Noise on music player & cellphone

[Menticol]

Hello guys!

Some days ago I have tested a homebrew amplifier using my generic music player (and then) my cellphone as test signal sources. During the tests I noticed a strange noise coming from the speakers, consisting on high pitched clicking-buzzing-whinning sounds. Please note that the noises are not the typical rattling sound that is heard when a cellphone is placed near an audio device and a call is incoming or outgoing. The noises are more like a 96 kbps phone modem or a badly tuned AM radio.

At the end, I assumed the noises were result of poor amplifier construction or bad shielding and decided to continue the project later.

The thing is, tonight I'm playing some music on the cellphone (using headphones) and noticed that the sound actually comes from the phone itself!!

Naturally the noise ruins the listening experience and it persist even when volume is set to 0. But I find interesting the fact that the noises are actually synchronized with the task that the cellphone is doing (i.e. reading the beginning of the file: buzzing, skipping between tracks corresponds to whinning, navigating on the menu causes rattling, etc).

But the major surprise was yet to come, came after I tested the mp3 player and found exactly the same noise!

I already assume that my devices are irreversibly damaged, but I wonder: What actually causes the noise? Why this noise is identical to the sound of AM radios operating near badly shielded PSUs or computer equipment? what went wrong inside the cellphone and the music player?

Thank you by your inputs

PS: The files are 320 kbps audio, and both the cellphone and music player operated normally before the amplifier test.

 

[dr pepper]

Sounds like digital noise getting into the power supply or through rf on to the audio stages, not necessarily from the rf stages within the 'phone, could be from the processor side.
Is it a cheap phone?

 

[MikeMl]

Any chance that the "noise" is recorded into the mp3 files, so that you hear it regardless of which player you play the mp3 on?

Any chance that the "noise" is actually copyright protection?

 

[cowboybob]

Download a free app called "WavePad Sound Editor" (there are several options for this).

If you feed the output of your playback device into the PC's mike input, with the above software in place, there is a Record function that will allow you to record and observe the waveforms being reproduced.

From that you might be able to determine the source of the "noise"s you're hearing or, at the very least, post "snips" of the offending waveforms for the audio experts on ETO to ponder.

I can offer assistance using WavePad.

 

[dr pepper]

Mike, do they use noise as copywright protection?
Obviously not random noise if so.