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I am piping audio from my MacBook into my Raspberry Pi 3B.

MacBook -> Headphone output of USB soundcard -> TRRS cable -> RasberryPi jack input

I am then running it through a DSP algorithm which should decode the signal perfectly.

However, on my setup it is failing to decode the signal.

A couple of my teammates have it working (but sporadically). [EDIT: Turns out their setup is different, see answer].

Is there anything I need to take into account here?

Do I need to insert some resistor/capacitor circuitry?

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    The Raspberry Pi has NO "jack input" - it is OUTPUT only. – Milliways Sep 26 '19 at 22:57
  • it is frequently failing to decode the signal - by frequently you mean always – Jaromanda X Sep 27 '19 at 2:58
  • @Milliways Two engineers on the team are experiencing intermittent success, so it must be possible to configure it as input. – P i Sep 27 '19 at 7:12
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    The circuit is published. The Pi has ABSOLUTELY no analog input so it is impossible. – Milliways Sep 27 '19 at 7:28
  • Thanks @Milliways That was the problem. My route was wrong. – P i Sep 27 '19 at 8:16
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(Thanks @Milliways) I was using an incorrect route.

The RaspberryPi has no audio input. It is not possible to configure the jack for input. It is OUTPUT only.

The correct route is: 

MacBook AudioJack -> TRRS cable -> MicIn-of-USB-Soundcard -> Rπ USB

Now my Rπ is able to decode the signal.

The problem of intermittency experienced by one developer is likely in the Laptop Jack Spkr <--> USB SoundCard Mic step, and therefore not a Rπ issue.

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