Audio filters in MP3 outputs

RTLSDR-Airband uses LAME library to encode PCM streams into MP3. LAME can optionally apply lowpass and/or highpass filtering to the encoded audio stream. Cutoff frequencies can be specified per channel, using lowpass and highpass parameters:

channels: (
  {
    freq = 123.00;
    lowpass = 3200;
    highpass = 200;
    outputs: ( ... );
  },
  ...
);

By default, filters are enabled and their cuttof frequencies set to 2500 and 100 Hz. To disable any of the two filters, set its cutoff frequency to 0.