A Matrix-Based Pan Pot With Variable Width

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mediatechnology
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A Matrix-Based Pan Pot With Variable Width

Post by mediatechnology »

This one uses a sum-difference matrix using the THAT1240. It is not a constant power panner but is instead constant voltage mono sum. It's pretty smooth.

An interesting thing is that the insert can be used to introduce a frequency or time-dependent element while a perfect mono sum is still maintained. Things go in mono, come out stereo with some width, and then fold back down to mono without phase cancellation.

Image

I did a demo here where I just used a cap in the insert. The original source is mono but you can hear a frequency dependent slightly left-heavy pan. LF is mono with progressively increasing width at about 11:00.

https://www.ka-electronics.com/content/Panner_Demo.mp3 (4.3 MB file size)
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XAUDIA
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Re: A Matrix-Based Pan Pot With Variable Width

Post by XAUDIA »

So, if I'm understanding this properly, this can send the lower frequency content down the middle, and then at some frequency defined by the cap (or eq circuit insert), the signal goes increasingly to the position set by the pan pot?

A mix technique I sometimes use is to split a stereo signal into two buses, LPF one bus and make mono, and then HPF the other at the same frequency and pan out hard left and right. This helps keep some bass under control but keeps some top end sparkle.
One thing I always wanted was a simple stereo box with just a frequency control that would do this for me, without phase shift problems. It looks like a pair of the above could be used for this.

Nice! Thanks!
New music at xaudia.com
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mediatechnology
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Re: A Matrix-Based Pan Pot With Variable Width

Post by mediatechnology »

Thank you for your reply.

You are correct. Your example (and the demo) have a high pass filter in the insert so the image collapses to mono as the frequency lowers.

Other insert options could use dynamics processing so the signal widens vs. level. Time delay, reverb etc could also be used. The "effect" goes away when the output gets folded down to mono. That could be an advantage or disadvantage.

On a circuit design note one could easily argue for a coupling cap between the wiper of the pot and the junction of the 22Ks. There is some DC bias current in there, about 900 nA, and the 22Ks provide a DC path for that bias current during rotation. They do provide an improvement in feel as well broadening the center.
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