Sorry if my question was not clear enough.
I think, that the equation for calculating the AT, TAV and RT coefficients is wrong. And after bit of fiddling in Octave, I can prove it is indeed wrong.
We are talking about this eqn from the Zölzer, page 98:

this eqn should give us the constant to this kind of one-pole low pass filter structure, as seen from the figures 5.6, 5.7 and others (a section of Fig 5.7):

The time constant, is the time constant of the filter, i.e as in the BBC paper: omega = 1/tau. Tau is either the AT or RT time constant (attack/release time constant) of the filter element.
By plugging some numbers in Octave, I have concluded, that the equation K = 1 - Exp(-2.2 * T/t) is flawed. The measured time for the exponential to reach 63% was very incorrect.
I am certain, that this equation for a one-pole filter is correct: K = 1 - Exp(-2*Pi * fc/fs)
By substituing both fs (sampling frequency) with Ts (sampling period) and fc (cutoff frequency) with the time constant (which relates to fc = 1/(2*Pi*tau), we then get:
K = 1 - Exp(-T/t)
Verifying in Octave shows a correct result. I have put into Octave the whole structure from Fig 5.7 (Zölzer pg 98). The Octave .m file is attached, if you want to look.
I have absolutely no idea, where or how the 2.2 constant got there. It ain't right. Plot below with the corrected formula above, yields correct time constants for the filters. Plotted for 4ms attack and 50ms decay.

Also, I noted that the RMS detector in Fig 5.6 has an error in it, apart from the missing square root on the output: There should very likely be a minus sign at that summing node.

.m file in zip archive:
AT_RT_filter.zip (0.75 kB - downloaded 43 times.)
//EDIT: FUCKING HELL, the forum randomly swaps the attachments. SHIT!!!
//EDIT2: COrrected.
//EDIT3: Added time constant description for the plot.