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I've been trying to boost the maximum volume obtainable through the audio jack of my phone (Nexus 5). Instead of installing equaliser or volume boosting apps, I thought I'd go about this the technical way:

XDA forums suggest a "MOD" that involves modifying your mixer_paths.xml file located at /system/etc/ (root access naturally required) to increase your speaker or headphone volume beyond the set limits:

Find: <path name="speaker"> 
You will see this string just below it: "RX7 Digital Volume" value="88"
The value is the only part we are going to adjust.
For the mod above, I changed the value to "93". 
The default value is "88" and I would suggest not to go over "95".

To change the Headphone volume:
Find: <path name="headphones"> Look for these strings below it:
"HPHL Volume" value="15"
"HPHR Volume" value="15"
Again all we are changing is the values (ensure both are set at the same number).
For the mod above, I changed the values to "20". The default values are "15" and I would suggest not to go over "20".

How does this work? Does Android artificially limit the maximum volume and this "MOD" bypasses those limits? Or does it compromise audio quality?

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I visited this some time ago and explored some values within the file. As it can be hard to determine sound quality comparisons, I also compared the visual appearances of waveforms.

Here's a screenshot of the page:

mixer paths findings on Nexus 7 Link

Note that I only listen to audio from my Nexus7 though headphones or external speakers.

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    Consider this scenario: this answer is written by user X and you're an observer. You find that the goo.gl link is not working or is dead. Tell me, how useful would you find this answer by user X then? My suggestion to user X would be to incorporate all the relevant stuff from that link into this answer. – Firelord Oct 11 '15 at 12:15
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    Are you sure that the clipping happened on the phone's side and not in the recording process because input was simply too big for the first amplifier? Some info about your recording setup would be very interesting to know. – Sarge Borsch Nov 21 '17 at 19:56
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Actually, it's both. To preserve the user's ears and the phone's speakers, Android limits the sound output. However, changing this factor also influence the sound quality, having to high or too low distorts the sound ;)

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