One of the HA-2's most impressive features is its ability to receive high resolution audio content from iOS devices without the use of the Camera Connection Kit.
Since the internal iOS Music application is limited to 24-bit, 48 kHz output, you will need to make use of 3rd party applications such as Hibiki (for DSD files only, $4.99 in the App Store) and Onkyo HF Player (for DSD and FLAC, WAV, etc. files, free in the App Store, in-app purchase required to enable high resolution playback).
In the example below, a DSD64 file is being played by an iPhone 6 running Hibiki connected to an HA-2 without the use of the Camera Connection Kit (CCK). The application is capable of either outputting the audio from this file as 352.8 kHz PCM or as 2.8 MHz DSD. The application supports up to DSD256.
In the example below, a 96/24 FLAC file is being played by an iPhone 6 running Onkyo HF Player connected to an HA-2 without the use of the Camera Connection Kit (CCK). The application reports that the audio is being output as 96 kHz PCM. When connected with most other portable DACs, this application will indicate a 48 kHz sampling rate unless the Camera Connection Kit (CCK) is utilized.
Since iTunes does not support high resolution audio files synchronized to iOS devices as music, you will need to sync the files using iTunes' File Sharing function. This is done by opening iTunes, selecting the music playback app under File Sharing in the Apps menu option, dropping the music files to the application's data window, and performing a sync. The example below shows a DSD track being dropped into the data window of the Hibiki app:
The way in which you utilize the HA-2's digital volume control depends on the device that you connect to the HA-2.
When an iOS device (iPhone, iPad, iPod Touch) is connected to Input A, the HA-2 informs the iOS device that it has hardware volume control capabilities and maps the iOS device's software volume control to the HA-2's internal, 32-bit volume control. Using this method, the iOS device still outputs bit-perfect audio and allows for finer volume control adjustment than what the HA-2's analog volume control provides on its own, without any degradation of audio fidelity. This is particularly useful with IEMs and other sensitive headphones.
For Android devices connected to Input B, you will need to utilize music playback software such as USB Audio Player PRO, which will allow you to indicate that a hardware volume control is available. Once the Android device's playback software is configured to recognize the HA-2's hardware volume control, it will output bit-perfect audio to the HA-2 and the Android device's volume control will be mapped to the HA-2's 32-bit volume control, allowing for finer volume control adjustment when using IEMs and other sensitive headphones.
When using full-sized headphones, it is recommended that you raise the volume control on the source device (iOS device, Android device, or computer) to its maximum level and use the HA-2's analog volume knob to adjust the volume.
Instructions for Computers Running Mac OS X
1. Connect the OPPO HA-2 to your computer.
2. Turn on the OPPO HA-2 and select input B.
3. Click on the Apple icon on the top left hand corner of the menu bar and select About This Mac.
4. Depending on the version of Mac OS X your computer is running, you will need to click More Info and then System Report, or if you are running OS X El Capitan, you can just click System Report, since the More Info button has been removed in that version. This will open the System Information application.
5. In the System Information application, click on the USB menu entry within the Hardware section.
6. In the USB Device Tree window, select the OPPO HA-2 USB Audio 2.0 DAC to verify the firmware version.
Instructions for Computers Running Windows
1. Ensure that you have already installed the OPPO USB Audio DAC driver on your computer (the latest version is available here: OPPO HA-2 USB DAC Driver).
2. Connect the OPPO HA-2 to your computer.
3. Turn on the OPPO HA-2 and select input B.
4. Open the OPPO USB Audio Control Panel application from the Start Menu under All Programs and select the Info tab.
5. The current firmware version will be displayed in the Revision field.