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FM Transmitter Noise (not what you think)

Started by marksat, September 28, 2021, 06:26:55 PM

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marksat

OK, this one is a tough one:

I am running FPP in a Debian 11 virtual machine (using VMWare Player on Windows 10).  So far everything works well with the exception of the USB FM Transmitter.

The Transmitter works, but there is random noise (not constant).

To be clear, I used this transmitter last year on the same PC with XSchedule (yes a cheap one from A-zon(https://www.amazon.com/Mini-Digital-FM-Transmitter-Module/dp/B01N7DIRE9/ref=sr_1_3?dchild=1&keywords=Icstation+Digital+Audio+Transmitter+Stereo&qid=1632874484&sr=8-3).

I also tested this just using the Windows Groovy player playing the same .mp3 over FM and it sounds fine (again on the same PC).  This tells me that the radio signal is good (eliminating other interference, etc.).

When I play the sequence/mp3 using FPP (again in a virtual machine), then there is the random noise.

FPP recognized the USB device right away and I did not have to change anything except selecting that for the output.

I am going to try Virtualbox to see if that issue still persists (and maybe even on another PC).

Anyone have any other suggestions (aside from trying some other device or sound card+transmitter combo) - maybe there is a way to change the device driver or does the .mp3 somehow get changed when you upload it to FPP, etc.?

Thank you in advance.

JonD

When the audio source and speakers use the same power source you can get a humming sound sometimes.  A buzzing static type noise.  I have used a "Audio Ground Loop Noise Isolator" in the past and they have resolved the issue for me.  I don't have have a FPP and can't tell you that it will resolve your issue, but might be something to look at.

https://www.amazon.com/MA-Audio-Ground-Isolator-Stereo/dp/B09B9TS6ZW/ref=sr_1_2_sspa?dchild=1&keywords=sound+isolator&qid=1632880017&sr=8-2-spons&psc=1&smid=A2J9ERDSC0OAXF&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExUlY0UkwxSUZRMjQwJmVuY3J5cHRlZElkPUEwODg4OTMyS1k0UkhWVzVFWU9RJmVuY3J5cHRlZEFkSWQ9QTA5NDg1OTUyTDVZSlFFWTFQTVJQJndpZGdldE5hbWU9c3BfYXRmJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ==

Stormyblade

I'm going to ask the obvious: are you sure you've turned the volume within FPP down to 70 or lower?

And, other than the device JonD suggested, you can also get an RF choke - a small round device that has ferrite in in that you snap onto the voltage wire of your power before it enters your transmitter. If you look at some charging devices, sometimes you'll see these little 'bullets' snapped onto the wires. Here's a link to a set of different sizes on Amazon: https://www.amazon.com/Cedmon-Pieces-Ferrite-Suppressor-Diameter/dp/B07CWCSNW9/ref=sr_1_1?crid=31AKR6UAXXAN0&dchild=1&keywords=rf+choke+ferrite&qid=1632911276&sprefix=rf+choke%2Caps%2C215&sr=8-1

marksat

I have tried various volume settings within FPP and the transmitter. I have to dismiss RF interference since the transmitter works fine with XSchedule (and the native Windows media player) on the same PC.

I will continue to experiment with other things (clean Debian-only playback, Virtualbox, etc)

marksat

 I tried this with a clean Debian 11 virtual machine install (no FPP) and also on a VirtualBox virtual Debian machine (with FPP) Both had FM Transmitter audio noise on a Windows 10 laptop host. I ended up successfully running the show with the FM Transmitter/sound using VMWare Fusion on a Macbook.   Not sure what the exact problem is with Windows 10 virtual machines, but at this point I am satisfied with using the old Macbook to run the show.

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