Ok, let's go back in time when CB amateur radio was introduced. This was your signal chain:
- speak inside a (small) room, like inside a car // comb-filter
- transmit with quite limited bandwidth
- use high compression many times
- receive with limited bandwidth
- listen to a tiny speaker // comb-filter
Comb-filter effects arise from sound waves traveling different routes to the same spot, resulting in a difference in wavelength, resulting in amplification or anihilation. Just have a look at the drawings or listen to the audios. This is one major effect for this nasal and often hollow sound just look at the comb filters characteristics).
Bandwidth: try a low-pass with about 1.2 - 2.5 kHz, roughly; or replace it by a bandpass, to cut away some of the low frequencies, too, to emphasize the higher ones when listening.
Compression: It's basically a non-linear transfer characteristic, so you'll add a lot of distortion, hence overtones. Make sure, to suppress higher components enough by the filter.
So a simple setup looks like this:
- comb-filter (first set of parameters)
- compression (second set of parameters)
- bandpass (say ~200 Hz - 1.5 kHz, roughly) (third set of parameters)
This should give you enough complexity to vary sound and approximate what your videos show.
P.S.: Short verification, using Ardour and Calf plugins with Linux
- right upper: signal chain Fader, comb filter, compressor, lowpass
- most important: comb filter
- lowpass to single out the singer
- almost irrelevant : compressor (bypassed)
Lower left shows you some impression of a comb filter. Set the two parameters, so it sounds a bit artificial, as wanted. Varying these two parameters while playing result in a phaser- or flanger-like sound.
Tuning the lowpass (lower right) close to the transmission limit of CB-radio, while introducing some resonance. This way focus on the singer is even more increased.
So with these 6 parameters (2 from comb filter, 4 from filter) a wide range of sound manipulation is possible, which your DAW can further automate, if needed.