someone can help me?
i try to read frequencies of music with trrs 4 pin
i try to serch something but no results.

share the code and photo or fritzing scheme.

with trrs 4 pin

What is this? Please post a link to it.

What are you going to do with the frequency detection?

You can find examples (and YouTube videos) of [u]FFT[/u] or FHT to make spectrum analyzer effects. (These are effects, not precise-spectrum scientific instruments).

Or, people have used [u]autocorrelation[/u] to make a guitar tuners but as far as I can tell, these tuner-projects are not often successful.

[u]This page[/u] shows the TRRS connections. If you only want the audio-out (and you don't need the headphone connection) you can use a regular TRS headphone plug. ...That's the easy part.

The Arduino can't read the negative half of the audio waveform so you need to [u]bias the input[/u].

The Arduino can read 0 to +5V DC , or 5V peak-to-peak AC (1.75V RMS) when biased at 2.5V. That's about right for a line-level or headphone-level signal. If you're using a microphone you'll need a preamp.