odd pedal request - MICROSHIFTING

[nickmaynard]

Hey all, quick question.

I was just asked to include a microshifting feature in a new pedal build. I wasn't entirely familiar with the concept but the idea is, you'd plug a mono signal in, the pedal would split the audio into two channels and send one out dry through one input, while it would shift the other signal by a few milliseconds and slightly detune it before sending it out a second output jack. This is a production technique used to create a much wider stereo sound.

Kinda a neat request but I'm at a loss of how to achieve it. There's essentially several steps to this.

1. Splitting the signal
2. Delay the audio
3. Detuning the audio

Any thoughts? Anyone else ever try to do this with a pedal?

[Keppy]

What you're describing is how a chorus pedal works. The signal is delayed slightly, and the delay is modulated with an LFO to shift the pitch up and down slightly. The difference is, in a chorus pedal the delayed signal is mixed with the dry signal, whereas you want it sent to a separate output.

So, my advice is to pick out a chorus and build it with that modification.

[nickmaynard]

What you're describing is how a chorus pedal works. The signal is delayed slightly, and the delay is modulated with an LFO to shift the pitch up and down slightly. The difference is, in a chorus pedal the delayed signal is mixed with the dry signal, whereas you want it sent to a separate output.

So, my advice is to pick out a chorus and build it with that modification.

wow, because i was coming at it from such an odd angle, i didn't even realize that! thanks!

i could potentially take something this ( http://www.diystompboxes.com/smfforum/index.php?topic=86297.0 ) and remove the lfo / dry wet mix sections and be pretty close to my goal!

[anchovie]

remove the lfo

If you do this, the pitch of the delayed signal won't change.

Check with the end-user whether they are expecting a straight detune or not. If you split a chorus pedal (with LFO intact), you'll get dry signal out of one speaker and slightly-delayed vibrato out of the other. If they don't want the wobble of the vibrato, then a straight detune by a few cents puts you in the realm of digital signal processing.

[Dave W]

flanger. manual (lfo off) mode. put the delay time on a foot pedal. done.  
split the wet & dry for stereo.

[Mark Hammer]

Chorus and flanger pedals produce pitch change by sampling at different rates than they play back.  It's the same thing as recording to tape or vinyl, and playing it back at a different speed than it was recorded at.

The thing is, you can always stick your thumb up against the edge of a turntable or a tape reel, or turndown the motor speed (like this current humorous ad does:  http://www.youtube.com/watch?v=m3B8-PAGkg0 ), and continue to play it slowly or faster, and get a steady pitch change.  And you can do that because the sound is stored in a permanent (vinyl), or stable (tape) fashion.  A BBD only has 1024 storage cells, so it's hanging onto the signal for only a VERY brief period.  Which means that any pitch change can only happen if the "speed" of the chip (i.e., the clock rate driving the chip) is constantly speeding up and slowing down such that the "playback" is always happening at a different rate than the "recording".

That is the long way of saying that achieving a stable pitch shift, so that, let's say, what comes out speaker/amp A is a few cents off what comes out of speaker/amp B, requires a different sort of technology, specifically digital pitch shifting.

If you're fine with one signal being at-pitch, and the other "wobbling" around pitch, then you're good to go with either a modified/split chorus or flanger.  If you were thinking in terms of a constant pitch difference, then something different is required.

[midwayfair]

TH Custom's recording amp has a faux stereo setting:

http://diy.thcustom.com/all-in-one-recordingonstage-unit-diy/

Doesn't involve delay, though. I think it involves a phase adjustment, which, if you think about it, is a lot like what happens when you physically record two speakers that are slightly different distances.

As far as I know, the only way to achieve what the op is talking about is digital.

[duck_arse]

what about a "howl-round stabilizer", like the ETI486? it uses a pair of MC1495 four quadrant multipliers to apply a 5Hz frequency shift to the input signal.

[pinkjimiphoton]

my advice? avoid the little angel pedal. that thing is a mega pain in the ass, and either it doesn't work, or people think it does. they think it does when they can hear "some" difference... which isn't the same as it working (which i could never get it to do more than once or twice, even going thru over 20 2399's.... ) save yourself the hassle, and make something that won't make ya scream in frustration.

[chi_boy]

what about a "howl-round stabilizer", like the ETI486? it uses a pair of MC1495 four quadrant multipliers to apply a 5Hz frequency shift to the input signal.

Where might one find some info on this?  Google and Mouser are not being my friend today.

[R.G.]

The classical double-multiplier frequency shifter uses two Hilbert transform/dome filters to generate a broadband +90 degree phase shift for one version of the input, and another to generate a broadband -90 degrees shift. These are then multiplied and added. There's some trig identities that I'd have to look up that says that you produce a difference of the frequencies.

[duck_arse]

chi, I can scan the project for you if you like.

[chi_boy]

chi, I can scan the project for you if you like.

If it's not too much trouble, the yes, please.

I did find the datasheet for the MC1495.  Looks scary.

[Keppy]

I did find the datasheet for the MC1495.  Looks scary.

And pricy.
http://www.smallbearelec.com/servlet/Detail?no=551

[duck_arse]

here they is:

http://i.imgur.com/cJj7FS6.png
http://i.imgur.com/qW66XbU.png
http://i.imgur.com/NRoHDIs.png
http://i.imgur.com/gMoRNDh.png

[guitarkill]

my advice? avoid the little angel pedal. that thing is a mega pain in the ass, and either it doesn't work, or people think it does. they think it does when they can hear "some" difference... which isn't the same as it working (which i could never get it to do more than once or twice, even going thru over 20 2399's.... ) save yourself the hassle, and make something that won't make ya scream in frustration.

I don't agree. I've built the orginal one and the "birthday edition" and never had problems with either one. Sitck it's quite subte, but it makes a very pleasant sounding not that subtle chorus pedal with a few things tweaked. I like it better than any of the other commercial chorus pedals I've owned.

[kle333]

here it is:
http://i.imgur.com/cJj7FS6.png
http://i.imgur.com/qW66XbU.png
http://i.imgur.com/NRoHDIs.png
http://i.imgur.com/gMoRNDh.png

Thank you for uploading this great project! - I built it 20+ years years ago (!!) and used it with in my busking equipment for decades, while performing to tourists at Sydney's Opera House. I whistle to good music and so, needed a strong whistle tune with less feedback. It also gave my whistle a pleasant type of vibrato swing. Now, I have to build a smaller unit of this "Howlround Stabilizer", which fits into a Mini Demo unit.
It was always my ambition to create a small Demo unit, which has descent bass sound for classical music etc. and an SDcard MP3 player. On eBay I bought such a Mini speaker. It was cheap and sounds amazing for its size: http://www.ebay.com/itm/Mini-Portable-Wooden-Bass-Stereo-FM-Radio-Speaker-MP3-Music-Player-USB-TF-Remote-/291202553087?hash=item43cd0654ff:g:2xYAAOSwxCxT1fGP
I then removed the big handle and filled it with an electret Mic preamp, a Mooer pedal Reverb and a TA2024 2x15W  Amp. - I stripped the Reverb's big sockets etc. so, it all fitted inside this Mini Demo unit. Albeit I placed the whistle speaker about 30 feet away from the Mic, I still got terrible acoustic feedback! The only way to avoid it was to turn down the whistle volume and that's no good!
Solution: There's still room for a small size of this "Howlround Stabilizer". The problem is... that I now got on in age; i.e.turned into an "old bird"!) and need to work with magnifying glass to build a small, compact unit of this "Howlround Stabilizer".
Question: Exist there any way or service to miniaturize this "Howlround Stabilizer" with surface mounted parts?  If there is, it might very costly? If there's, will it be very costly? I would be grateful for good advice on that.
Here are some of my better recording of my whistling to good music:
https://www.mediafire.com/?t0mocnkevh9bz1c
https://app.box.com/s/6f72eb90c2002db2e9fc
https://app.box.com/s/bluoxacemqlslhtq9bv9
https://app.box.com/s/sbfb81jzjspnalv2ipad
https://app.box.com/s/y8s8jdqbxibdbo813x22ftborzdnqmy7
http://www.youtube.com/watch?v=KPEW8KdBxds
https://www.mediafire.com/?bfb7fhexdob4ztj
More fun... at:  jdrinda.tripod.com
Please use copy/past if link fails to open...  Thx, Joh

[Rixen]

what about a "howl-round stabilizer", like the ETI486? it uses a pair of MC1495 four quadrant multipliers to apply a 5Hz frequency shift to the input signal.

it also shifts the signal harmonics by 5Hz resulting in them no longer harmonically related to the fundamental.. OK for speech, but maybe not so great for an instrument.

[duck_arse]

hey kle333, always good to be welcoming another cobber, especially a whistling one. you don't do gum leaves as well, by chance?

a quik googoo shows futurlec stocks the dil MC1495 (oddly), and the ON semiconductor datasheet shows they come in a surface mount version. I don't know if that is any help to you tho. there must be a half dozen modern ways to do what you want, you just need to find them.

[kle333]

hey kle333, always good to be welcoming another cobber, especially a whistling one. you don't do gum leaves as well, by chance?
a quik googoo shows futurlec stocks the dil MC1495 (oddly), and the ON semiconductor datasheet shows they come in a surface mount version. I don't know if that is any help to you tho. there must be a half dozen modern ways to do what you want, you just need to find them.

Thanks for the reply! Yes, I'm excited about this circuit, because it really works great and doesn't cut down on any frequencies, unlike other feedback eliminators/ killers. To build it again in small format will be quite hard for me to do, but I can do it without PCB, by just soldering one part onto the other. That way I can compact its size. I bought a couple tiny Chinese converter modules, which turn +12VDC into dual rails +/- 15V.  I already bought 5 of these MC1495 for only $US7.40 the lot, incl. ship. I wished there would be an easier way of miniaturizing this circuit.

"...you don't do gum leaves as well, by chance?": No, I just whistle naturally with my tongue & lips. When I was young and handsome (sadly, now only the latter) I often whistled up to 13 hours non-stop. But then, in the train on the way home, I felt heavy ...like a sack of potatoes!