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Making stereo out of mono

Making stereo out of mono

Postby fbjon » Sun Mar 15, 2009 11:35 am

In that "Here we stand" song for the Immortal Empire compo, I have two violin parts (i.e. at the same time, not the first and the later), both recorded with the same mono mic. I figured out a few nice tricks to make one sound as a solo part, with the other backing, that I thought I'd share someplace.

First, I deliberately used an instrument with a softer and darker tone for the backing, I expect this would apply to just about anything. I also put some EQ on both parts to exaggerate the bright/dark contrast. Next, one is panned left and the other right (not hard), in this case the backing part is on the left, which is important for the next step. I put a delay on the backing part only, and set feedbacks to zero, and the left delay to minimum. Naturally, you need to mute the source pass-through as well. The right delay can then be adjusted between ~20-50 msec to simulate room reflection. Finally, some matching reverb to gel it all together.

Getting it to sound good takes a bit of tweaking the milliseconds, panning, and levels, I think precise values would depend on the source material, because some frequencies will start to sound strange at some values. It's no convolution reverb or room simulator, but it's quick and dirty, and gives a feeling of space from a mono signal.

What I actually wanted at first was to simulate binaural delay ("interaural time difference", Wikipedia tells me), but that's less than 1 msec which is too small for Renoise to handle.
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Postby tenfour » Sun Mar 15, 2009 4:05 pm

what does it even mean to "make stereo". basically you mean to add the perception of space, correct? thus, reverb + panning will give 99% of the effect imo. unless you want a less natural effect
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Postby fbjon » Sun Mar 15, 2009 5:31 pm

tenfour wrote:what does it even mean to "make stereo". basically you mean to add the perception of space, correct? thus, reverb + panning will give 99% of the effect imo. unless you want a less natural effect


That's right, but panning and reverb won't quite cut it, I would say, unless you're aiming for a very large space. Panning doesn't make a natural stereo image, it just adjusts the levels reaching each ear. In real life, there's also an additional delay to the ear that's farther away, and that ear will also hear slightly less high frequencies. Additionally, in a room the farther ear will receive room reflections for a particular sound source differently than the other ear. All this together is something like how the brain determines where a sound is coming from, or at least distinguishes them from each other.

Reverb can do it, but not the usual ones like what's built-in to Renoise. You need convolution reverb that can simulate an actual physical space that you have recorded an impulse response from (there are some plugins for this):
http://en.wikipedia.org/wiki/Convolution_reverb

It's like the difference between a pair of mics in a room vs. one mic for each instrument, put together at the mixer table.
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