Using iPad/iPhone as guitar processor

Since the release of Guitar Rig, which was the first software I've tried and felt like a complete solution to use desktop/laptop as guitar effects processor. After I got my first iPhone 3G I believe it is a better device for process guitar, replacing traditional gears. Currently there are also a lot of hardware / software solution for this purpose. I will introduce the current solutions and also describe what I feel or what it should be in the future.

Methods of connecting guitar to iPad/iPhone

1. cables / adapters connecting to headphone minijack on iPad/iPhone

Several different headphone connectors are available to connect guitar to iPad/iPhone. However I found a similar problem exists in all adapter I've tried (more or less) - crosstalk feedback due to input output signals in the same cable. Therefore, the input signal volume, processing gain & iPad/iPhone output volume should not be too loud, or terrible feedback sound can come out very easily.

The best adapter in the market is AmpKit LiNK (from Peavey). It requires batteries installed which might be for buffering input signal to deal with feedback issues. iRig (from IK Multimedia) is also a nice choice but with the same price range I would recommend AmpKit LiNK.

I've tried PRS Guitarbud cable (seems discontinued), but found that the quality of the cable is not good enough. Griffin GuitarConnect cable looks like a similar item but haven't tried so not sure about the quality.

2. audio interface connecting to dock connector port of iPad/iPhone

There are also some products connecting to the dock connector port, providing guitar connection. In this way there should be no feedback issue which is mentioned above. Though these audio interface costs higher, they still worth the bucks since they provide better sound quality and you can achieve more processing gain without problems.

For iPhone, Sonoma Wire Works GuitarJack (not supported for iPhone 4) is the first solution I've seen. Apogee Jam is another neat interface (it can also be used with iPad and Mac) but it only provides input connection. I haven't tried them though since I live in Taiwan and it's hard to get these products here.

If you own an iPad and Camera Connection Kit, you can just use standard USB audio interface, however you might need a powered USB hub to provide enough power to the audio interface. I've tried a $20 USB audio interface designed for guitar and it is quite usable. But the connectors are very weak so it is not quite a solid solution for live use. It's still good for home practicing and jamming though.

Alesis just released iO dock which also looks like a pretty good interface for musicians, not only for guitarists.

Guitar Processing Apps

The 2 major apps on the App Store are AmpKit (from Peavey and Agile Partners) and Amplitube (from IK Multimedia). I personally prefer AmpKit for its brighter and more raw tone but the only disappointment I found is that it doesn't provide tap tempo for delay effects. Amplitube is also a good solution and it provides tap tempo, but the sound is just feeling too airy.

Both the apps provide free version for you to try first before you buy. However if you want to purchase Amplitube please beware that: Amplitube has separate apps for iPhone/iPad, and the in-app purchases are not shared in the 2 versions. This is really annoying customers especially those who own both iPhone and iPad. I suggest you to think which device you will use more often to process your guitar before you make purchase. Amplitube also released Fender version, so you should be again considering which you want (depends on whose App Icon you prefer, really) to be the base app and make in-app purchases for the remaining features…How annoying!

There are also some apps available for guitar processing like iShred Live.

For iPad you can also try Garageband. There's also an app on iPad called StompBox but it doesn't feel like a complete processing solution since it only provides preamp features instead of full amp & cabinet.

For Serious Live Use: Controlling / Switching

Currently the main way to switch presets in these guitar processing apps is by the touchscreen. It is hard to use when it is used for serious live situations. Griffin announced StompBox which looks like a nice switching solution for guitar apps.
Digitech just announced monstrous iPB-10 pedalboard for iPad but it is just too pricey for a controller…
I still believe the best way to control guitar processing apps is MIDI switch pedalboard through CoreMIDI. Currently only StompBox (for iPad) seems supporting CoreMIDI. There should be more apps supporting CoreMIDI control so standard MIDI controllers like Logidy UMI3, Moog MP201 and Behringer FCB1010 can be used with the software without explicitly support.