Gate

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gilzad
Posts: 92
Joined: Wed Dec 19, 2012 6:46 am

Gate

Post by gilzad » Sun Dec 30, 2012 1:21 am

The other day organic_io asked me on the Renoise forums, if I could show him how one can build a Gate by inverting the compressors output and adding it to its source.

I thought there could be more users who'd like to have a Gate, so I'm posting it here.

(Right-click to save)
Example file.
Sunsynth module. <- updated to use the new compressor now
Old Sunsynth module.

Background
Spoken very simplyfied, a compressor just raises the signal after a specified time (Release).
A Gate does the opposite. It quietens the signal after a specified time. (again, Release).
Now, if we want any DSP in Sunvox to do the opposite of its job, we can simply use the cool 'invert' feature in the Aplitude module and add the output to the source signal again.

The example file
In this example, we take a Generator as a source signal. That signal will be sent into a compressor and into the Output module.
The Compressor's output will be sent into an Amplifier module whose 'Invert' parameter is set to true/1.
Now we connect the compressor to the Output, too.
In theory, any part of the Generator's signal, that has not been manipulated by the compressor, will be killed on the output. Because the original signal (e.g. +1) will be added to the inverted signal (e.g. -1). Only that part of the signal, which has been manipulated by the Compressor, will no longer be the exact opposite of the original's source. That turns the Compressor into a gate.
But only in theory, because any Compressor will add a little amount of latency to the signal, thus even the uncompressed part will not be the opposite of the source signal, but a delayed one. You'll get some cool sort of a chorus effect, but we already have a Delay module ;)
So the only thing we have to do, is to apply exactly the same amount of latency to the source signal, before we add it to its inverted version. This is simply done by putting another compressor into the chain, whose Slope parameter is set to zero.

What is happening
What happens now is the following:
A signal comes in, that would pass the Compressor's threshold.
The Compressor quietens the signal after the specified Attack-time. Then, if the Threshold isn't exceeded anymore, the Compresor will raise the signal again after the specified Release-time.
This manipulated signal will be inverted and then added to its uncompressed source.
Now during the Compressor's Attack-time, the inverted output will be the exact opposite of its source, so you won't hear anything.
After the attack time has passed, the quietened signal will be a quieter opposite of its source, thus you will hear a remaining difference of 'source+opposite'.
If a signal does not exceed the Compressor's Threshold, it will again pass the Compressor as the exact opposite of its source and thus be killed by 100%.
If a signal exceeds the Compressor's threshold, it will pass the Compressor as a lowered/quietened opposite of its source and ideally not be killied at all.

Exactly for this case the 'wrong' routine of SunVox's old compressor is so much better for a gate, because it can kill the signal by 100%, if it's loud enough. That's why the old version of the Gate is still provided here.

Thanks go to my friend, Niklas Winde, who once tought me how to create opposite effects with inverted signals using his large analog setup.

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