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For file format, ensure that you're using WAV files, mono (1) channel, 16 bit depth and 44.1kHz sample rate.

There's no need to adjust audio levels, because resamplers will normalize the volume of all notes to be the same. If you lower the P flag, the volume levels will be closer to how they were originally recorded. If you plan on using lower P flags, make sure to record your samples at a consistent level. (eg. same mic level, same distance from mic, etc.)