They do promise a professional audio solution with this version. Even though it seems to me that things is working really well on some devices already. But this will be more generally on all devices that will use Android O (what sweet starts with o?).

Here is what they say about audio:
AAudio API for Pro Audio: AAudio is a new native API that's designed specifically for apps that require high-performance, low-latency audio. Apps using AAudio read and write data via streams. In the Developer Preview we're releasing an early version of this new API to get your feedback.

To read the whole thing:
https://android-developers.googleblog.com/2017/03/first-preview-of-android-o.html

The most exciting audio news is that midi will be easier for developers to implement.
​So maybe some of the standalone synthesizer apps will turn midi on Marshmallow as there is some decent ones that is without midi or sequencer. But to be honest some of the best apps have already implemented midi with their own solutions...
The Audio will also be of higher quality...

To read more about Marshmallow go here:
https://www.android.com/versions/marshmallow-6-0/

and here is a list of the devices that will be updated so far:
http://lifehacker.com/every-phone-thats-getting-updated-to-android-marshmallo-1734676576

This is an older application but it is still a very good application. Perfect for controlled chaos glitchy type of rhythms to record and reuse. It is also deeper than can be suspected at first glance. 
Android Experiments is a Google project with free experimental applications and this is the first music app on that page. Most of it being graphic  in nature. 

To see the other apps if you missed my post about this page before:
https://www.androidexperiments.com/

Here is what is said on the website:

Develop a sweet spot for Marshmallow: Official Android 6.0 SDK & Final M Preview


By Jamal Eason, Product Manager, Android

Android 6.0 Marshmallow


Whether you like them straight out of the bag, roasted to a golden brown exterior with a molten center, or in fluff form, who doesn’t like marshmallows? We definitely like them! Since the launch of the M Developer Preview at Google I/O in May, we’ve enjoyed all of your participation and feedback. Today with the final Developer Preview update, we're introducing the official Android 6.0 SDK and opening Google Play for publishing your apps that target the new API level 23 in Android Marshmallow.

Get your apps ready for Android MarshmallowThe final Android 6.0 SDK is now available to download via the SDK Manager in Android Studio. With the Android 6.0 SDK you have access to the final Android APIs and the latest build tools so that you can target API 23. Once you have downloaded the Android 6.0 SDK into Android Studio, update your app project compileSdkVersion to 23 and you are ready to test your app with the new platform. You can also update your app to targetSdkVersion to 23 test out API 23 specific features like auto-backup and app permissions.

Along with the Android 6.0 SDK, we also updated the Android Support Library to v23. The new Android Support library makes it easier to integrate many of the new platform APIs, such as permissions and fingerprint support, in a backwards-compatible manner. This release contains a number of new support libraries including: customtabs, percent, recommendation, preference-v7, preference-v14, and preference-leanback-v17.

Check your App PermissionsAlong with the new platform features like fingerprint support and Doze power saving mode, Android Marshmallow features anew permissions model that streamlines the app install and update process. To give users this flexibility and to make sure your app behaves as expected when an Android Marshmallow user disables a specific permission, it’s important that you update your app to target API 23, and test the app thoroughly with Android Marshmallow users.

How to Get the UpdateThe Android emulator system images and developer preview system images have been updated for supported Nexus devices (Nexus 5, Nexus 6, Nexus 9 & Nexus Player) to help with your testing. You can download the device system images from the developer preview site. Also, similar to the previous developer update, supported Nexus devices will receive an Over-the-Air (OTA) update over the next couple days.

Although the Android 6.0 SDK is final, the devices system images are still developer preview versions. The preview images are near final but they are not intended for consumer use. Remember that when Android 6.0 Marshmallow launches to the public later this fall, you'll need to manually re-flash your device to a factory image to continue to receive consumer OTA updates for your Nexus device.

What is NewCompared to the previous developer preview update, you will find this final API update fairly incremental. You can check out all the API differences here, but a few of the changes since the last developer update include:

• Android Platform Change:
  • Final Permissions User Interface — we updated the permissions user interface and enhanced some of the permissions behavior.

• API Change:
  • Updates to the Fingerprint API — which enables better error reporting, better fingerprint enrollment experience, plus enumeration support for greater reliability.

Upload your Android Marshmallow apps to Google PlayGoogle Play is now ready to accept your API 23 apps via the Google Play Developer Console on all release channels (Alpha, Beta & Production). At the consumer launch this fall, the Google Play store will also be updated so that the app install and update process supports the new permissions model for apps using API 23.

To make sure that your updated app runs well on Android Marshmallow and older versions, we recommend that you use Google Play’s newly improved beta testing feature to get early feedback, then do a staged rollout as you release the new version to all users.

Seems like a nice iniative from Google and there is some interesting looking applications already. Unfortunately no Sound/music apps yet and all of them more or less graphical in nature. 

Here is what is said on the website:

JOIN US IN A CELEBRATION OF CREATIVITY AND CODE ON ANDROID.Android was created as an open and flexible platform, giving people more ways to come together to imagine and create. Developers everywhere have used the unique capabilities of the platform to push the limits of what’s possible on phones, tablets, watches and beyond.

We’re working to document creative experiments like these and make them open source so anyone can see how they are made, or get inspired to create their own. Our hope is to encourage more developers to challenge how we interact with the devices we use every day.

Each experiment is submitted by the creator, and all kinds are welcome—no matter your skill level, the framework it uses or the device it runs on. If you’ve created something amazing on Android you’d like to share, please submit your own experiment.
__________________________________________________________________________________________________
To see what apps have been made (and they all seem to be free) and so on:
https://www.androidexperiments.com/

Just like Audiotool another online Daw that sometimes gets mentioned it does not have anything directly to do with Android but it is possible to use over your device if you have good internet connections and use Chrome as your web browser.
So the business model is that you are limited to how many numbers of projects that you can have going and strangely enough in number of drum kits...
There is a free subscription though where there is five projects available to work on. 

It does not come with much in form of sound generators.
So far there is only one basic synthesizer and audio loops available!
Coming with a number of effects though.
But the strength of the application is the possibility to record audio tracks 
and have direct collaborations.
So for bands that live far apart to compose or start collaborations with other people signed up it is great but like said not really with virtual instruments.
To mention to is that everything is stored in the cloud so you can jump from device to desktop etc.
Soundtrap are part of this video from Google I/O 2014 as can be seen here:

Here is a video demonstrating the live recording in action:

Picture of the effects available.

To sign up:
https://www.soundtrap.com/

Not much of a music app post but as it is something that have excited me since Virtual Reality finally is getting here after Oculus Rift got announced a year ago or so.
God damn it I have been waiting for this since I tried a very basic Virtual Reality game with headset and tracking of movement in a amusement park at the end of the eighties. 
At the time reading Cyberpunk books obsessively and expecting it to be just another year or so to be flying around in all kinds of environments!
So it just took 25 years more until it finally is happening.
The problem being broke and it is going to take some time until I can get my hands on some Oculus rift glasses or the Sony version. 
Luckily enough there is some alternatives already and one of them being cardboard glasses that you can make yourself! 
It is surprisingly simple and there is a lot of room for your own inventiveness to modify or do your own design.
There is also to my surprise a bunch of apps to go with them. 
There is also two other cheaper glasses that you can buy.
Not only for games have been reading of a lot of different artist projects being made already and this is just the beginning. It is funny that just a year or so before Oculus rift got announced William Gibson wrote a novel taking place in the near future that had 
Virtual / Augmented reality used as art projects where you overlaid reality and 
being able for example see historical death scenes etc. 
Actually it is unlimited and games are probably going to be the least interesting aspect?
What this is going to mean for music making is not clear yet but one thing is to be able to visually be in the same space rehearsing, controlling Virtual entities on stage and at the same time be there on stage virtually or playing virtual instruments in the air for example. Something that already exists is virtual classes where you can overlay your own hands on top of the teacher.
Well this could easily turn into rambling without end so it is better to end it here and just post a video from Google talking about their cardboard glass project and then post links for further exploration.

Links:
Google Cardboard page
Google Cardboard app
Refugio 3D glasses
Durovis Dive Glasses

 This video is covering all the interesting new features in a short video which is nice as there is a lot of video material out there. Not too much about the audio but it is supposed that with the next Android version the latency is going to be around 20 ms.
Ahh and they bring up the cheap Google version of Oculus Rift in Cardboard that I will write about in the next post... as have been planned since some days.

These videos deal with new improvements on music making over the net but it is also optimized for being able to use your device for doing it. Think that it is very interesting if I only had more than one Giga for faster internet on the mobile contract...

Found this article that will let you know exactly what is going on with Audio and the new Android version coming. 
Ahhh so now there is no need to look through endless videos to get to the details.
GO here and read all about it!
http://geeknizer.com/audio-improvements-in-android-5-0-l-audiophile/

Ahhhhhh... Three hours of talkity talk! 
But I guess I should be seeing it ahhhhhh...
But my brother and his girlie is visiting and beer and suchlike...
But that does not stop you from finding out what Google is planning for Android?

Seeing that the Caustic artist Caustic Replay was releasing one album called Inception on Google Play was looking into it a little bit more as this year Musical Android will start to release music. It could be interesting but it is hard to tell how many people would use their Android devices to download music? 
The initial cost is 18.5 € / 25 $ to set up your page but that being the only cost independently how much music you put up. Then they will take a 30% commision on your sales unless you let it for free. Think that Google could have been a little bit more generous with the commission maybe 15-20 % would have been better for both the artists and for Google if they want to compete with other similar services.
Another hmmm from me would be that it is not for all countries. 
For example China, India and central and South America (Mexico yes) is not included... 
In either case if you are going to publish your music it can be worth a look?
Plus of course you should go and take a listen to Caustic Replay and if you can support!

Links:
Google Play Artist Hub
Caustic Replay album

Rej the developer of Caustic wrote this on the forum for Caustic and it could be interesting if you need as low latency as possible.
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I just finished finished the rather long process of flashing the Google Play edition ROM onto my stock HTC One (GSM version aka M7) and it made a noticeable difference on latency. I haven't taken any measurements, but it's probably somewhere around what the second-gen Nexus7 is getting. (and probably on par with the Blackberry Z10)

Yay! makes it worth the hour I spent..Go Google!

Addition:
This when using the OpenSLES sound API, which is only in Caustic 3 
(and many other audio apps on Android), but not in Caustic 2.
Oh, and also I stress that this is after flashing Google's vanilla AOSP ROM.
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Yes of course I know about rooting the phone  but did not think or have been aware that you can change the Operating System of your phone to what different manufacturers use. If you did not know this I think it can be interesting to be aware of the possibility. What it means is that even if you have An Android version like for example Jellybean or whatever every company has it's own proprietary system on top of that.
 Well as a Samsung phone would come preloaded with certain applications and their own versions of things.
Almost all manufacturers do not care too much about lowering the latency but Google is trying and working on it so now the lowest latency you can get is with Google's own Android version that comes with their devices. So if your phone has the same Android version as on a Google device you can switch to the same preloaded version of Android...As Rej did. Meaning that your phone would as in the case above turn into a Google Nexus device.
Have been thinking about doing this but have not had the need to lower the latency on my device yet...
Feeling tempted as there is a coming more and more midi enables synthesizers but as I am not much of a keyboard player and being a little bit afraid of doing something wrong...
If I understand it, it is not exactly like rooting your phone... but kind of fucked up an earlier phone trying to root it so if I do not get suddenly very good at keyboards probably will keep my device as it is and hopefully make some money soon so I can buy a Nexus 7 instead with lower latency already.
Here is some more information if you find this interesting:
http://highonandroid.com/android-roms/what-is-aosp/