Limiter indicator led


I am looking for a very low instruction usage setup which can switch on a led when the treshold of a limiter is reached.

I have this setup:

But the signal detection block, stays on too long as the shortest reset time is 2 sec (why??)

I tried all other compressor/limiter blocks with flag or signal compression out indicator out, but I can't get the LED to work then at all...

First question is can I use a standard compressor/limiter block too achieve my goal and how? So replace compressor block 2 or 3 with a built in indicator option? And how to attach a Gpio pin to that (external circuit just reacts to a low/high output)

Second question: Is there any source of information that explains all the blocks in sigma studio available which explains in detail, what exact signal the available pins on a block are carying and/or what they do... I have done many searches, but found almost nothing... It is very confussing at times as similar indicated pins are labeled completely different.

Hoping on some help ;-)


  • 0
    •  Super User 
    on Jul 20, 2017 6:37 AM

         Hello Bazeman,

         The easiest way uses the Limiter's flag output directly driving a GPIO as shown below.  In this case the LED's ON duration depends on the Limiter's decay setting -- with the numbers shown below the LED blinks nicely on audio peaks.  Note that the Limiter's center pin is the flag output; it is incorrectly labeled.  Also be sure to set the GPIOs as outputs in HW Configuration (this differs some depending on which DSP you're running).

         Another way works with compressors lacking a flag output -- we can make one ourselves by comparing the compressor's input to its output, lighting the LED if this difference exceeds a set threshold.  As implemented below this works fine as long as the compressor's curve is set at unity gain when not compressing (i.e., no expansion).  If you have the compressor graph set up to also expand (increasing gain above unity at low levels), it may be necessary to use envelope followers both before and after the compressor(s), then compare these levels afterwards.

         The GPIO Outputs go high (light the LEDs) with any nonzero signal at their input pins, even one LSB -- thus you need the ABCD comparators as shown to provide a larger threshold.  Otherwise the LEDs would stay on for many seconds, waiting for the difference levels to decay to absolutely zero.  This also caused the long delays which you were experiencing with the circuit you described.

         The best source of SigmaStudio algorithm info is the Toolbox wiki:

    SigmaStudio Toolbox [Analog Devices Wiki] 

         Best regards,