360 Degree, 4 Ch. Audio Panner

Suggest you post in one of the rec.audio NGs

What kind of hearing model are you assuming ?

Just simple amplitude weighting ?

Or perhaps correct phase and/or time delay relation ship between the channels ? The criticality also depends on frequency. You might get away with a simple model on some frequencies, but not on other.

In human hearing, the shape of the external ear will modify the frequency response of sounds coming from different directions.

How believable should the hearing experience be ?

One could do the cheesy thing, put four speakers in an anechoic box with a rotating array of four microphones...

Or you could drive four quadrants of a 360 degree potentiometer (this will have some amplitude variation). Scratchy potentiometers aren't recommended.

Or, you can note that an interpolation rule can give the in-between signal in amplitude-independent form,

Soutput(theta) =3D Sinput(0) *A+ Sinput(90) * B + Sinput(180) *C + Sinput(270) * D

where A is zero unless theta is in the (270,,,90) range, or cos**2(theta) when it's in that range. B is zero unless theta is in the (0...180) range, otherwise sin**2(theta) C is zero unless theta is in the (90...270) range, otherwise cos**2(theta) D is zero unless theta is in the (180... 0) range, otherwise sin**2(theta)

Four multiplying DACs and a oscillator/counter/lookup-table will do it (and maybe some logic to enforce the zero terms with an analog switch).

OOPS. It's a mono signal? You'd only need two DACs, one for sin**2 and one for cos**2... still need analog switches to steer on a quadrant-by-quadrant basis, though. Multiplying converters are very useful, here; they take the AC signal as the reference, and output the product of that reference and the (nonnegative) digital value you feed them.

Nothing exotic. I just want a uniform rotational effect from speaker- to-speaker that is independent of frequency.

Analogous to a bounce between L and R channels (there are plenty of circuits and music products for this), but circular.

Greg Hanson

Three panners/electric attenuators?

mono -> left, right left -> front left, rear left right -> front right, rear right

You'll need a sine wave generator with a 90 degree shifted output to produce a circle. There should be some schematics on the web. If that's too hard, two unsynchronized sine waves will produce Lissajous patterns. They spin too but not in a circle.

Panning is a subtle effect. The old analog way to do this is a speaker mounted under rotating horns. This produces the phase changes, doppler shift, and reverb needed for a strong spinning effect. Professional music software can simulate it.

Quad pan pots as they were called were common on pro audio mixers in the

Cheers

Ian

For that, all you need are four ganged pots, with a 90 degree dead zone, set 90 degrees apart...

Charlie

But, it has to move at up to 40 Hz rotation rate? That bunch of pots will wear out fast. Either a capacitive or inductive solution would work better, longer. And there's the small matter of driving the shaft according to some (yet unspecified) rule of position-versus-time.

Actually, if I had to do this, I would use four digital pots and a micro, to do the logic of what the different pot settings needed to be. No wear or tear then...

Charlie

Sort of a solid-state Leslie effect?

--- news://freenews.netfront.net/ - complaints: snipped-for-privacy@netfront.net ---