The OPPO Digital HA-2 has been out for some time now and it already does that and it's not only sold in Japan.
https://www.oppodigital.com/KnowledgeBase.aspx?KBID=107&ProdID=HA-2
I plan to also post this to our Blog here: http://blog.moon-audio.com/
But will also post in this thread.
USB Digital Connection Issues for Android and Apple devices.
Until the release of
LollyPop 5.0 OS, the only way to get your Android Tablet or Phone to output digital audio was by the use of an OTG cable in unison with an App like USB Audio Player http://www.extreamsd.com/USBAudioRecorderPRO/. However, even with this app, all phones were not capable of connecting to an external Dac for audio playback. The USB Audio Player app will allow you to output USB digital audio to a USB Dac, but this is limited to audio stored on the device and played through the App ONLY. This App will not let you output audio from such streaming services as Tidal or for movies, etc. In order to use Tidal and output audio via the USB, the OS had to be updated for it to work. At last, LollyPop 5.0 OS has been released and it will now allow you to output digital audio from streaming services, movies or other applications. However, not all older generation Android devices can be updated and there are still some compatibility issues.
First, What is an OTG cable?
Why it is required for an Android device to output digital audio?
This is essentially a USB cable with internal conductors configured slightly different than a standard USB cable. This different configuration tells the android device whether it is to be a host or slave to the device on the other end of the cable. It sends a command to switch the iOS device to USB Host mode and after this USB role switch, the accessory switches its mode to a High speed USB Audio Device and tells the Android that this cable is to be used for passing a digital signal output. The Dac becomes the host device in this instance and this is very similar to the way Apple lightning cables work when connecting to dacs.
The previous Android OS 4x does not include a USB Audio Driver which is why USB Audio Pro had to be used.
Android OS 5.x: includes USB Audio Class 1 driver which runs at Full Speed (12Mbps)
USB Audio Player Pro App: includes 2 drivers, USB Audio Class 1 for Full Speed and USB Audio Class 2 for High Speed.
These 2 drivers embedded in the App communicate with the Dac chip to process audio. The Dac chip must also have the ability to work with each one of these drivers. In almost all cases, a Dac chip can work with one or both drivers.
However, here is where compatibility issues can arise. When listening to music via the Tidal Streaming service which uses 16/44.1kHz PCM over USB, OS 5.x is required by Tidal to provide the USB Audio Driver. But, Android devices with 4.x OS are unable to pass a digital audio output from Tidal as Android 5.x does not use both drivers like the USB Audio Pro App. OS 5.x operates using the Class 1 driver only so if your USB Dac does not have the ability to communicate with both Class 1 and Class 2 drivers you may not be able to connect to Tidal streaming services.
This digital audio compatibility issue is also common with Apple iDevices.
The Apple cables that use the Lightning Device Mode Chip do not allow High res audio output without the help of an App like SONY Walkman App or ONKYO HF Player. These Apps are needed because they use USB Audio Class 2 drivers in unison with an Apple Coprocessor embedded in the cable circuit of the to tell the Apple iDevice to output digital audio.
The iQube V5 portable headphone amplifier and Dac is one of our favorite portable USB Dac’s under $1000. It has a plethora of digital inputs, an analog input and it will decode almost all digital formats including DSD audio. However, it does not have USB Class 1 driver support so while it works flawlessly with USB Audio Pro App, it will not work with Tidal since Android OS 5.x does not have USB Class 2 driver support. Android did not include both drivers in their iOS software is surprising & hopefully, this will change in the future. If you’re going to do an update, make sure it is not already behind the curve as it is not that difficult to add this.
The Chord Hugo uses X-MOS firmware to support USB Audio Class 1 and defaults to Full Speed, thus they will work with Android OS driver. Both Tidal and USB Audio Pro App work with the Chord Hugo so it does not have compatibility issues.
I am sure there are other examples and this might be a good thread for folks to add this valuable advice. We don’t sell every device on the market so we can’t test everything but I will be happy to add to this post if I receive email verification that a particular piece does or does not work. The same can be also done on Apps that have dual driver support.
Now to explain Apple digital connection issues which are complicated.
Until now, all Apple iDevices that utilize the Lightning connector to USB A performed in
USB Device Mode Audio. The type of USB connector on the end of a Lightning cable tells you whether it is a USB Device Mode Audio cable. In this connection type between a Dac and Apple iDevice, the Dac works as a USB Host and the iOS device works as a USB slave.
Apple calls this mode 'USB Device Mode Audio'.
This mode supports Full Speed (12Mbps), 16bit/32,44.1 and 48kHz PCM audio. But a Dac can send a USB Switch request like a USB On The Go command to switch iOS device to USB Host mode. This is similar to what happens with an Android OTG cable. After negotiation there is USB Role Switching. The Dac switches its mode to a High Speed USB Audio Device. Basically USB Class 1 and Class 2 driver support is now implemented. After this USB Role Switching, ONKYO HF Player App, for example, can recognize and send 24/192kHz PCM or DSD(DoP) data.
Problems going forward that I see with Apple.
Apple loves to change connections on their devices often like their switch from the 30pin Dock connection to the Apple Lightning connection on their 5th generation of iDevices.
However, Apple’s MFi team is putting the USB Role Switching into maintenance stage and it may not support with future iOS versions. We will check iPhone 6s and iPhone 6s Plus, once we have a chance to see if they have already gone in this direction very soon.
What does this mean?
This means that devices like the Oppo HA-2 that currently have the ability to connect 24/192 and DSD through the ONKYO HF Player App, may not be able to with future iOS updates. I am not certain on this but it is looking this way.
Apple is moving to is what is called USB Host Mode Audio protocol.
This new protocol will utilize Lightning to USB Mini B or Micro B connectors. The choice for these connections and why products have to go through MFI certification is to make sure that all products in the chain work with each other. Thus, MFI certified USB Dac’s that have USB A will not work with a USB Host Mode Audio protocol cable. If you put an adapter on these to convert to USB A, it will not work. Case in point, the Oppo HA-2 will not work with a USB Host Mode Audio protocol cable and an adapter.
We tried to get Apple to let us do a MFI certified USB Device Mode Audio protocol cable with USB mini B in order to have a cable available for the Cypher Labs newer products that use a female combo USB mini A/B combo connector. However, the only way to get a cable through certification was to use a Mini A connector.
Has anyone seen a USB mini A connector readily available?
I have not and I could not find a source anywhere. Plus, the expense we would go through to tool up for these for just a few devices was cost prohibitive so this option was abandoned.
Looking towards the future, Dacs will need to provide circuitry to adhere to USB Host Mode Audio protocol or having the ability to do higher resolution audio may fade into the background. They will still be able to do as they did in the past, 16bit/32,44.1 and 48kHz PCM audio but I cannot confirm all of this at the present. Knowing how Apple loves to mix it up & continues to find new ways to increase their royalty revenues, it is very possible that it will lead this way and only time will tell.
We know of only 2 devices that are currently using the USB Host Mode Audio protocol, the RAL-KEB03 and the Microshre G3.
Both work as a USB Audio Class 2 Device after starting up. We have the Prototype Ral here and are helping them fine tune the steps in the digitally controlled volume pot. The neat thing about USB Host Mode Audio protocol is that you can now use both the volume control on the portable Amp/Dac and the Apple iDevice to control the volume. This can make things easier when the phone is strapped to an Amp/Dac for on the go listening to provide easier control from the phone. With newer headphones that come with Apple controls on the cable, you will be able to control the volume from the Headphone cable. This cannot be done with USB Device Mode Audio protocol.
Lightning Host mode cables enable the iOS Lightning port to become a USB Host port same as MacOS X USB Host ports.
Apple recommends that USB Host Mode Audio and unified iOS USB Audio Drivers for MacOS X USB Audio to have implementation of iAP2 protocol compulsory with a MFi Logo Test that started in January 2015.
Hopefully this is not too confusing, as I merely scratched the surface on these 2 formats but hopefully this and future posts we make will enable you to make the right choice in what connection type you need. The confusion I feel is only going to worsen with more formats in the future and I don’t foresee any sort of industry standard either.
