Yes, rockbox´s AGC-safety-clip rules!
I always start at +20dB internal gain(set as max. gain to avoid noise of the internal preamp) at the venue´s toilet where i get the iriver out of my pants HAHA!
I record in WAVPACK(lossless format =>WAV 16 bit) and it takes 4h55min until 2GB are reached and a new file begins.
I use the sennheiser mm-hlsc-2 or the sp-cmc-8 cardioid mics with a 9v batterybox.
Usually the level goes down to +9db or +18dB depending on the venue and the sound pressure level.
As petur said before, it´s only decreasing but NEVER boosting levels and thats exactly what we all do when setting levels manually.
You shouldn´t go over +20dB internal gain to avoid the internal preamps digitals noise which occures considerably at a gain above +20dB.
For the case of recording silent sounds use an external preamp of microphone madness, chris church or soundprofessionals which have less noise than the internal preamp.
Never again manual checking of levels

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good luck
Arni