Phase alignment circuit discussion please.

[Svart]

We need to come up with a phase alignment circuit as a group project. I was looking at the Little Labs IBP but 600$ is a little more than I had expected for this by far.

Anyone have the first idea to bring to the table?

 

[Svart]

http://users.ece.gatech.edu/~mleach/ece4435/f02/dp3.pdf

 

[the scum]

That GA tech one looks a lot like one stage of an MXR phase 90.

There's also this one, which removes the voltage control:
http://www.forsselltech.com/LF Phase Test.pdf

For static phase shifts, I think that's the circuit you want.

 

[hejsan]

Does anyone know what this MCCurdy line/mic pre can do?
http://cgi.ebay.com/Mccurdy-preamp-...QQihZ004QQcategoryZ119022QQrdZ1QQcmdZViewItem

It has a variable phase it seems..

hejsan

 

[Svart]

I'm interested in something adjustable for sure.

more on this later.. :green:

http://www.edn.com/archives/1996/021596/04di4.htm

http://sound.westhost.com/project103.htm

http://pdfserv.maxim-ic.com/en/an/AN559.pdf

 

[JohnRoberts]

[quote author="Svart"]We need to come up with a phase alignment circuit as a group project. I was looking at the Little Labs IBP but 600$ is a little more than I had expected for this by far.

Anyone have the first idea to bring to the table?[/quote]

The IBP is probably a glorified version of the simple opamp circuit you provided multiple links to. Yes you should be able to cover the phase shift for a few $.

I question whether this 180' phase shift circuit, with adjustable frequency, mimics some natural function and would work as the IBP FAB suggests. It seems it coiuld only correct one note for a given adjustment. If you are getting cancellation from multiple open mics the fix IMO is delay to time align the sundry waveforms, not phase shift.

This simple circuit is the heart of guitar phasors (not flangers) so perhaps useful as an effect.

JR

 

[Mendelt]

There's a circuit on page 77 and 78 of the art of electronics that might be usefull. I cant get any schematics uploaded right now but maybe someone else can look it up

 

[SSLtech]

John,

I completely agree.

If you want to read how confused people can get, try this thread:
http://recforums.prosoundweb.com/index.php/t/13833/2172/

In the end I ducked out, since people just don't understand...

Keith

 

[enthalpystudios]

i just read that entire psw thread, and thanks for pointing it out... it was to tough to decipher all the lingo and info within, but (with a little faith in keef-posts) i believe I've got a clearer picture than I had previously had.

so thanks for that link...

 

[Mendelt]

Would something like this work? R6 should be variable to change the phase of the output signal.
Of course this can be improved.. :grin:

 

[clintrubber]

[quote author="Mendelt"]

Would something like this work? R6 should be variable to change the phase of the output signal.
Of course this can be improved.. :grin:[/quote]
That's a suited topology. Keep R1 & R5 small w.r.t. the impedances of C1 & R6 and load the output with a Hi-Z.

The opamp-topology might be easier (where the R&C doing the work are at the input i.s.o. at the output).

More good info:
http://www.geofex.com/Article_Folders/phasers/phase.html

Bye,

Peter

 

[PRR]

> The IBP is probably a glorified version of the simple opamp circuit

Not terribly glorified:

http://www.littlelabs.com/ibp.html

http://www.littlelabs.com/IBPMAN.pdf

BTW, our host sells the IBP and IBP Jr. And not for $600.

Little Labs should not be losing big money on production at $600, or even at Prodigy Pro's price. But they won't get filthy rich either. And I wonder, by the time you figure out the parameters, all the switchery, add the good input and outputs, all in a nice sturdy case, if you can touch $500 without admitting that your time is nearly worthless.

 

[Svart]

Even at PPro's price I still can't justify the purchase, I have much bigger fish to fry for 300-600$.

But just purchasing it does little for the learning process other than cracking it open to have a look.

So a phase align circuit tends to only align certain freqs, so what would/could we do to do this in another way?

How about chained opamp buffers and switching them in/out of the chain to raise/lower the time delay between input and output? It would be too fast for normal delay usage but it could be useful for uS delays between the moving coil and the DI..

 

[JohnRoberts]

[quote author="Svart"]Even at PPro's price I still can't justify the purchase, I have much bigger fish to fry for 300-600$.

But just purchasing it does little for the learning process other than cracking it open to have a look.

So a phase align circuit tends to only align certain freqs, so what would/could we do to do this in another way?

How about chained opamp buffers and switching them in/out of the chain to raise/lower the time delay between input and output? It would be too fast for normal delay usage but it could be useful for uS delays between the moving coil and the DI..[/quote]

Rather than speculating how to do the same as, perhaps you could describe the problem or shortcoming you are trying to correct?

JR

 

[Svart]

ok, I suppose the easiest way to explain is compensating for the latency of the system of amp-speaker-air-mic VS. a DI box to align the DI and the mic in time, not just at certain freqs.

 

[NewYorkDave]

If you need a broadband linear delay, then... why not just use a digital delay? Some of them are even settable in feet or meters instead of mS. This is one instance where doing it properly in the analog domain is probably more trouble than it's worth.

If it must be analog, there are always BBD devices (poor fidelity, OK as an effect) or perhaps even tape, if you have control over head spacing and a wide range of vari-speed.

 

[JohnRoberts]

[quote author="Svart"]ok, I suppose the easiest way to explain is compensating for the latency of the system of amp-speaker-air-mic VS. a DI box to align the DI and the mic in time, not just at certain freqs.[/quote]

If trying to compensate for an air path length transit time, vs. electrical transit time the problem is pure time delay.

In digital domain it should be no big deal to add some delay offset to the direct channel to line them up with the later arrival.

To make a free standing (digital) delay purely for that purpose is probably a little harder and more costly (than phase shift), but not out of the question for this group.

FWIW, if the air path is short (a foot or so) the time delay is well within Haas fusion region and transient events will be fused together as one, while the wavelengths where cancellations can occur only affect higher frequencies. Longer air path lengths will drop the frequency lower where cancellations can occur.

Different mic placement is cheaper than adding delay compensation.

JR

 

[JohnRoberts]

[quote author="NewYorkDave"]If you need a broadband linear delay, then... why not just use a digital delay? Some of them are even settable in feet or meters instead of mS. This is one instance where doing it properly in the analog domain is probably more trouble than it's worth.

If it must be analog, there are always BBD devices (poor fidelity, OK as an effect) or perhaps even tape, if you have control over head spacing and a wide range of vari-speed.[/quote]

I did a lot of work with analog delay (BBD & CCD) back in '70s and early '80s. IMO at their best they lack the bandwidth and dynamic range to be useful for anything other than effects.

Digital delay OTOH is arguably as good as conversion portals.

JR

 

[clintrubber]

FWIW, has the Portico Duo Mic Pre/ Variable Phase DI
Portico™ 5016 been mentioned yet ?

Has a phase-thingy as well:

Vari-Phase
Rotates the phase of the DI channel. This allows a user to combine signals without cancellations or use phase cancellations to create new sounds

 

[JohnRoberts]

[quote author="clintrubber"]FWIW, has the Portico Duo Mic Pre/ Variable Phase DI
Portico™ 5016 been mentioned yet ?



Has a phase-thingy as well:

Vari-Phase
Rotates the phase of the DI channel. This allows a user to combine signals without cancellations or use phase cancellations to create new sounds

[/quote]

and they still spell bus wrong,,,

In a product with another feature labelled "silk" I suspect the perceived value to potential customers exceeds the cost of one opamp and one potentiometer. So it is probably good "merchandising" and good business. I remain unconvinced that it is a useful feature, but it's cheap enough to make one and decide for yourself. It will make the sound different, I'll grant it that.

JR