Audiobus got a mysterious update yesterday with a new Measurement Mode option in the settings section. This is a feature that has been in iOS since 6, but is undocumented by Apple and misunderstood by developers. The only thing anyone can agree on is that it is a way to tell the audio processing in iOS to leave your recording alone. Otherwise it tries to "squash" things. The scope of this function is now being debated. Some are insisting that it is only meant to effect recording the physical mic, or anything plugged into the 3rd rail mic input on the headphone jack.

In my testing though I've seen and heard a difference when just recording from app to app in Audiobus. Or at least I'm pretty sure I have. It is subtle. Science is backing me up on this one though! When I took recordings of the same sequence into Ableton's Spectrum there is a noticeable bump in the bass frequencies. This is showing the Max amplification (peak) for frequencies after playing a short clip. There is a 12dB boost at the extreme low-end, and a noticeable hump in the center.

I spoke with developer Michael Tyson this morning to try to understand this all a bit better.

In iOS 6, Apple introduced a new audio session mode, identified by the internal identifier AVAudioSessionModeMeasurement. From their documentation:

When this mode is in use, the device does minimal signal processing on input and output audio

By turning on “Measurement Mode”, developers can choose to bypass this filter, which restores the bass response.

In Audiobus 2.1.2, when you turn on “Measurement Mode” you enable this setting, restoring bass. But what’s more, the setting applies system-wide and is “owned” by the first audio app to be launched – the same way the latency setting is controlled by Audiobus when you launch it first. That means when you enable it in Audiobus, it’s going to be enabled for every other audio app you use during the session, regardless of whether that app uses Measurement Mode itself.

Note that the setting only applies to audio that comes in via the headphone jack, not audio interfaces that connect via the lightning/30-pin connector. Those devices that attach via the lightning/30-pin connector don’t have the bass-squashing filter applied at all. But for those using input devices that do attach via the headphone jack, we think this setting’s going to result in much higher-quality recorded audio across the Audiobus ecosystem. Yay!

I was baffled by that last bit, because in my tests I could have sworn I heard a noticeable difference when recording apps through Audiobus. I asked Michael if he was sure about this...

Before today I didn't realise it was just a headphone jack, but Jesse [Sonosaurus] said that was all it affected. It makes sense, given that the rest is digital. Still, it's entirely undocumented by Apple; so it could be doing all manner of things we don't understand. Apparently Apple's engineers are really tight lipped about it, too, for some reason.

Good old tight-lipped Apple engineers! They keep entire industries of bloggers in business. I don't know. I think I hear a difference. I think Ableton's Spectrum sees a difference. Take a listen to this and let me know if you can tell the difference.

A couple of weeks ago I featured an impressive iPad performance that used skulls as percussion instruments. The Works released this Behind the Scenes video of the performance, revealing the magic and their ingenious use of Impaktor!

Video Description:

2 iPads, 3 animal skulls, 4 Cameras, 5 people.... Loopy, Impaktor, Vidibox, Audiobus, Turnado and Crystalline.. iPad controlled by an APC 40... This is a newer, edited version of the video that shows a bit more behind the controls... Check it out and share if you like...

Buy Impaktor on iTunes: $4.99

thesoundtestroom did a much needed demo of TC-Data, released earlier this month from the developer of TC-11!

Buy TC-Data on iTunes: $19.99

With hundreds of apps featured on the site, the noble Banjo has gone entirely ignored. Until now! Listen & Learn: Banjo offers a combination of notation, audio and video recordings to... listen and learn to play the banjo. This is on sale at an introductory offer of $2.

Listen & Learn: Banjo iTunes Description:

Learn bluegrass banjo by ear with Listen & Learn: Banjo!

Our easy to use method combines written notation and audio recordings so you're challenged to figure out notes and phrases by ear, but you still have a visual reference of where you are in the song.

Find the notes on your instrument, play them to your iPad, and you're rewarded with stars to unlock more difficult songs.

There are nine well known traditional bluegrass tunes included in Listen & Learn.

1. Boil Them Cabbage Down
2. Worried Man Blues
3. Cripple Creek
4. Angeline the Baker
5. Roll in My Sweet Baby’s Arms
6. Cotton Eyed Joe
7. Reuben
8. Nine Pound Hammer
9. Salty Dog

This is the perfect app for beginner to intermediate banjo players, and has everything you need to hone your chops, including:

• Instructional Videos
• Jam Tracks (with real instruments to play along with)
• Metronome
• Tuner
• Recorder

You also have the ability to speed up and slow down tracks, so you can more easily learn by ear and play along at different tempos.

If you're a banjo player looking to take your playing to the next level in a completely organic and efficient way, look no further than Listen & Learn: Banjo.

Buy Listen & Learn: Banjo on iTunes: $1.99 (On Sale, from $3.99)

I don't often post singles, but this one from Xopianoi is pure excellence. Using field recordings from Tulum and Merida, Mexico, reader Ben Johnson composed A Dream of Tulum on Samplr. He also used Audioshare, Drumjam, DM1, and Alchemy on the track.

The combination of elements here sounds like a cross between late Sneaker Pimps, Enya, and a generous helping of Ayahuasca.

Buy Samplr on iTunes: $9.99