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

The Amazing Audio EngineHuzzah! I’m announcing a new project which will be launching over the next couple of months.

It’s called The Amazing Audio Engine, 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, as well as the in-development Audiobus app.

Subscribe at 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.
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Some updates to TPCircularBuffer

I’ve recently made some updates to TPCircularBuffer (on GitHub), my C circular/ring buffer implementation, which add a memory barrier on read and write, inline the main functions for a potential performance boost, and add support for use within C++ projects.

If you’re using TPCircularBuffer at all, I recommend updating!

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Circular (ring) buffer plus neat virtual memory mapping trick

I’ve just updated my C circular buffer implementation, adopting the trick originally proposed by Philip Howard and adapted to Darwin by Kurt Revis: A virtual copy of the buffer is inserted directly after the end of the buffer, so that you can write past the end of the buffer, but have your writes automatically wrapped around to the start — no need to manually implement buffer wrapping logic.

This dramatically simplifies the use of a circular buffer — you can use chunks of the buffer without any need to worry about where the wrap point is.

See the new implementation, which is thread-safe with one consumer and one producer, with no need for locks, making it perfect for use with high-priority Core Audio threads, on GitHub: TPCircularBuffer.

There’s a basic example of its use over on the original post.

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Equipment: Busking with Loopy on a Budget

Loopy user and forum member fonyo recently wrote an article on the Loopy forum about busking with low-budget equipment and Loopy. There was some great information in the article, so I’ve reproduced it here with some editorial modifications.

I’ve been planning for a long time to do some busking. I’ve always been amazed by street musicians, and can watch them for hours. That’s why I’ve put together some thoughts on buying portable equipment.

In summary: For just a fraction more money than that saved by choosing Loopy instead of a single Boss RC-300 Loop Station, you can pick up a complete, high-quality busking setup, perfect for going out into the street and performing for the public.

Boss RC-300 vs Loopy

First, let me compare the new Boss RC-300 Loop Station with Loopy, not counting the iPhone’s/iPad’s price (because we love it and would buy it anyway!). I chose the RC-300 as it gives you the closest number of individual loop tracks you can record/overdub

Item Cost Number of tracks
Boss RC-300 £400 + 3 stereo
Loopy £2 6 stereo
Loopy HD £5 6, 9 or 12 stereo

My point is this: let’s forget the RC-300 and save that 400 quid for other stuff to buy so we can go out and play!

Equipment list

Here’s my equipment list. I tried to find a balance between price and quality, while also keeping in mind portability.

Item Cost
Loopy £2 / £5 HD
iRig G&I interface ~£25
iRig MIDI ~£50
iKlip MINI ~£25
MOTU ZBOX ~£32
BEHRINGER FCB1010 ~£95
BEHRINGER XENYX 1002 B ~£74
PylePro PWMA series ~£100-200

Let’s see the details of each. Loopy is obvious, it’s the “core” in our iDevice and the iKlip is holding it (e.g. on a mic stand).

iRig guitar & instrument interface is transferring the sound to the iDevice.

iRig MIDI to control Loopy through MIDI (I know it’s not capable of doing this yet but soon it will be!) and we connect a nice MIDI foot switch (cheap and smart) the Behringer FCB1010. This is the only thing which needs a power supply but I’m listing it as I would go for it anyway. I’m sure now that iRig MIDI and LINE6 Mobilizer II are released we will soon find many battery-operated or maybe even passive foot-switches for iDevices through MIDI.

I’m sorry to disappoint you, but an electric condenser mic like the iRig iMic just won’t give you a nice sound, and as the tests and reviews are showing it’s just not suited for professional use such as live quality street busking.

That’s why I came up with an idea of a small but powerful battery-operated mixer with enough inputs to handle your better quality microphones. You can also plug in your instruments or any device with line out, such as an iPod as a music source.

The mixer device is the Behringer XENYX 1002B which runs on two (!) 9VDC batteries. The main output of the mixer (your gig) goes into the iRig’s TRS input. As a nice optional hardware for electric guitars with pickups, I recommend the MOTU ZBOX. It’s a miracle for guitar sound, and it’s passive so it doesn’t require any current. The Behringer 1002B has 5mic-line input OR 2mic-line/6stereo input with 3bandEQ, 2aux etc.

Finally, the Public Address (PA). I’ve found real luggage-like battery powered speakers made by PylePro and those are just wicked! Low-budget but nice stuff. They have wheels and handle for easy relocating, EQ, and many other cool things built-in. They give you enough power to blow away your own head with guitar riffs, beatbox, singing, so you can just use Loopy to amaze your audience! The iRig’s output goes in the PylePro’s input, and there we are.

You do need to buy a mic, but this way nearly anything will sound better than that electric condenser.

Summary

For the money you avoided spending on a Boss RC-300 LS for £400 (vs. Loopy 2 HD for £5), you can pick up nearly all this equipment — the sum is between 400-550 depending on where and what you buy or not. Then, you’re good to go and show some real busking to the public and start a career like our Uncle Dub Fx!

You can discuss fonyo’s research at the Loopy forum.

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