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#6360 - 05/23/10 01:34 PM Understanding PSP Xenon...
Mr_Mustard Offline
New Member

Registered: 05/23/10
Posts: 1
I love Xenon, it is my favorite limiter, however I feel like I do not understand it completely from a technical stand point and am not finding clarity for everything in the manual.

I do understand Xenon works as a 2 stage limiter. I think I will run through how I think Xenon works and hopefully someone can come in here and shine a light.

The Transient modes pertain simply to the second stage of limiting. Mode A works as a hard clipper, Mode B works as a look ahead limiter and Mode C also works as a look ahead limiter but with a further look ahead (its often cleaner than Mode B but softer to the transients).

Now the Transient knob pertains to the first stage of limiting which essentially functions as a brick wall limiter without any look ahead (is that correct?). The Transient knob adjusts the attack time of the first limiter, 0% being the fastest attack and 100% being the slowest. With the Transient knob at 0% (very fast attack) nothing goes to the second stage of limiting, with the transient knob at 100% (long attack) everything goes to the second stage of limiting.

So in a sense when you are using Mode A and set the Transient knob to 50% you are limiting a good portion of the medium length transients while allowing the shorted transients to go through to the second stage of limiting, in this case (mode A) the hard clipper.

Do I have a proper understanding here?

Basically I would like to know more about how the first stage of limiting works. Is it a look ahead limiter? Are the attack and release times simply there to guide a built in auto time function?

I have noticed that if the Transient knob it set to 0% changing modes A,B,C has no effect leading me to believe that 0% = all first stage limiting and 100% = all second stage.

If someone can help that would be great.

Thanks.

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#6388 - 06/09/10 03:10 AM Re: Understanding PSP Xenon... [Re: Mr_Mustard]
Hubert Pietrzykowski PSP Offline

Member

Registered: 08/21/02
Posts: 308
Loc: Warsaw
What you wrote is almost true, but not 100%.
The first stage is not brickwall - if it was it wouldn't let the transients through (when saying that 'it lets the transients through' we mean that the output signal of the limiting stage contains samples that exceed 0dBFS). So, to pass some transients the first stage is not brickwall. It does have some lookahead, but it's not essential to take it into account to understand how Xenon works. The most important thing to keep in mind is that some (fast) transients are passed. How much is passed is controlled by transient knob, which sets the first stage attack time - the faster the attack the greater probability that transient will be catched (the limiter gain reduction will get deep enough to attenuate the transient on time so it becomes <= 0dBFS).
Now the second stage is where those fast transients are processed. As you said - the first mode is hard clipper while other two are soft, lookahead, modes. All three are brickwall - capable of catching all transients.
_________________________
Hubert Pietrzykowski
DSP Engineer
PSPaudioware.com

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