I am not engaging the ALC, but the limiter, is an option under the 'ALC' options. Under ALC there are options such as 'on', 'off', 'limit', and 'limit +12'.
A Limiter automatically limits the peak levels, so engaging the Limiter is a partial form of Automatic Level Control (ALC). I assume setting ALC to ON, rather than to Limit, will automatically control the gain as well, much like AGC on some cameras.
If my way of telling if there is more noise was illogical, then how do you judge the quality of the of the limit? I cannot tell a different by listening regularly between 'limit', and 'off'. I cannot tell which one has more noise, because I can't hear additional noise. So if turning it up in post to hear it better is illogical how do you tell?
If you cannot hear a difference it is because you are not hitting the limiter or because your monitoring system simply can't resolve the difference. However, if you hit the limiter hard enough it should be noticeable even on a fairly poor/cheap monitoring system.
Here's the tests I would run:
1a. Setup a consistent sound source, preferably one which has not already been limited (!), an analog clock would probably work OK. Set your ALC to OFF and setup your mic close to the clock, close enough that you need a low mic-pre gain setting to reach a -12dB peak. Once you've got a -12dB peak level, record 15 secs or so.
1b. Without moving the mic at all from test 1a, whack the gain up by about 16dB-18dB, so every tick is easily exceeding the clip point (0dB) and set ALC to Limit. You should not now be clipping anymore, record another 15 secs or so.
2a. Set ALC to OFF. Setup the mic quite some distance from the clock, maybe 3m or so, until you have to turn the mic-pre up to say 80% to get the ticks peaking at -12dB. Record 15 secs or so.
2b. Without moving the mic at all from test 2a, lower your mic-pre so the ticks peak at about -24dB. Set ALC to Limit +12. Make sure your ticks are now peaking at -12db, adjust your mic-pre if not. Record 15 secs or so.
Now you can compare in your NLE:
1. Compare 1a and 1b by increasing the level of 1a and decreasing the level of 1b until the level of the noise between the ticks sounds the same loudness on both. The ticks in 1b should be quieter than in 1a and they may also be distorted in some other way, caused by the limiter. By repeating this test, hitting the limiter less hard, you can determine the effects of the limiter; how clean it is, at what point it starts reducing dynamic range, etc.
2. 2a and 2b can be compared in your NLE directly, without any changes, listen out for the difference in the amount of noise. You will want to repeat test 2 (2a and 2b) by moving the mic closer and further away from the clock, so the mic pre (with ALC set to OFF) needs to be set at different gain settings to achieve -24dB ticks. For example, with the clock set far enough away that the mic-pre has to be set at 95%, you should very clearly hear that 2b has less noise/distortion than 2a. The idea behind repeating this test is to find the mic-pre gain setting at which 2b has less noise than 2a (when 2a has 12dB of gain added in post). You will know in future that when on set and you need to set your gain beyond that point, you will get cleaner results using Limit +12 rather than just Limit.
G