Hfrhyu

What is the maximum voltage for common music files?

When playing back on a smartphone, if the volume of the smartphone is set to maximum, how much voltage is sent to the earphones of the electric signal?

thanks so much for comment
I’m japanese.
I’m not good at English.
I use google translator.
I want to use a low frequency therapy device on my smartphone. I thought it was dangerous depending on the voltage. And I asked this question. any precautions or dangers?

Amplification

It does not depend on the music file, but at the amplifier sending the music to a speaker, or to a headphone/earplug connector.

Music file

A music file only contains 'values', and mostly in a compressed form. After uncompressing, you get values which has a certain amount on bits per value (typically 16 or more).

Conversion

A microcontroller can send these values to a speaker via an pre- and/or amplifier, which converts it into actual voltages. So it depends on the amount of amplification.

Protection

Also note that sending continuous 'max values' do not result in a loud sound, actually it would breaks the speaker (to prevent this, in the amplifier a so-called DC speaker protection is present). A wave is needed to let the speaker move outwards and inwards very fast, and this is done by sending changing values to the speaker.

Measure

If you want to measure, you can use an oscilloscope to measure the audio output while sending a sine wave with a maximum amplitude.

These days a lot of DAC chips for consumer equipment use voltage output of 2 Vrms.

The supply voltage is largely irrelevant, as a lot of DAC chips also use internal charge pumps to boost up supply voltage and to generate negative supply voltage for the audio output stage, so they can drive DC coupled loads directly.

Normally it's limited by the cellphone battery voltage, which is about 3.7V. However there are other limits in play like the EU volume limit of 100dB - which is specified as SPL rather than a voltage.

A line input level electrical signal typically has a voltage ranging from 0,3 to 2 Volts. "Line level" is the term for the standard used between a whole bunch of devices, namely your cell phone.

Be sure to read the other answers as they will make you aware of the specifics of your question.

The music files like mp3 have only digital logic levels (0's and 1's),
First the analog signals get converted into digital logic using ADC's. The ADC works like a charm here, they slice the analog signal into some simple form, the slicing frequency (sampling frequency) depends on ADC.
Now, these sliced pieces get converted into bit's (each bit represents some voltage) so the processors/controllers can understand slices and store them, usually these slices has huge data (0's and 1's) so we compress this data using mp3 compression or some other audio formats.
When you play a music file the 0's and 1's go to DAC which convert them back to an analog form, the voltage here depends upon your DAC's reference (this limits the swing of analog signal)
Here the signal is weak so we amplify it by an amplifier and feed it to speaker.
Earphones speakers are driven between 0 microvolts to 10 or 15 microvolts.