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Theodric Young theodric at mit.eduHi, I'm new to SDR and I have a question about the data values that are generated by the rtl_fm program. I got rtl_fm running on my system (cygwin running on Windows 7). It is sending a stream of 16-bit signed integer values to stdout which I can redirect to a file or pipe to an audio playback system, such as sox. So when I do this: rtl_fm -f 88.1M -M wbfm -s 240k -r120k -g 30 | play -t raw -r 120k -b 16 -c 1 -e s -V1 - I hear sweet, sweet music! Hurray! But how do these 16-bit integers relate to the modulation level of the carrier? I'm assuming that the values are directly proportional to the instantaneous frequency deviation of the transmitted signal. Is that right? If so, how do I determine that ratio? I'm hoping to use this to build a device that shows total modulation (as a percentage of the maximum modulation of +/- 75kHz) for an FM radio station. Also, I'm assuming that the sample-rate of the output data stream needs to be at least 120kHz because the baseband signal includes the stereo pilot (19kHz), the stereo subcarrier (38kHz) and an RBDS subcarrier (57 kHz). Any insight would be appreciated. Thanks in advance, Theodric Young