Re: how to access the sd card on Nexus 7
When you plug your Nexus 7 into a computer you should see many folders like Pictures (upload pictures here), Bluetooth, Download, etc. The media\audio folder is where I would put custom ringtones and notifications to match the organization of folders on the Android system folder (you will see below when doing the instructions). In My Computer it shows up as Nexus 7 > Internal Storage. If you have a screen lock, unlock your Nexus 7 or may have trouble accessing files, or viewing anything at all on the computer.
What you're seeing is your content as if the Nexus 7 had a SD card and not the systems content. In FileExpert this area is labeled as SD Card while the system guts are called Internal Storage. Reality is it is all one 8gb or 16gb chip.
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Multiple ways to transfer the stock audio notification files.
Wireless through computer browser with AirDroid
1. Install AirDroid on Nexus 7
2. Connect Nexus 7 to WiFi on the same network / router as computer.
3. Open AirDroid, in the Connection tab will be an IP URL address
http://XX.XX.XX.XX:8888
4. Access the IP URL through computer browser and type in the passcode.
5. Click Ringtones icon and you can view, play, or download all the audios from stock.
6. Check all and click Download. It will give you a Zip file.
You can also access by Files > collapse the Sd Card > expand System > system > media > audio
Right click or select files just like on a computer folder, then download.
NFC and Bluetooth with FileExpert:
I don't have an NFC phone to try it but I tested the Bluetooth way. You can browse files on your Nexus 7 with AirDroid but it doesn't show me the system folders like FileExpert does.
1. Install FileExpert on the Nexus 7
2. Open FileExpert go to My Files > Phone Internal Storage
(yes, my stock Nexus 7 displays Phone Internal Storage for the main Android system, and SD Card for the files, even though its all on one chip.)
3. Inside of Phone Internal Storage go to "system" > "media" > "audio". You'll see folders for alarms, notifications, ringtones, and ui. Inside are .ogg audio files.
4. Individually Transfer the files you want by touch and hold, then "Send files" > Bluetooth or NFC.
To Transfer the folders, go to "system" > "media" then touch and hold on "audio" folder and send via NFC. (Bluetooth did not show for transferring whole folder)