rtlmic: Wireless Microphone Receiver for RTL-SDR

Over on GitHub a new program called rtlmic has recently been uploaded. The program descriptions reads: 

rtlmic is a multichannel FM microphone receiver/demodulator for RTL-SDR cards. It outputs realtime audio to JACK.

Basic usage is simply:

$ rtlmic [channel 1 frequency] [channel 2 frequency]…

This program may be able to be used as a replacement for wireless microphone base stations at events. The software allows you to capture as many channels as your CPU can handle, within the active bandwidth of the RTL-SDR. There are also settings for tweaking the companding ratio and tau, deemphasis tau and FM deviation all of which affect the output audio and can be used to optimize the frequency response of the microphone.

The audio outputs directly to Jack audio which is an audio piping API, which simply routes the audio out to wherever you choose it to go.

A typical wireless microphone base station and microphones.
A typical wireless microphone base station and microphones.

4 comments

  1. snn47

    Recently I had asked the same question to experts on PMSE equipment, and was told anything above 4 to 5 ms delay is unacceptable to artists, e.g. if used for retransmission for in ear monitoring.

  2. ReadyKilowatt

    Interesting concept. Any idea how much delay is introduced? I know jack is designed to be low latency but my experience with some SDR programs is that there is significant delay. That could be devastating to someone trying to use this for musical performances, and could be very distracting to simple speech.

    • Tehrasha

      My guess is that the delay is kept minimal by having the SDR only sample a very tiny portion of the spectrum, unlike most software sampling and processing 2+Mhz worth of spectrum, and then demodulating the wanted 10khz worth of signal from that.

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