So here’s the story of how to connect your electric guitar or bass to an iPhone, iPod touch, or iPad via the headset interface.

We’ve been considering this issue since as far back as 2008: GuitarToolkit customers have long been asking for a way to tune their electric guitars and basses without needing to power up an amp. We looked into what it would take and started building prototypes in 2009. At around the same time, the lightbulb went off: “Wow, if we could connect an electric guitar as input to an iPhone, and still have headphone audio coming out, we could do some really interesting things …” and this eventually led to our forthcoming AmpKit app.

Today, after a full 10 generations of prototypes, we’re thrilled to be collaborating with Peavey Electronics on the commercial realization of our explorations: AmpKit LiNK, a guitar and bass interface that, paired with AmpKit, bring full-scale amp and effects simulation to iPhone, iPod touch, and iPad users. (AmpKit LiNK is available for preorder here.)

OK, so let’s look at the challenges of interfacing a guitar through the iPhone’s headset connection. One *could* simply rig up an adapter cable that would connect a guitar signal to the iPhone headset input, and a headphone jack to the iPhone headphone output; our first prototypes did just this, and there’s even a commercial product made this way. But you would encounter a number of problems.

1- The iPhone will (possibly intermittently) fail to detect that an audio device has been plugged in to the headset jack. The iPhone is looking for the electrical signature of its earbud headset, which includes an electret microphone. A guitar signal directly connected to the mic input is very different electrically; in our experience, a directly-connected guitar signal will “kind of work sometimes,” which can be a highly frustrating experience.

2- The incoming guitar signal will suffer severe attenuation of its high frequencies, resulting in an awful, muddy sound. This is again due to the different electrical characteristics of the guitar signal versus the electret microphone the iPhone expects.

3- You’ll get really nasty feedback if you try to use headphones with a high-gain guitar amp simulation. The issue is that, in the cable between the iPhone and the interface, the faint, low-current guitar signal runs right alongside the comparatively high-current headphone signal, using a common ground. The result is that the outgoing headphone signal bleeds onto the incoming microphone signal, a phenomenon known as crosstalk. Now, if you happen to be simulating an amplifier on your iPhone, especially a high-gain amp like a Peavey ValveKing® or 6505® Plus, this crosstalk turns into the ugly screech of feedback.

Over the course of our 10 prototypes, we grappled with each of these problems in turn. Here’s how we solved them in the AmpKit LiNK interface:

#1: The failure-to-detect problem requires a bit of circuitry such that the iPhone sees the electrical characteristics it expects with the earbud headset’s electret mic. Result: immediate and consistent detection of the connected interface by the iPhone OS.

#2: The muddy sound issue involves a more significant set of circuitry, which transforms the guitar signal such that it has the signal characteristics of an electret mic to the iPhone, while at the same time preserving the full frequency spectrum of the guitar signal. The result: a very nice, rich guitar signal which sounds great when run through an amp simulator.

#3: The toughest nut to crack was the feedback issue. We found that using a well-shielded cable between the interface and the iPhone was not by itself enough. Instead, we had to tackle the heart of the problem: the high current levels needed to drive headphones. We incorporated a tiny but powerful headphone amplifier inside the AmpKit LiNK interface itself, which enabled a radical reduction in the current flowing between the iPhone and the LiNK. Between great cable shielding and the current-reducing benefits of moving the headphone amp inside the interface, feedback on high-gain amps is virtually eliminated. You can still cause feedback if you crank a super high-gain amp up to max volume, and do the same with your iPhone hardware volume control. But this is actually fairly realistic: a real amp would have feedback under similar conditions.

AmpKit LiNK is powered by two AAA batteries. Buyers of guitar interfaces should bear in mind that, if the headset guitar interface you’re considering isn’t powered (with batteries or an external power supply), you’re almost certain to have feedback problems when simulating high-gain amplification over headphones.

Also note — anyone who owns an iPad should consider cable length. AmpKit LiNK’s cable is long enough to connect to a docked iPad with the LiNK laying flat on the table. A shorter cable would leave the interface dangling off the side of the iPad, which is likely to result in an iPad crash of the physical variety.

Stay tuned to this blog as well as @AmpKit on Twitter for news on AmpKit and AmpKit LiNK. You can also send us your questions about AmpKit or AmpKit LiNK here.

Starting with an awesome team get-together at Yosemite National Park and highlighted by the honor of winning an Apple Design Award, this past week was certainly one to remember for Agile Partners.

When Apple announced in April that WWDC 2010 would take place June 7-11 at the Moscone Center in San Francisco, we immediately saw it as a must-attend event for Agile Partners. With the opportunity to learn more about the latest advancements in iOS technologies, take advantage of hands-on labs, and benefit from one-to-one interactions with Apple engineers, we knew WWDC 2010 would be an invaluable experience for our team as we continue to develop innovative applications for iPad, iPhone and iPod touch.

We kicked off our visit to northern California with a weekend get-together at Yosemite. The breathtaking views and tranquil trails (with an unexpected abundance of snow still on the ground) made Yosemite the perfect way to charge up for WWDC. To top it off, the talented chefs among the members of our team made sure everyone was well nourished with some incredibly tasty meals!

After driving from Yosemite back to San Francisco, our participation in WWDC started at 6:00 a.m. on Monday, June 7 as we lined up to attend Apple CEO Steve Jobs’ keynote address. The keynote address was filled with exciting announcements that culminated with the introduction of the new iPhone 4. Then, along with 5000 developers from around the world, we started digging into a wide variety of technical sessions and hands-on labs led by Apple engineers. Our team had come prepared with several questions related to our on-going projects and it was great to discuss them one-on-one with some of the 1000 Apple engineers attending WWDC.

The week was also packed with special events including awesome lunchtime presentations by speakers from Pixar, NASA and CNN. Evening activities included the perennially entertaining “Stump the Experts” Apple trivia event (hosted by some of the most knowledgeable and colorful Apple engineers you’ll ever meet) and the WWDC Bash at Yerba Buena Gardens with surprise musical guest, OK Go.

For our team, the highlight of the week occurred on Tuesday evening when Agile Partners was honored with a 2010 Apple Design Award for our TabToolkit for iPad app. We shared the stage with eight other developers whose applications also demonstrated technical excellence, innovation, superior technology adoption, high performance and outstanding design in the eyes of the Apple judges. It was a proud and humbling moment that inspired all of us at Agile Partners to keep working hard at continuously improving our craft.

We’re not a group that rests on our laurels — by now, we’ve all returned safely home and are preparing for some exciting days and weeks ahead. We’re at the beginning of Agile Partners’ most prolific period of product launches yet, with new products around the corner that we believe will delight our customers. Armed and energized by what we learned and experienced during the week of WWDC 2010, we’re ready to create many more memorable moments. Stay tuned!

Today, Agile Partners is proud to announce that our entertaining new app–Second Opinion, which you can use to ask any “yes-or-no” question, and get the “real answer” through crowdsourcing–is now available in the App Store.

What is it that got me thinking about developing an app like Second Opinion?  Focus groups.  You know, the kind where someone is paid to interact with or critique someone else’s work.  These studies can be great, providing multiple, anonymous and–most importantly–unbiased data points from unrelated 3rd parties.  The kind of responses you can’t get get as easily from co-workers, employees, or consultants; where politics cast shade, even when there’s the best of intentions.

Having designed and participated in a number of these studies, one “gotcha” is–because for the participant, this is not an anonymous experience–participants sometimes feel social pressure to answer a particular way. To seem smarter, for instance.  A common focus group observer “trick” is to “watch what they do, not just listen to what they say,” to compensate for this effect.   Remove all relationships between the “asker”, “answerer” & “moderator”, and the truth finds its way to the surface more easily: the model behind Second Opinion.

So, let’s make it personal–I have questions. Usually it’s about something outside of my areas of expertise (I’m better with power tools than picking outfits; I can critique the heck out of a film, but won’t know if the wine I choose will offend my vinofile friends).   I wanted my own focus group … and Second Opinion became my tool for everyday crowdsourcing.   The wisdom of the crowd provides the “real answer” (i.e., what is commonly perceived to be true) in a way that friends and experts–by their very nature–may not.

And, while Second Opinion can be a really useful tool for getting others’ opinions  in a crowdsourcing sense, we learned something else about it: it is an absolute blast to use!  Both answering questions and asking questions is addictive fun.  We’ve put together a few videos to show you just how much fun:

We’re very excited about the Second Opinion launch, and are curious to see what people will ask–and learn.  Why not give it a whirl: download Second Opinion from the App Store (free, with optional in-app purchases).

I think it’s safe to say that this is one of the most exciting times ever at Agile Partners. TabToolkit for iPad (App Store link) just launched and is featured on the the App Store under “New and Noteworthy iPad Apps.”   We really believe TabToolkit will transform how people learn, practice and enjoy playing their favorite songs on guitar, piano, drums and other instruments.

Far more advanced than the basic sheet music viewers that simply display PDF or image files, TabToolkit is the only app that can smoothly render entire pages of crisp, engraved music in standard or tablature notation, on-the-fly.  You can see TabToolkit for iPad in action in this YouTube video.

We redesigned TabToolkit specifically for iPad to take full advantage of the unique features of the revolutionary device — the large display, Multi-Touch interface and incredible speed. It’s amazing how smoothly you can scroll through music with TabToolkit on iPad or jump to any point of a song by simply tapping or dragging the music on the screen. We think musicians will really enjoy viewing crisp, sharp music notation on the high resolution iPad screen.

Already one of the highest-rated music apps for iPhone, TabToolkit also enables users to listen to and control the audio of individual instrument tracks. Being able to control the audio of individual tracks makes it really fun to practice music with TabToolkit. For example, you can mute the guitar part of a song you’re learning while being guided by the bass, keyboard and drum parts playing in the background. It’s like you’re playing along with an entire band.

While other guitar tablature apps available for iPad and iPhone display only text tabs, TabToolkit fully supports “rich tabs” that include multiple instruments and the ability to hear an entire song performed. Similarly, while a few sheet music apps have appeared, these simply scroll static images or PDF pages. Because TabToolkit understands the underlying music, it accurately renders music on-the-fly in any notation, page size and orientation. TabToolkit also simultaneously renders perfectly synched multi-track audio for the song, including effects like guitar bends and slides.

TabToolkit supports text, PDF, Power Tab and Guitar Pro file formats (Power Tab and Guitar Pro files are required to experience TabToolkit’s full visual and audio capabilities). The app also has easy-to-use file upload and download features, enabling users to take their music with them wherever they go.

TabToolkit for iPad is already getting a lot of attention, particularly on Twitter. For example, @jimsylee tweeted “TabToolkit for iPad is looking veryyy nice”, @ayapejian said “TabToolkit looks great on the iPad, time to throw out all my printed guitar tabs – very happy!” and @gbevin said “TabToolkit for iPad looks mindblowing!!”  And the folks over at Mac|Life have already posted this TabToolkit for iPad article.

We’re proud that we’ve successfully tackled many tough challenges with TabToolkit, but what’s most important is that our customers enjoy our apps, find them useful and provide feedback to help us continuously improve them.  That’s Agile Partners’ commitment and what we’re focused on.

We’re excited (and a bit surprised) to report that Star6 1.1 has hit the App Store –  a quicker-than-expected approval of the update has left us scrambling a bit! This is a substantial release, many new capabilities, but for my money, the #1 new feature is quantizing; specifically, quantizing when you jump from one sample to another.

Jumping between samples is a core activity when you’re jamming out with Star6.  In release 1.0, you had to hit the sample button at exactly the right instant to keep your music “on the beat” … tough to do, even for experienced DJs. In Star6 1.1, jumping between samples is automatically quantized. You simply select what beat interval you want to quantize on, from 1/16th of a beat up to 4 beats. Then when you jump from one sample to another, Star6 automatically delays the jump so that your sound stays lined up on the beat interval you selected.

Besides keeping you lined up on the beat, quantizing also makes it possible to easily alternate between two samples, playing, for example, 6 beats from sample A followed by 2 beats from sample B, and back again. For me, this one feature makes Star6 1.1 a huge improvement.

Another big win in 1.1 is a raft of BPM-related changes. First of all, we’ve put the BPM control right on the main process screen. This control works in three different modes. First, you can touch the + or – buttons to move up or down a single beat at a time. Next, if you touch and hold, you get “alarm clock mode” where the BPM moves up or down faster the longer you hold. And finally, we’ve added a very nice scrubbing mode: if you touch and hold the BPM button, then move up or down, BPM follows that movement. So you can move from 120 BPM to 303 BPM in a split second by moving your finger up an inch — fun!

Also new on BPM is the ability to control whether pitch varies with the BPM change. Previously Star6 always used granular synth magic to keep the pitch the same, but in 1.1 you can toggle it so pitch varies up and down with the BPM. This can produce some great effects (think James Brown as fast chipmunk) but also causes less distortion when you modify the BPM on certain types of music. For example, if you’re working with the ambient loops from FM3’s Buddha Machine, BPM changes work much better in “vary pitch” mode.

Previously, Star6 would force all samples within a session to run at the same BPM. In Star6 1.1, you can now vary the BPM for each sample. This is helpful when you’re working with samples that are less beat-driven than the typical club / dance music — again the Buddha Machine samples come to mind. And finally, we’ve added a tap-to-BPM bar on the options screen, so you can easily match speeds with the music you’re listening to.

One more notable change to Star6’s control interface is around the reset button. Star6 has always had reset, which returns the six granular synth settings back to their starting (neutral) position. In 1.1, the reset button has been expanded to also reset effects and reversing; so if you have a sample playing with synth effects plus DSP effects plus running in reverse, a single tap of reset puts everything back to neutral. What’s even more powerful in 1.1 is that, if you tap reset again, it “un-resets”: that is, all those processes and effects you just turned off are turned back on in a single click. This makes some really amazing toggles possible, from wildly crunched to original sample, back and forth, just by toggling reset.

We’ve added support for downloading and installing entire sample packs in a single click, via Mobile Safari or from within Star6’s News area. We did this by registering a custom protocol, star6://, when the app installs. If you then click on a star6:// link within Mobile Safari, it automatically loads Star6, downloads the sample pack, and creates a new session for those samples. The format of a sample pack isn’t complex, just a zip file with the samples and some optional metadata, so you can publish your own star6:// downloads if you choose to.

You’ll notice a fairly significant change to Star6’s look and feel in 1.1. We had a chance to sit down and walk through Star6 with Apple’s Eric Hope, an iPhone User Experience Evangelist, at the recent Tech Talk in Seattle. Eric enjoyed Star6’s rather unique and non-standard styling and colors, but suggested a more rounded, 3D look. We’ve taken Eric’s advice and think you’ll like the results. We’ve also cleaned up many other aspects of the UI and UX, particularly the session listing screen.

All in all, in our most humble opinion, Star6 1.1 is twice as much fun! Let us know what you think.