GSSL Comp High Shelf question
« on: January 08, 2019, 08:13:09 PM »
Hi everyone!
I just finished my GSSL Compressor, it works fine.
I measured the frequency response of analog device in comparison with ssl emulation plugins.
I found that the analog has a +3.5 db high shelf.

You see it in the picture below. Red is an analog and purple is a plugin.

This is normal?
A higher frequencies boost audible to the ear a little and everything else is ok.
How to correct this non-linearity?
Maybe i can change some resistor values in input/output buffers?

Thanks for the help.


Re: GSSL Comp High Shelf question
« Reply #1 on: January 09, 2019, 12:24:49 AM »
Congrats on your build, and welcome to the board!

Interesting that you're encountering a HF boost with your GSSL. It's tricky when comparing to plugins as there are a number of factors to control / discount first in order to be sure what we're looking at here - the ones that spring to mind are conversion,  compression, and the comparison (I should note at this point that I don't actually have a GSSL as such, so this is all general stuff to help figure out what's going on).

On conversion, my converters for example introduce a mild high-shelf of a dB or so at the high end. Have you checked the frequency response of your DA/AD path? I can recommend the free software REW ( as it gives great, and very detailed results for this sort of thing. Comparing the response of your conversion path to that of your GSSL (in bypass, and also not in bypass but with the threshold too high for compression to occur) would be a useful exercise here.

The reason I suggest sweeping the GSSL when it's not compressing is that compression is non-linear with respect to frequency (in that different compressors react differently to different frequencies), so you may expect some changes to the frequency response when compressing with (almost) any processor. This is particularly the case with complex audio such as programme material, and more so when compressing hard.

That then leads us on to the comparison. You're encountering a difference in HF response between your GSSL and the plugin compressor - doing sweeps of the GSSL will confirm if it is actually boosting HF, rather than the plugin cutting HF.

If sweeps through software like REW do confirm that your GSSL is introducing the HF boost, we'd then need some more details of your build - for example, have you included any mods (super sidechain, Oxford, Cavendish, etc) or is it absolutely stock?

Hope that helps narrow things down.



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