Thresold Measurements

J

Jack Hammer

New member
the threshold control has 0 to -20 to the right and 0 to +20 to the left. What does this mean? Which way rasies the threshold and which way lowers the threshold and what does raising and lowering the threshold actually mean?

I am familiar with compression and know how to use the device however I do not understand wha the negative numbers in decibel langauge means. I did down load an explanation someone sent but it was very long and involved and I did not have time to read and undersant it. I cannot find it now and simply wish someone that knows would provide a simple working definition of this phenomenon in the recroding studio.
 
I'm as mystified as you are. Usually threshold is expressed in negative increments. I don't know what a positive threshold would be. I didn't notice if you said what compressor this was.

If it's an expander too, maybe it has something to do with the expansion function? (negative for compression, positive for expansion?... just a wild guess...)
 
It's the point above which the compressor begins to kick in. Analog voltage levels extend above zero.
Take a signal that peaks up to +8, a threshold setting of +4 would only effect the top four db of the signal. Set at -4, the top eight would be compressed.
:D
 
Okay, but why then would the setting of -4 not effect the top twelve or the equivalent of +4 to get to zero and then the +8 on top of that?

I think som eof the confusion comes from defining what is "above" the threshold and what is "below" the threshold. For instance, if we say that everything below the threshold is cmpressed and set the threshold at +4, why would the top 4 be effected and not the bottom four or the amount of signal actually below the threshold.

I tend to imagine the threshold as a line going straight across the graph where the left or up and down part of the "L" shaped graph represents the threshold and the bottoom I suppose is the ratio. In this scenario, everything below the threshold is, to me, everything below the threshold line.

the question then is what is compressed, the information below the threshold or above it?


Having made that determination, I still would like to know why there are negative numbers. Why not have the scale start at zero represnting zero decibles and go up from there. This way, if you wanted to compress everyting below 5 you would set the threshold at 5 and 0 to 5 would be compressed.
 
Having said all that ai realized that the rest of the confusion is becuase the threshold is the point where the compression starts so that compression is everything above the threshold. the negative numbers almost make sense to me now.
 
You need to understand how the decibel scale works.

Negative means less than some reference level. Positive means more than some reference level. What is the reference level? Probably one of the two nominal "line" voltages: .316 volts or 1.228 volts.
 
Now that makes sense. If the reference is not necessarily zero, then plus or minus have different meanings. So how does one go about determining this for a particular piece of equipment.

But just to be certain, now you are saying that a setting of, for instance, -10 would be 10 decibles less than the nominal input or level. (measured in the standard that applies which is another story as I undersstand the issue- dbv or dbu or something like that).

By the way, I do aplogize for my struggling to fully understand this concept. It is not that I cannot operate a compressor and get very good musical results, it is just that I wish to understand a bit better what I am doing when I do operate the machine so that ultimatley I can get even better results. In this regard, I truly am thankful for those that have been patient and helpful and have generously shared their time, knowledge and experience.
 
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