Tuesday, 16 March 2010

Guitarbud™ Review

The recent news that PRS Cables have brought out a cable to attach your guitar to your iPhone and iPod Touch was good news for RiotMode. We have been working on our guitar multi-effects software, RiotFX, for quite some time in the hope that a commercially available cable or adapter would come to the market and allow users to jack their electric guitar directly into their phone.

Before Guitarbud™, the only ways to attach your guitar to your phone were through some pretty funky adapter arrangements, some homebrew soldering projects or a tinny headset microphone dangling near your guitar. None of these solutions where good enough in our view!

So down to the Guitarbud™. As far as I know, it’s the first product to market that addresses this problem, and it will make lots of people happy. But it does have shortcomings…

The cable is pretty much a basic breakout cable – splitting a 4-pole TRRS plug for the iPhone/iPod Touch into a ¼” mono plug and a 3.5mm stereo headphone jack, and so its quite steep at $29.

Guitars aren’t supposed to be plugged directly into an iPhone or iPod Touch: The iPhone expects the presence of an electret microphone, with a constant DC resistance of about 3Kohm and with output levels much below that of guitar pickups. An electric guitar really needs to be plugged into a high impedance load. A good guitar amp will have a load impedance greater than 1Mohm, much more than that of the iPhone.

The upshot of this is that the guitar will overdrive your iPhone (which can be corrected by adjusting your guitars volume pot) and produce a ‘muddy’ sound due to the low impedance iPhone input acting as a lowpass filter. The aforementioned adjustment of the volume pot can also do funny things to the phone (remember it expects a constant DC resistance) – turning the volume pot to 0 (breaking the circuit) and then back up (remaking the circuit) can make your iPhone/iPod think that you’ve clicked the control button on your headset and cause it to start playing your iTunes collection!

Thankfully there is a solution to this problem: Inserting an inline impedance matcher between the Guitarbud™ and your guitar. Impedance matchers are used to plug a guitar directly into a mixing desk, and they do a good job here too. Unfortunately most have an XLR socket on the low-impedance side so you might need an XLR plug to mono jack adapter too.

Cross Talk
There is one other problem with the cable, and that is cross talk. Unfortunately, the cable used is quite thin and therefore I suspect that there is insufficient shielding to stop cross talk. You basically have a microphone wire carrying a small electrical signal running right next to headphone wires carrying a strong electrical signal for a couple of meters. When you turn your iPhone’s volume up the headphone wire induces a signal in the microphone wire and you get feedback – especially when using an application such as RiotFX, which has very low latency. Keep your volume down if you experience this!

RiotFX is available for purchase now on the AppStore for $4.99 in the US and £2.99 in the UK.

More information on RiotMode and RiotFX can be found on the RiotFX website.

More information on the PRS Guitarbud™ can be found here.


  1. Is it possible rather that to output to headphones to output to an amp w/ adapters? Would the signal be strong enough?

  2. Yes that is possible. You'll need a 3.5mm male-male adapter and a 3.5mm female to 1/4" male adapter.

  3. AFAIK -- the iPad is capable of USB audio input (and output too maybe?)...I purchased one on the off chance that someone would use this feature to develop a nice guitar multieffects program for the ipad. Do you guys see this as being helpful or do you think that no one will want to take advantage of it since it requires the camera connection kit?