Hello there!
I am a bit new to Sigma Studio
I found the Compressors in Dynamic Processors section of the Sigma Studio GUI
What I would like to understand is the following
1. Unlike traditional Compressors a few of them like the one below do not have any Attack/Release time settings . How then do i set the attack and release times in such modules since these are important parameters as you would understand.
2. I do see Hold / Release times … Are these fair substitutes of Attack/Release times ? What is the RMS TC ? why is its units expressed in dB/s
3. If I would at all need to setup attack/release times for my Compression then how do I set them up using these same modules
(I have seen few modules with explicit options to setup Attack/release times) but how are they different from ones that do not have attack/release time setting options.
Regards
Hermione
Hello Hermione,
This page in the SigmaStudio wiki describes how the RMS Compressor's RMS-TC, Hold, and Decay controls work. You'll find that the RMS-TC determines the Compressor's Attack rate, while the Decay figure controls the Release rate. Both of these are rates, inverse to time -- higher numbers mean faster or shorter time. Perhaps the best way to see how the compressor works is to build a test circuit and play a little bit. In other words, we can have a SigmaDSP project test itself -- No external equipment nor soldering iron needed!
Here the RMS Compressor's table is set as a 0 dB limiter -- it wants to impose a limit of 0 dB = 1.0 pk. The oscillators build a modulated test signal alternating from 0.5 pk (below threshold) to 2.5 pk (above threshold), which forces the compressor to react. As seen on the Real-Time Display, the Compressor's attack appears exponential -- it has a long "tail" like the curve of a capacitor discharging. Typing RMS TC into the EZ Search box pulls up dozens of posts, indicating that this has been a hot topic over the past nine years. In these results you'll find a formula for converting RMS-TC to time constant. Some time ago I made some measurements to produce this table. It's for a Limiter, but the Compressor works the same:
The test circuit shows that the Decay characteristic is linear, not exponential (even though it's also labeled as dB/S, which describes an exponential characteristic). You can adjust this to taste via a listening test.
Finally, the Hold setting introduces a feature often missing in analog compressors -- it waits a moment after an Attack before starting a Decay. Any Compressor's signal measurement includes ripple, which if allowed to modulate the gain produces some distortion. If you set the Hold value to 1/2f, where f is lowest audio frequency, you eliminate the ripple and thus the distortion. I've measured no increase in distortion with a Compressor in use.
Best regards,
Bob
