The modulation of the Baofeng UV5R has a (bad) reputation of sounding (too) weak and ‘muffly’,
making my device useless, to be honest.

Louder audio, combined with an enchanced high frequency response, is ‘the’ solution.

Edit: before reading further, listen to this recording in MP3 or OGG.
This is a recording captured from the PI2NOS repeater stream where I have a QSO with PA3MRF.

PA3MRF uses an unmodified UV5R and I am talking through my modified (read further ; -)  UV5R.
Even when you don’t understand anything, the louder one . . . is me ; -)

Edit2: Quickly after this QSO Marcel PA3MRF modified his UV5R.
To hear the difference listen to a recording in MP3 or OGG.

I ‘misused’ the VOX-amplifier (Q17) to boost the audio, and removed C135 (47n) to eliminate high frequency cut offs.
The Q17-emitter resistor decreases the gain of the Q17-amplifier somewhat. Values around 500-1000Ω work fine.
Because there is ‘much’ space around the Q17-emitter, a variety of SMD resistors may be used (I used 0805).
Decreasing the value of R75 (to ~220k or so) has the same effect. However, I did not have such small SMD resistors.

Update: PE7M applied my mod successfully (with R-emitter = 430Ω) with very good results (I used 680Ω).
His (detailed / hi res) pictures may follow soon.

Visualised below are my mods to improve both the modulation index and audio response
significantly. Please refer to the procedure(s) to dismount the UV5R (available on the web).

Disclaimer: opening an UV5R and applying this modification is (at) your own risk
and/or responsibility!