hakonandersson

3-way crossfading with constant power

4 posts in this topic

Hi all,

New member here, so big wave to you all from Melbourne, Australia - thanks for having me.

Now, I need to sound an idea and get some advice/direction from you guys. Using lemur and an iPad, I'm building a production / DJ toolset which I hope to use to help me during production of music stems and 'play' said music in a 'live' capacity. :)

I've been working on a triangular fader between 3 audio sources - effectively it's an equilateral triangle on my screen, and my finger position (the cursor if you will) determines the distance from the 3 verticies of the triangle and from a range of 100 (on the vertex of that channel) to 0 - I've got a linear crossfader of sorts which provides the volume level of each of my 3 channels nicely....

However, as we know - sound doesn't work like that and I won't get a nice constant-power curve as is expected to be used when fading from a > b, for example on a DJ mixer.

Through some investigation online, I've got the trigonometric function which mimics how most constant-power crossfaders work between 2 channels (y=cos((pi*x)/2) if you wanted to know) - but how would I go about introducing a 3rd sound source into this....

Do any of you have any knowledge on managing more than 2 audio sources taking constant power into consideration? Would I simply just apply the same function to the 3rd audio source as I've done with the first two?

Cheers for any help guys!

Hakon.

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So, y gives you the output gain? The equation you're quoting looks like a crossfader curve... but i'm not convinced mathematically it's going to give you the transition you want.

So, are you trying to make like a 3 way mix? Is it something you think could be achieved with three level faders and you're looking to 'simplify' by having the triangle mix area?

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So, y gives you the output gain? The equation you're quoting looks like a crossfader curve... but i'm not convinced mathematically it's going to give you the transition you want.

So, are you trying to make like a 3 way mix? Is it something you think could be achieved with three level faders and you're looking to 'simplify' by having the triangle mix area?

Hey Jester - cheers for the reply.

Yep, y is the output gain, x is the linear distance from '100%' volume on channel x. As you mentioned, I'm trying to simplify the approach (not use 3 level faders) by using the one control area to evenly mix between 3 sound sources - the reason is that I have 3 of these triangles each for Low, Mid and High Frequency Content which is playing stems of music I've produced in those frequency ranges.. aside from the point - I've also got musical key-control over these 3 areas so I can transpose the midi information to tell the instruments to play in an adjacent key for one of the low/mid/high stems...

Therefore, there's a lot going on and one finger controlling 3 levels will be easier than two hands only moving two faders...

I've had a bit more of a think about it - I guess what I'll do is just put a sine wave over all there channels, and just tweak the function (y=cos((pi*x)/2)) so that I roughly get constant power (even if a -3db drop in the middle) cross the equilateral triangle space.

I'll give some feedback here with my results in case anyone else is interested to do something similar... Maybe I'm overcomplicating things.. :)

Cheers,

Hakon.

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The function is a sine wave... well, cosine wave... which is a 180 degree phase shifted sine.

So, you're trying to get all 3 channels at equal gain in the middle of the triangle and more of a source as you move toward a point on the triangle.

You want to sum the three waves to keep a '0dB' gain on the master output, from what i'm reading. I'd try adding a third dimension to the equation/wave: z = sin([sqrt{x^2+y^2}/gain]*2*Pi).

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