[OnePlus 2 Original Android Development] anupritaisno1:
Explanation of what all the v4a options do

Master power -> to turn on/off the v4a effect

Force enable v4a (special v4a versions only!) -> force enables v4a

Playback agc -> attempts to maintain constant loudness across a track or a movie. Not recommended for everyday usage. Can totally ruin certs tracks. Use the "master gate (limiter)" instead for adjusting general output gain

FET compressor -> it's a compressor, duh. Google if you want to know what these do but the aim of this is to avoid distortion

Viper DDC -> just like the equaliser but it accepts biquad values in raw format. The values are accepted inside "vdc" files. Used primarily for headphone correction but you can generate your own and achieve a really smooth equaliser

Spectrum extension -> attempts to make lossy files sound like lossless files.

FIREqualiser -> just your equaliser. Remember that the equaliser is really good but useless if you are looking to reduce bass it sucks. Use the equaliser in jamesdsp if you want to reduce bass

Convolver -> takes input "irs" file. Basically a lossless file containing frequencies that are commonly audible taken in vacuum and then the effect is added to the audio. Remember that the convolver is literally reshaping your audio so a low quality irs will seriously ruin your experience

Field surround -> does what it says on the label. Output depends solely on the capabilities of the phone's DAC and AMP. On our device you'll only notice a subtle difference

Differential surround -> trash, just don't even bother. It just makes sure that there's a difference of 2ms between the left audio channel and the right audio channel. Totally ruins audio quality. If music sounds good after enabling this either your earphones are bad or there's some undiagnosed issue with your brain. In any case this is a really bad effect to enable and I advice looking away

Headphone surround: uses several well-known tricks to create a surround effect. Great for music but can totally ruin sound quality in movies by making voices sound robotic

Reverberation: adds reverberation (will be elaborated below)

Room size: size of the room to create

Sound field: how far does it feel the sound is coming from

Damping factor: assume the reverberation was partially absorbed by "walls" and damp the sound output

Wet signal: volume/intensity of the reverberation effect

Dry signal: boosts the non-reverberation effect

Dynamic system: for bass, try it out

Tube sound simulator: for simulating an old speaker where it sounds as if the audio is coming from a tube

Viper bass: if you remember using "maxxbass" on oxygenos 2.1 (maxxaudio stuff) it's exactly the same as that. It adds bass only when necessary

Viper clarity: a really good effect if used correctly but can ruin your music if you're careless. A double-edged sword. Use with care

Auditory system protection: it does what it says. It's basically the viper developer copying every auditory system protection code ever made and smashing it into v4a

Analogx: the ugliest and the worst effect to ever be created. Many people swear by it but it's total nonsense and ruins sound quality. It basically simulates harmonic distortion of some really expensive audio equipment and adds more distortion to the distortion your phone is already producing. This seriously ruins audio quality.

Master gate (limiter): will be elaborated on below

Channel pan: can shift the volume of the audio channels if your earphones are defective

Output gain: a slider that controls digital gain

Limit threshold: if the music suddenly becomes too bassy, treble or mids increase too much this controls the amount in decibels to reduce the sudden irregularity