Using RTLSDR in direct sampling mode with OpenWebRX

First, you will have to setup keenerd's fork of RTL-SDR, as it has the -D switch for the rtl_sdr tool.

git clone https://github.com/keenerd/rtl-sdr
cd rtl-sdr/ && mkdir build && cd build
cmake ../ -DINSTALL_UDEV_RULES=ON
make && sudo make install && sudo ldconfig

Then, you have to add the -D switch to config_webrx.py.

start_rtl_command="rtl_sdr -D1 -s {samp_rate} -f {center_freq} -p {ppm} ...
                            /\___ this is the switch to add

-D1 means that the dongle is set to direct-sampling from input 1 / I.
-D2 means that the dongle is set to direct-sampling from input 2 / Q.
-D3 means that the dongle is set to no-mod direct-sampling.