[ROOT] Stereo Audio Recording Nexus 6
On to the details:
The Nexus 6 has three microphones. The main microphone sits behind the lower speaker grille. The other two have their ports open toward
the back of the phone, i.e. one of them near the USB port and the other one near the camera lens. For camcorder recordings, the Nexus 6 uses
the front microphone by default.
This mod changes two system files, i.e.
/system/etc/media_profiles.xml and /system/etc/mixer_paths.xml.
While the changes in media_profiles.xml simply enable two-channel processing, the more interesting changes occur in mixer_paths.xml.
After some experimentation, we have found that the microphone close to the USB port is associated with ADC1 (channel one of the analog-to-digital converter in the audio codec), the microphone close to the rear camera is associated with ADC4, and the main microphone is associated with ADC3.
The mixer file now contains a new audio device called camcorder-stereo (only called when the "camcorder" device is requested)
that uses the
microphone by the camera lens as the left channel and the microphone close to the USB port as the right channel. The gains are kept at stock
camcorder levels, i.e. ADC1=ADC4=8. These gains are by no means set in stone. You can adjust them as you like, making the microphone more or
less sensitive in the process. Indeed, you may need/want to do that when you plan on recording, say, a club visit or rock concert.
Keep in mind, though, that you need to reboot your phone anytime you make changes to the mixer_paths.xml file as
the new values are read only upon a system boot.
Welcome side effect: In addition to the camcorder now being able to capture stereo audio, all audio recording apps that allow the microphone
to be changed to the "camcorder" microphone (provided the app itself offers stereo processing) can take advantage of this mod, too.
Apps that are capable of recording stereo audio with this mod are "Voice Recorder" and "Easy Voice Recorder Pro".
Installation:
- make a backup of your stock media_profiles.xml and mixer_paths.xml files (attached in the "stock" archive for convenience)
- manually push the two files in the "stereo_mod" archive to /system/etc/
- adjust the permissions of the two files to 644 (rw-r--r--)
- reboot
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