ruairioflaherty
Well-known member
Monte McGuire said:The tradition with feedback limiters is to provide an input gain control and an output level control. The threshold is fixed inside of the device, but by using these two controls, you can place the gain reduction wherever you want relative to your signal levels. Many classic ones use switched attenuators, so you can set and reset easily, or match two channels.
You could fold all of that up into one switch, but it becomes very complex and counter-intuitive for those who have used classic feedback limiters.
If you want to change the actual threshold level of the limiter, you can change the DC value sent to the rectifiers that sample the output plate voltage. However, all you're doing is changing the gain structure inside of the limiter, which will usually just make the limiter noisier. Most vari-mu stages are prone to hum from imbalance and power supply ripple, since one can't put feedback across them and still get variable gain. So, using anything lower than the 'standard' threshold voltage will probably just add hum.
I say there's no problem to fix - you just need to get used to non-VCA type processors.The whole idea of 'threshold' is from feedforward processors that have a dB-linear VCA and a real level detector, something that didn't exist until the 70s.
Good points all but as I outlined above there are some good reasons to want to have some control over a notional "Threshold" point. I make use of that advantage daily.
There may be some noise penalty to having a threshold control in a Vari-Mu (Vari-GM) design but I'm sure like every other engineering problem ever it's a compromise. Both the MDE that I use and the EAR 660 (2nd best I've heard) have a variable threshold and neither have issues with noise.
I'm a huge fan of the minimalist design of yore but I don't make records in 1960! It's a very different musical landscape now and some extra control of color is very very useful, if not essential in my work.