This is great information that is good for anyone that is interested in using Android for playing synthesizer apps live etc and for developers to have a look at...
It is compiled by the developers of n-Track one of the main DAW's for Android. That i salso one of the two that have the possibility to hook up an external USB sound card for low latency professional recording as well.

A big reminder to any developers that reads this...
They have developed Audioroute which brings interconnection between apps on Android.
It is free to use so please contact them so we can get the Android music eco system to the next level!!!
​https://audioroute.ntrack.com

Here is what they say regarding their latency tests:

Android devices audio performance chart
This page shows the latency calibration results performed by the n-Track Studio app. Results are collected anonimously.
Although the results are not scientifically accurate as each measurement is performed in different rooms with different acoustic conditions (as well as possibly different device volume settings), the results roughly represet the audio latency performance of various device.
We also show wether or not a device supports the FastPath, which is an optional feature of the Android audio system, which can help minimize audio latency when the app uses the recommended FastPath settings. "base" FastPath should allow for 45ms or lower latency, while "pro" FastPath should enable 20ms or lower latency. In the device detail page, for devices that support the FastPath, you can toggle between showing all results and only results obtained with the recommended FastPath settings.
We hope that this page will help orient users who care about realtime audio and want to identify devices that have good audio performance.
Latencies are measured in milliseconds.

And to see the results with clickable beautiful charts and suchlike:
ntrack.com/android-latency/devices

Now with some nice new effect plugins and other stuff...

Update:
n-Track Studio 9 is finally here. Here are the highlights of the new version:
- New Guitar amp plugin
- New Bass amp plugin
- New VocalTune vocal pitch correction plugin
- 3D spectrum view in EQ window
- Stereo image view in EQ window
- Redesigned user interface
- Echo depth can now be set as division of the song tempo
- Improved compatibility with USB audio devices

Woow. Look at that background.
Wonder if that is their office or it is the pace he lives in.
Guess n-Track Studio is doing good.

​They have in any case produced a series of tutorials that covers all aspects of the Android version of their DAW. Think that if anyone is looking for a Mobile DAW there is only two real options and that is n-Track and Audio Evolution Mobile. Both of them can use external sound cards and have all the basics covered when it comes to editing/mixing/effects etc. But the workflow differs pretty much and there is some basic other differences as well.
Both offers demo versions and recommend to test both as in the end it is a question personal preference. 

So to see the series of tutorials follow the video posted below...

So they have released a whole bunch of tutorials and there is some differences with the Android version but have big feeling that if going through them all someone will be fully educated in the ways of this mobile DAW.

This review is focused on the iOS version that is more or less the same but there is some differences to be aware of when reading...

To read the this in-depth review go here:
http://musicappblog.com/n-track-studio-review/

One in depth review delivered to the public, courtesy of Routenote.
So anyone interested in a mobile multitrack DAW go read here:
http://routenote.com/blog/n-track-studio-8-pro-mobile-daw-review/

So guess people did not like when n-Track Studio got released as subscription only so now it is possible to get it as before by paying a one time fee. The subscription model is still around though if there is a need to use it only once or twice etc.

Google Play:
https://play.google.com/store/apps/details?id=com.ntrack.studio.eight.pro

There is only two good multitrack DAW's for Android and this is one of them the other being Audio Evolution Mobile. Both of them being competent and good and most importantly both of them allow for USB sound cards to record with minimum (disclaimer; there is always some latency on any system digital or otherwise. Physical nature of things) latency.
There is differences between them that makes it worthwhile to inspect what is your preference.
Not going to list them as both apps have demos and would advice anyone to check it out for themselves plus the workflow is fairly different as well.

Anyway with this upgrade maybe the biggest difference is that n-Track Studio have started using a subscription fee instead. I am normally against it as I prefer to own the software but in this case it is kind of interesting as it probably not often that most people do serious recordings on their mobile devices as it is much more convenient to record on computer. But maybe the computer gets broken, a need to record your guitar playing cousin in hicksville or vacation etc it can be nice to just pay for a month?
​It is not too much, one euro for a basic subscription and two for a pro one.
The main difference is 32/64 bit export for the pro version instead of 16/24 bit for the basic. 
To be honest do not think that there is a high amount of people that can hear the difference between 24 bit and 32/64 bit.

So that means one euro a month instead of twenty or so which the older version cost and what more or less Audio Evolution cost with the goodies activated. 
So after doing the math and unless you need the higher bit rate plus Multichannel USB class-compliant audio interface and only use it for a month or two it becomes pretty cheap.

Ahh yes n-Track Studio also comes with the exciting song collaborating app SongTree incorporated. That could of course become addictive and costly in the end... after five years or so...

The owners of the older Pro version gets four months for free or just do not upgrade to avoid the subscription plan.

The update is:

n-Track 8 is here, with a lot of exciting new features!
- Step Sequencer: create beats, melodies and arpeggions
- Advanced Routing: record/bounce any track to an audio track
- Songtree integration: make music online with a community of talented musicians
- Improved MIDI and Audio editing: MIDI step recording feature, fade in/out curves and more
- Quick Grooves: instantly add drum and bass grooves to your project
- Export at high quality: export your song at 24 and 32 bits
- New and improved UI

Google Play:
https://play.google.com/store/apps/details?id=com.ntrack.studio.demo&pageId=107817317434258015023

If using Pure Data I guess this must be a DAW that would be highly interesting!
I asked n-Track Studio if it would be integrated into the Android version of n-track Studio as well and it seems that there is a possibility! 
That would be amazing as there is a lot of instruments and effects made already to be used even if there is no knowledge on how to use Pure Data. 
Songtree is also implemented directly into the DAW which is enticing if you are a user of Songtree on Android.

To read more about this affordable and capable DAW go here:
http://en.ntrack.com/index.php

This is the Youtube text:

Watch how you can use n-Track Studio for Android with the new Marshall London phone to record two tracks at the same time.
One of the peculiarities of the Marshall London is that it has two separate audio jacks, that allow plugging in two mics. 

In this video we used the standard headset that comes with the phone to record the harmonica, while we used a simple splitter cable to connect the acoustic-electric guitar output to the phone audio input and a set of standard (no mic) headphones as well, so that both players could hear what they've been playing.

On all platforms in which it runs (Windows, Mac, Android and iOS) n-Track Studio always allows to record from as many audio inputs as the audio hardware allows. On Android n-Track supports using external USB audio devices, but with the Marshall London there's no need for external devices to record two simultaneous tracks.

More info on the Marshall London phone here:
https://www.marshallheadphones.com/mh...

More info on n-Track at:
http://ntrack.com

Getting more serious with each update. 
It also comes with Midi out now, that is a very interesting option for anyone 
that want to use hir mobile device to control hardware synthesizers and other midi devices.
Would definitively recommend to use a USB Audio interface though, 
if you want to make some professional recordings with very low latency. 
Also would recommend to test the Demo version first to make sure everything works as expected on your device as it costs more than your average application and there can be some issues, me for example had the problem that it saw my usb soundcard as the microphone input and the 1/4 inch cable input as left and right mono inputs and not having any command that I could find for making the stereo track to mono leaving the recording totally panned to the left or right...
( This happens sometimes for me using Audio Evolution to, but not always... )
Could just be something specific just for my USB Audio interface though, it can also have been fixed now as the version I have is the one version previous that got sent to me to test in either case worth testing the demo version first.

The update:
___
- Midi Out
- Support for control surfaces (eg: Korg nanoKontrol2)
- Choose destination directory when saving projects, audio files and midi files
- Customizable back button behaviour
- Various bug fixes
___
Playstore link:
https://play.google.com/store/apps/details?id=com.ntrack.studio.pro

Android have a new contender as a serious portable DAW now. 
n-Track studio can now like Audio Evolution Mobile record low latency high quality audio through a USB soundcard.
It also have included General Midi instruments that you can sequence/record on midi tracks.
There is two options to buy n-Track Studio one cheaper version that have in-app purchases to chose from or the full version directly with all the goodness activated directly.
It is fully interactive with the desktop DAW that the company makes which am a very interesting cheap good alternative to more expensive DAW's.
Android is definitely moving forward!

Play Store info:
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• Support for USB audio devices, stereo & multichannel *
• not all devices are supported: USB compatibility chart available at http://goo.gl/R7l3Yb
• MIDI tracks with Piano-Roll editing window *
• Built-in General MIDI synth *
• Support for USB MIDI keyboards & controllers *
*Features available as in-app purchases
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Play Store Links:
n-Track Studio 
n-Track Studio PRO

Website with information about the Desktop DAW:
http://ntrack.com/