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[MOD][Stereo][BiQuad][Audio] Stereo mod and enhanced bass using Qualcomms Biquads

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    *** Disclamer
    I made this mod for myself and I'm willing to share it with you. Install this at your own risk.

    This mod activates the earpeace speaker for playback of multimedia audio, to create a stereo sound.

    Using Qualcomms biquads, which is a hardware filter (doesn't interfere with software equalizers) in the audio codec that isn't used by default, I have been able to increase the volume and bass of the audio without harming the speakers. For this, I designed the biquads like this:

    Let's be clear about it: the earpiece speaker isn't physically designed to produce loud and rich music and doing so may be harmfull for it.
    I filtered out the low-frequency tones for the earpiece speaker because these are the most harmfull for it. Doing so, I was also able to turn up the volume a tad without sacrificing on the quality of the audio.
    This is the frequency response of the earpiece speaker:

    Main speaker
    Here I made 2 versions: 'balanced' and 'volume boosted'.
    On this one I lowered the volume of the main speaker to match the volume of the earpiece speaker. But because the low-frequency tones are quite weak on the oneplus one, I decided to keep the basses on stock level. This way, the sound is nice balanced while basses are a bit boosted. This leads to a very nice audio experience while watching video's, however the max volume is quite low.
    The frequency response of the main speaker for this case is like this:

    Volume boosted
    This is actually the same as the balanced, but the total volume is about the same as stock.
    I lowered the main speaker volume until the point where the earpiece and main speaker together produce about the same volume as stock. The low-frequency tones of the main speaker are kept at max volume. This leads to music with about the same volume, but better bass than stock. The nice stereo effect of the music is still present, but not balanced anymore.
    This is the frequency response of the main speaker:

    • Based on the latest mixer_paths.xml from sultanXDA's LineageOS 14.1
    • Stereo audio
    • Biquad filters
      - earpiece is louder by filtering out the basses (main speaker also louder)
      - A lot more bass out of main speaker
    • Perfect balance between left and right channel
    • Added some missing ULL cases and output paths


    Installation instructions
    1) Download the balanced or the volume boosted stereo mod above
    2) Flash the zip-file through a custom recovery
    (The mod will check if my 'balanced' or 'volume boosted' mod has already been installed. In case it hasn't, it'll make a back-up of the original mixer_paths.xml)
    3) Ready!

    Uninstallation instructions
    Just install the Uninstall.zip, you're back to stock.
    (I also noticed that not every ROM uses the same mixer_paths.xml, so if you lost your sound after flashing this mod, don't wory, just flash the Uninstall.zip)

    I use (and thus developed) this mod together with a dolby atmos port to get a great audio experience while watching movies and listening music. Therefore it is also optimal in combination with dolby atmos.

    This mod was a lot of work, give a "thanks" or consider a small donation if you like it please.

    Thanks To
    @abhi08638 for teaching me about the stereo part of this mod.
    @chdloc for teaching me about biQuads.

    XDA:DevDB Information
    Audio Mod, Tool/Utility for the OnePlus One


    Version Information
    Status: Stable

    Created 2018-03-12
    Last Updated 2018-03-21
    Cần you port maxxaudio to oreo :D
    I'm not developing anymore for the oneplus one as I'll replace it. I bought xiaomi mi 8 today for wich I'll probably make a stereo mod again.
    My oneplus served me 3 years, but part of my touchscreen isn't working anymore after one drop too much.. ?
    Holy **** man, this is awesome!
    The very very best implementation I have ever Seen of Earphone for stereo.
    Totally upgrades experience. Many thanks for keeping my OPO so relevant and alive.

    The bass is also way better than anything I achieved with Viper4Arise.

    Thank you very much for sharing !

    Working great , real upgrade .

    Great to hear!
    You could leave a thumbs-up on the first post to encourage me to make more developments ?

    it works perfect.you can manual replace the mixer_paths.xml from /system/vendor/etc.great job.

    Oh I see, the location of mixer_paths.xml has changed with android 8.1...
    I'll update the installer to support android 8.1. In the mean time, you could indeed manually replace the mixer_paths.xml like zzyyi66 said, but take a backup of the original because the uninstaller won't work if the installer can't make a backup.
    For the people who manually replaced it without making a backup: another way to return to stock would be dirty flashing your rom again.
    Initial publication.

    Added istaller support for android oreo.