TOPIC:

Hi,
I want to apply compression to my Flex Digital output above a specific level.
Input signal to Flex Digital is digital and volume control is downstreeam from a separate DAC.
Do I have this right: when I set the channel output (or input) to say +12dB, and apply compression from upwards of 0dB (threshold), how does that work?
Does the compression threshold refer to the actual output signal (as modified by output or input gain settings), or to the original input signal?
The manual says 'full scale' but doesn't specify of what.
So if I set the output gain to +12dB, and the compressor threshold to -12dB, the output will be compressed as soon as it gets above the level of the original signal?
I guess the basic question is where in the chain is the compression applied (and threshold referring to), relative to the input and output gain settings.

Jan Didden

The +12 db is actually 0dbfs 

they made all the outs at unity at -12db

that leaves 12db of headroom , don’t run the outs up that much if you don’t neeed to 


compressor cuts power as you get louder, to save speakers from transients that could be expected while modest volume you want everything to match 
Set the attack and thresholds properly to the top end of the signal…. -25db with a ratio of 4:1 is pretty common iMO to save your shit from accidents or abuse 

it works nice to dummy proof your system from someone that accidentally turns it up to max or a kid who gets to your system 

Ahh that's good to know, thanks for the numbers.
Doesn't answer my Q though: what does the compressor threshold refer to?
Output level, input level?

Jan

Jan,

It would make sense the compression threshold was independent of volume control setting and only based on the output level sent to the DAC's, yes?
I've never used the compression feature of the miniDSP units, but you've raised a good question.
I know you have the chops to bench test and evaluate this effectively.

I will put this on my to-do list as well.

Dave.

That's a good logic, yes.
I'm certainly equipped to measure it but will not be able to do it for a few more weeks.
I was hoping someone knew or dev_team would chime in
I'll post here when I get to measuring it.

Jan

I see what you alls mean now… humm that is a good question 

thanks Dave for helping. I would also be curious as well 


andrew 

The comp/lim on our platforms works the same way as all comp/lim. The Threshold value is indeed the "input" signal to the Comp/Lim processing block. 
i.e. the RMS value before the compressor kicks in.. e.g. -20dBFS = anything from infinity till -20dBFS is untouched, >-20dBFS and the comp/lim will apply based on your ratio/attack..etc.. 
Does this make sense? 

in other words, it's all "signal related" rather than gain/volume related inside the DSP. Full scale = 0dBFS (of the signal). The +12dB are gain, that's not the real signal. Does this makes sense? 

Here is a summary of the typical features of the comp/lim. 
producerhive.com/ask-the-hive/compressio...hats-the-difference/

Yes, I understand that the limiter acts on the limiter input - how could it be different?
But what is the limiter input? Is it the input signal coming in from the input?
Or is it the output signal as it would be if the limiter would be disabled?
If the former, then the limiter output could still be gained up after the limiter.
I think that makes a difference, or does it not? Maybe I have a blind spot here.

Jan