

[markusw]

Here's another short sample. This time it's just the PLL two octaves up w/o the Ring Mod and on the other channel (as suggested by toneman  ) the clean guitar signal.
http://www.aronnelson.com/DIYFiles/up/PLL_SH_2_octaves_up_2_18-03-07.mp3

Do you think that the glitch at the beginning of each note is tolerable?

Edit: Again I didn't use a pick because I never use it. For any reason however, lock-in is faster with a pick. Don't know why. Probably, the squared signal is somehow "purer" immediately after a pluck if a pick is used and therefor the PLL locks in faster?. Any ideas??

Regards,

Markus

[slacker]

Cool stuff, I've been looking into pluck detectors recently to use with a ADSR controlled filter experiment.
Yours looks interesting, probably overkill for what I need though.
The sample sounds cool, the glitch at the start of the notes is fine by me 

[MR COFFEE]

Markus,

Do you think that the glitch at the beginning of each note is tolerable?

I presume you are planning to feed this into some kind of synthy gizmo with an ADSR or at least A-R controlling a filter and envelope?

Lots of real world sounds have a glitch on the attack that gives it character. Synthesists used to put a little short burst of noise or other quasi-harmonically-related something on the start of Sax patches to simulate the way a real saxaphone attack sounds. Fed through the filter, it sounded pretty convincing - at least for the days before samplers came along. I think your glitch will do admirably. Could sound like a micromoog.

Your pluck detector can do double duty triggering the ADSR generator for the synth modules. Got any old SSM or CEM chips laying around? Or you can do discrete if you don't mind all the components. Could be a really cool and unique gizmo.

The VCO tracking is much better than I had anticipated - especially with the bass input. Craig Anderton would be proud. Move over AMS-100. New kid's in town

Keep up the good work and keep us posted.