Sounds under the noise floor limit are considered background and are not amplified.
Threshold noise floor compressor.
This is mainly useful when compressing speech to prevent the gain increasing during pauses and so over amplifying the background noise.
When it comes to noise floor keep always this in mind the lower your noise floor the better.
If your threshold is set to 20db your compressor will progressively respond to incoming signal within the range of 30db to 10db reaching 10db below the threshold and 10db above the threshold.
Set the threshold to this db.
A 6 1 ratio is recommended.
Although post construction sound treatment is possible it is also expensive.
Something around 50db is sufficient but may vary depending on how loud the recording environment was.
In short noise floor is generally the background noise you detect in a recording file.
In compressor installations noise comes from the compressors the compressor accessories and extraneous equipment.
The compressor adjusts the gain on audio below this background level so as to prevent it being unduly amplified in processing.
The noise floor feature behaves as an expander below the noise floor s threshold.
It is amplified by the reflective surfaces in the facility.
Some best practices if followed during design and installation.
The range of the expansion is equal to the amount of make up gain employed.
Relative amount of compression compared to the threshold.
Unfortunately sound levels are often neglected during the procurement process.
That noise is usually best detected when there is no other audio signal going along with it.
Draw a graph in your head.
The ratio of the expansion is equal to the compression ratio employed.