A Tasty Pixel » Audio

Four common mistakes in audio development

This is a discussion of [four common mistakes](#four-rules) that audio developers make, [how to do better](#solutions), and [how to detect whether there’s a problem](#diagnosis). It’s written primarily for developers, but should be accessible to non-developers too. I introduce [Realtime Watchdog](#diagnosis), a diagnostic tool for developers, and provide a brief [survey of popular audio libraries](#survey).

Making audio apps is enormous fun — it’s rewarding, there’s huge scope for creativity, and then when you’re done, other people use it to be creative too! There aren’t many fields that are like that, and I consider myself very fortunate to be able to work in this area.

But there’s also a serious side to working with audio. As audio developers we have a responsibility to our users to, basically, not embarrass them in public. A DJ whose equipment emits an ear-piercing crunch mid set will not thank us (well, it depends on the club. Maybe they will?). Nor will a performer whose backing drum machine clicks and crunches distractingly, throwing the performance. Same goes for in private — if the user just nailed a take, only to discover that there’s a giant click in the middle of the recording, they’re going to be cursing our name.

Now we’re living in a post-Audiobus/IAA world, where our users’ setups often span multiple apps, one bad actor can mess everything up, and it’s often impossible to tell from where the problem originates.

Imagine if Loopy HD had glitched in the middle of that?

The audio engineer on The Tonight Show told me the main reason that they chose Loopy for the looping segments with guests was because he had been a Loopy user for years, and it has always been solid and reliable.

Even if there’s just a one-in-ten-thousand chance that an app will glitch during a typical session, well, that’s one glitch a day if your app sees ten thousand sessions per day, which is not uncommon. Two glitches a day if it has twenty thousand sessions a day. And I’ll bet most music apps have a higher glitch rate than that.

It can take just one glitch during a live performance for a musician to completely lose faith in their whole setup. The one thing they cannot troubleshoot in their setup is their apps, because it’s an opaque system. And so every app they’re using is indicted. They’ll stop using all of them. It’s an angry Facebook post to all of their musician friends waiting to happen; the exact opposite of what anyone reading this would want.

So, it’s this duty of care that we audio developers have that I want to focus on in this article, because our music apps have to be solid and reliable. All of the time.

The Amazing Audio Engine 2 Sample App demo

Here’s a demo of the TAAE2 sample app – full source code with [The Amazing Audio Engine 2](https://github.com/TheAmazingAudioEngine/TAAE2).

Presenting The Amazing Audio Engine 2

Presenting The Amazing Audio Engine 2: a new audio engine for Core Audio. In this video I introduce the main concepts, and walk through creating a simple demo app that plays a loop with effects, mixed together with audio input, with recording capabilities.

Find TAAE 2 at [theamazingaudioengine.com](http://theamazingaudioengine.com), or on [GitHub](https://github.com/TheAmazingAudioEngine/TAAE2).

Thirteen Months of Audiobus: Part 2

This is the long awaited sequel to the tale of Audiobus’ development. I’m completing this article now, on the day we say an emotional farewell to our motorhome Nettle, who has today been sold to a new family in the UK. It seems like a fitting time to tie off some loose ends as we start the next chapter of our lives in our new home in Australia.

In [Part 1](http://atastypixel.com/thirteen-months-of-audiobus/) of this article, I wrote about the early stages of the technology which was to become [Audiobus](http://audiob.us), our inter-app audio platform, now supported by over 500 great music apps. Part 1 ended just as Sebastian had one of his genius moments, which I obnoxiously left as a cliffhanger. So, onwards:

It was winter in the south of France, and I was buried in the best kind of work: A new project, and one that brought together a bunch of different interests into a challenging, exciting heap.

But first, it was time to move on and find a more satisfying place to spend the rest of the winter.

Help! iOS 7 broke my microphone input!

We hear a lot about people having problems with their music apps on iOS 7 no longer receiving audio. I thought it was time I posted an article describing why this is happening, and how to fix it.

iOS 7 introduced a bunch of new security and privacy features and restrictions. In particular, when an app wants to record audio, iOS 7 will block the app from doing so until the user gives permission. Usually this happens via an alert dialog in the app:

However, if one taps “Don’t Allow”, the system won’t ask again — ever. That can spell confusion and frustration (and support emails, and 1-star App Store reviews!) for users who tapped the dialog away without reading it, and then discovered they’re unable to record audio.

Alas, there’s not much that can be done about that from our end, except for explaining how to fix the issue once this happens.

The trick is to open Privacy Settings for the device, and enable Microphone access for the app. The controls can be found in the system Settings app:

Once you’ve turned this on, the app should begin receiving audio. Depending on certain factors, you may need to [quit and restart](http://www.macworld.com/article/2048935/get-to-know-ios-7-multitasking.html) the app.

The Amazing Audio Engine is here, and it’s open source and Audiobus-ready

I’m very pleased to announce that [The Amazing Audio Engine](http://theamazingaudioengine.com) has pulled into the station. It’s been a long time in the making, and there have been one or two minor [distractions](http://audiob.us) along the way, but I’m proud of the result:

A sophisticated and feature-packed but very developer-friendly audio engine, bringing you the very best iOS audio has to offer. We’re talking audio units, block or object-based creation and processing, filter chains, recording and monitoring anything, multichannel input support, brilliant lock-free synchronization and rich Audiobus support.

You’ll find The Engine, a bunch of documentation and the brand-new community forum at [theamazingaudioengine.com](http://theamazingaudioengine.com)

It’s also [open source](https://github.com/TheAmazingAudioEngine/TheAmazingAudioEngine#license). And it’s ready for [Audiobus](http://audiob.us).

Thirteen Months of Audiobus

Tomorrow, Monday December 10, my friend and partner-in-crime Sebastian Dittmann and I are launching a project over twelve months in the making: Audiobus. We’re very proud of what we’ve managed to do, and we both firmly believe that Audiobus is going to fundamentally alter the way people create music on the iPad and iPhone.

You can find out more about Audiobus itself at [audiob.us](http://audiob.us), but I wanted to take a moment to breathe, look back, and explain why the hell I’ve been so quiet over the last year.

The Amazing Audio Engine: Funky Remote IO-based Core Audio Engine Coming Soon

Huzzah! I’m announcing a new project which will be launching over the next couple of months.

It’s called [The Amazing Audio Engine](http://theamazingaudioengine.com), and it represents the product of years of experience with iOS audio. It’s a sophisticated iOS audio engine that lets developers skip the Core Audio learning curve, and get on with writing great software.

The tech behind this is what drives [Loopy and Loopy HD](http://loopyapp.com), as well as the in-development [Audiobus](http://audiob.us) app.

[Subscribe at theamazingaudioengine.com](http://theamazingaudioengine.com) to be kept in the loop as it approaches launch time.

Some of the features:

Automatic mixing of multiple audio signals with per-channel volume and pan controls.
Built-in support for audio filtering and effects, including the ability to form complex filter chains, constructing channel groups, or even whole trees of groups, and filtering them as one composite signal.
Built-in support for audio input, including optional use of the Voice Processing IO unit, for automatic echo removal – great for VoIP.
Record or monitor the output of the whole audio system, for in-app session recording, or get the output of one channel, or any group of channels in the processing tree.
Support for any audio format (AudioStreamBasicDescription) that the hardware supports: Interleaved, non-interleaved, mono, stereo, 44.1kHz or any other supported sample rate, 16-bit, 8.24 fixed floating-point – whatever you need for your project.
Very light, efficient engine, designed from the ground up for speed. All Core Audio code is pure C; no Objective- C or BSD calls, no locks, no memory allocation.
Efficient mixing of input signals, using Apple’s MultiChannelMixer.
Fast, lock-free synchronisation mechanism, enabling developers to send messages to the main thread from the Core Audio context, and vice versa, without locking or memory allocation from the Core Audio thread. Message sending from the main thread is two-way, and can be asynchronous, with a response block, or synchronous.