abbey road d enfer said:
You have to remember that the actual timing behaviour depends on the VCA control law. The typical gain cells associated with "traditional" TC have a 1/x (hyperbolic) control law, and are used in a feedback arrangement. That makes a lot of variables.
They actually work also with "traditional" rectifiers. ATM out of my memory, but I remember having seen several examples in the past.
Your right on both points. I'm pretty sure what I don't like is the feed forward
feel. I'm probably attributing the RMS detector to that subjective experience.
One thing I don't get, is if the THAT RMS detector is already putting out a decibel linear "DC" voltage, why in all they're app notes do they tag on a full wave rectifier? Couldn't they just add a buffer for the VCA and call it a day?
JohnRoberts said:
If you are willing to melt solder I will feed you some more ideas.
Of course!
JohnRoberts said:
My concept is to use the THAT rectifier and RMS section stock, but use a small maybe 0.1uF film cap for the timing cap there, that will give too fast attack and too fast release. Then take their buffered output through my 1 pole SVF to generate different slower up, even slower down, and really slow neither time constants.
Can we do that in a feedback configuration?
And let me start my intentions once more. A limiter for full program material, coming after a compressor, that is as transparent as possible (within reason) but at the same time will not distort non transient material like voice or bass (reason for not using a clipper). I accept that the more signal gets pushed into it the more it grabs and the release sound becomes more apparent. This tends to make things sound constrained and compressed. The look ahead software limiters can go pretty deep without getting grabby and constrained sounding. I asked a plug in programmer about the L2 Ultramaximizer plug in and he said this:
The trick behind L2 is lookahead buffer. I.e., negative time delay. The
processing and detecting circuits are spread approx 1.5ms apart. The
limiter does not have an instant attack, but it kicks in before the
signal itself and manages to duck it smoothly. It would be impossible to
implement anything similar in analog domain.
In addition to that L2 contains a compressor with a fixed attack and
decay, and so if the signal is released instantly, only the limiter
circuit is triggered, while if the signal stays at a certain level for a
while, it's caught by a compressor, which would then apply a certain
release time
I don't expect to achieve what time delay can, only want to come somewhat close. The leach design is the fastest tightest sounding sidechain so far, WAY better for this application than any of the THAT design note compressor or limiters I've tried.
I am also not trying to make a full featured limiter, Its a full featured compressor, with a limiter for icing on the cake.
So circuitry wise it needs to be slim.
JohnRoberts said:
Only two op amps a small handful of discrete parts so not very complex. If you wanted to we could even make the attack and release times adjustable separately with pots.
And that sounds like it would fit the bill. Although attack and release will not be controllable to the user, just a simple threshold knob. So only for preliminary tweaking would they be necessary.
I have to say I have gotten very close with your help already...
And since beggars can't be choosers, I will try anything you draw up without great expectation or pesky demands, and will be thankful for your help and knowledge.
Ian