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We've heard this sound before (think Star Wars), and I've never tried to create it but have wondered about how it is done. Then I heard it again today here and stumbled upon one person's explanation:


"That's not ring modulation. It's Single SideBand Suppressed Carrier Amplitude Modulation, or SSB. Essentially, take an AM signal, cut it in half and remove the carrier. This means it takes up about half the spectrum and is still perfectly understandable, if not exactly broadcast quality. When receiving the signal, the radio reinserts the carrier and demodulates, resulting in that hollow sounding voice coming from the speakers." [seanc0x0 from BoingBoing]


Has anyone out there successfully created this sound before? Would love to hear your examples.

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I wish I knew exactly how sidebands and carriers worked. –  Chris Mar 22 '11 at 0:03
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5 Answers 5

up vote 8 down vote accepted

If you have access to Kyma X. There's a prototype called SingleSideBandRM in "Modulation".

It does nonharmonic frequency scaling of the input. Takes the input and does a 90 degree phase shift between the left and right channels at the frequency specified in the Frequency parameter field. Multiplies this by a QuadratureOscillator with sine in the left and cosine in the right. The resulting ring modulation gives you sum and difference frequencies but, because they are 90 degrees out of phase, the difference frequency is mostly cancelled out, leaving you with single side band modulation.

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@Jean-Edouard, that's an excellent answer. I don't have access to Kyma but it's good to know the processes behind the operation. Thanks! –  Jay Jennings Mar 22 '11 at 22:56
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Absynth has such an effect as a preset, they call it frequency shift. In Puredata there's a (perhaps more accurate) hilbert~ object. In the Wikipedia entry http://en.wikipedia.org/wiki/Hilbert_transform you need to scroll down to find "SSB modulation".

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@Jurgen, cool - thanks for the tip! –  Jay Jennings Mar 22 '11 at 16:49
    
@Jurgen, got to use this tip recently. Using Absynth I tuned the modulation to taste with the three oscillators, but I think it turned out quite well. Thanks! –  Steve Urban Feb 3 '12 at 5:06
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+1 for Jurgen's mentioning of the Hilbert~ object in PD. That object is also in Max/msp.

I think PD or Max are pretty good environments for exploring this type of thing. Most of the objects have pretty good examples as help files. For example in Max you get given this for Hilbert~

alt text

You can then use this with any audio file you like, tinker with the modulating frequency and turn the sidebands on or off. You can then record the output.

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I've never actually tried to create that effect. Interesting note though, AM signals and vocoders operate on pretty much the same principles. So, that might be one way to do it.

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To make a SSB signal look at this chip. http://web.mit.edu/6.301/www/LM1496.pdf Have a good read... Mark ZL2WHO.

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