diy/cheap variable phase control

[paulneedles]

i was reading a review of the tfpro p10 twin recording channel, and although i don't really need more pres, eqs or compressors, i was intrigued by the variable phase control, which allows the phase of a signal to be moved through 180 degrees. i thought this would be handy for rescuing dodgy drum phase and for no headphones/all in the same room recording. How easy would it be to build such a circuit, to be used on an unbalanced insert point? or is there anything cheap that will do 4 or 8 channels?

[DeeDrive]

why not just correct it manually in your DAW after the fact? This would usually be easier than doing it on the fly anyway, plus you have the advantage of visually lining things up on the screen. I'm guessing any circuitry that could do this would probably be detrimental to the signal.

[paulneedles]

i'm using a reel-to-reel, so that's kind of out. probably should have mentioned that in the original post!

[DeeDrive]

ahh..I see, I would maybe look into an IC that has a variable delay, cus that's all a phase shifter would do....

[tINY]

actually, a "phase shifter" would be an all pass filter. But these only really correct the phase for a narrow band,

I Believe there is one from Gyraf available....



-tINY

[Jim Williams]

Yes, it's a classic all pass filter, or phase shifter. One can make one out of a couple of c's and r's with a decent opamp. Use a dual 10k or 100k reverse log pot for the r's to make the phase adjustable. See opamp cookbooks or Don Lancaster's opamp filter cookbook.

Jim Williams
Audio Upgrades

[Ethan Winer]

Paul,

> i was intrigued by the variable phase control, which allows the phase of a signal to be moved through 180 degrees. i thought this would be handy for rescuing dodgy drum phase and for no headphones/all in the same room recording. How easy would it be to build such a circuit, to be used on an unbalanced insert point? <

I'm not sure a phase shifter will do what you want, but if you want to build one there are plans in this article on my personal site:

www.ethanwiner.com/St-Synth.html

This project is a stereo synthesizer, but removing one connection turns it into a six-stage all-pass filter.

That connection is the buffered input signal going through the 47k resistor to either the A or B output. Let me know if you need more clarification.

--Ethan

[paulneedles]

thanks a lot for this - i'll let you know if it achieves the desired effect. and if it doesn't, i'll still get a cool stereo phaser. great website by the way!