Can You Hear Me Now?
First things first: Some Apps require microphones. iPhones are equipped with built-in mikes, but iPod Touch users will need an external microphone. Apple offers a version of their white earbuds with a built-in mike (Apple Earphones with Remote and Mic, $29). Prefer to use you own headphones? Plug them into the Griffin SmartTalk ($19.99), a compact mike that clips onto clothing or instruments for a high-quality signal. Don’t plan on using headphones at all? Try ThumbTacks by SwitchEasy ($12.99), an ultra-compact mike that really puts the “micro” in microphone.

Instrumental Vocab
The App Store has several programs to help you brush up on scales and chords. While most seem to be guitar-oriented, ScaleMaster ($9.99, RoGame Software) works for all musicians. Its library holds more than 100 scale types in every key, displayed on a staff in treble, bass, tenor, or alto clefs. The entries can also be shown on a virtual guitar, bass, mandolin, or piano. Scale degrees in relation to the root are shown, too.

Planet Waves also offers two excellent reference apps for guitar, ChordMaster and ScaleWizard (both $1.99).

Boom-Tap Boom-Tap
DigiDrummer ($1.99, Magnick Software) features a similar interface as Beat-Maker, but it’s better suited as a finger-tapping pastime than serious software. It’s not programmable, so what you play is what gets recorded and it’s difficult to tap out clean beats on an iPhone’s small screen. You can play along with your music library, however, and the 27-drum kit sound library is worth its price. It’s available as a one-drum kit Lite version for free and a 99-cent eight-drum kit Micro version.

Remember the drum program on the App Store TV commercials? It was Drum Kit ($1.99, Crimson Jet, Inc.), another cool percussion program, but laid out like a drum kit rather than a drum machine.

Block Rockin’ Beats
The small screen format might have you fooled, but BeatMaker ($19.99, Intua) is high-quality sequencing software. It won’t replace a more serious sequencer or laptop in a live performance setting, but works great for on-the-go composing. BeatMaker comes with a large, multi-genre sound bank that you can expand to your heart’s content using your own samples. The interface is intuitive, the audio is crisp, the playback is low latency, and you can move files between your iPhone and computer with ease, using a free companion program. This App is the real deal.

Tuning Up
Most tuning Apps work like digital pitch pipes—they produce a reference note that you tune to. Cleartune ($2.99, bitcount) is much more versatile. It’s a microphonebased chromatic tuner, as well as a pitch pipe, and works for any pitched instrument. It allows you to calibrate notes, transpose keys, and even supports solfège notation. Advanced enough for a pro and simple enough for amateurs, this program is a best bet.

The aptly named Guitar Tuner by Alvin Yu. It emits reference pitches for standard tuning only, but its free.

Timing Is Everything
Tempo ($.99, Frozen Ape) is probably better than your standalone digital metronome and definitely costs less. It even compares to $89 programmable metronomes. This App counts in 17 time signatures and up to six rhythmic patterns, in tempos ranging from 20 to 220 beats per minute. You can save your rhythmic configurations with the setlist function and pull them up later at a rehearsal. Pulsating lights keep the beat if the background gets too loud.

Also check out Metronome by MarketWall.com. It’s free, though very light on `features compared to Tempo.