Ok, there's already plenty of information on the web about the important stuff your new keyboard should have so I'm not going to re-invent the wheel here. Suffice to say, my list of 'must haves' are:
1. Velocity (touch) sensitivity for dynamic playing.
2. Full sized keys
3. A minimum of 61 keys (5 octave span)
If you're not sure of what any of this means go googling!
What I want to cover today is the stuff behind the keyboard that doesn't often get talked about. Yep, those funny little round jacks on the keyboard's rear panel. What you'll find (or don't find) here is a good indicator of whether you're buying a toy or something that will keep you in the game for a good while. So let's get started!
1. Sustain (or Hold) Jack - This is where you attach a sustain pedal available from music stores for around $30-$50(AUD). Do not attach anything here other than a sustain pedal or risk causing serious damage to your equipment. Many have found out the hard way! A sustain pedal simulates the action of the damper pedal on an acoustic piano which moves the dampers away from the strings and allows them to vibrate freely. Sustain pedals are one of the most overlooked add-ons for a keyboard and are useful for creating full and rich sounding arrangements.
2. Expression Jack - Attach an expression pedal here. This allows you to control aspects of the sound (commonly volume) using your foot. You'll find an expression jack on many synthesizers, organs, stage pianos, and higher-priced electronic keyboards. Expression pedals are great for live performances when you need to accent certain parts without having to reach for the volume control.
3. USB Port - This port allows communication of 'events' to and from external devices connected to it via a standard USB cable. It's definately worth paying a little extra for this option as it will keep you ahead of the game for longer. By attaching a laptop or tablet you can trigger the sound generated by the device's app using your keyboard's keys and controls. There are literally thousands of awesome sounding apps out there which can greatly expand your sound palette - many of which are free. A great way to make a cheap keyboard 'sound' expensive without the high cost!
4. MIDI (Musical Instrument Digital Interface) Ports - These provided a similar function to USB ports before the USB standard was created. It's important to note that MIDI does not carry audio, only controller and note data called events. If the keyboard you're thinking about buying doesn't have a USB port make sure it has these.
5. Line Out allow connection to a home stereo or external monitor speakers using an audio cable(s). A keyboard's internal amplifier and speakers are often constructed with cost and portability in mind so connecting it to more expensive outbound gear can greatly improve the sound - particularly the bass response.
Finally a Headphone jack is useful for some quiet practice time.