I have a 7100nex and the audio quality of music from AA is just awful. I have the xtrememusic mod installed on my phone and use viper to fine tune the settings so over bluetooth or aux the sound quality is amazing.
I know I'll probably never be able to achieve that level of quality with AA since the head unit processes the audio, but does anyone have any recommended settings for the HU to improve the quality via AA?
What app are you using for playback? Streaming or local files? At what bit rate?
Generally, you are best to keep third party audio processors out of the path when it comes to using an android or IOS device as the source. These apps typically only use psychoacoustic methods to alter the sound, and introduce noise and jitter as a result. Try removing viper and see what results you get. See also:
http://geeknizer.com/complete-guide-to-android-smartphone-audiophile/
I stream at the highest bit rate possible from my subscription services, and I play .flac lossless files from the SD card slot when I really care about the source.
I haven't noticed any difference on my 8100 when playing Spotify on AA vs direct via Bluetooth, but I'll do some back to back testing today and report back.
I use Google Play Music with the files downloaded to the device. I'm using a Nexus 6, btw. I know it's just MP3, but should still be 320 kbps.
From what I understand, viper shouldn't be touching the audio files being sent to the HU anyway. If I disable it, it makes no difference in terms of quality.
Maybe I just need to play with the settings on the nex to get it sounding right, but left untouched the music sounds flat. No lows or highs. I'll download some flac files and see how that works as well.
I did some comparisons with Bluetooth direct and Android Auto, same track played from Spotify. I definitely confirm your observation, there is a distinct difference in audio quality between the two and with AA active the audio sounds flat. Ostensibly this would indicate that AA is affecting sound quality by altering the audio processing. I wont speculate how at this point, but this bears further investigation.
Does Google Play Music sound any better elsewhere? My experience was that the audio quality was very poor (unlistenable on my main system via Chromecast or Google TV), which is why I don't use it.