Basics
MIDI controller versus a keyboard that makes sound
A keyboard-shaped MIDI controller can look like an instrument while doing a different job. It sends performance information—notes, timing and often control changes—to something else. That something else must generate the audible sound.
The controller role
When a key is pressed, a controller can transmit a MIDI note event, along with velocity information when the model supports it. Knobs, wheels, pads, switches and faders may send other MIDI messages. A computer can receive those messages through a USB connection and use them to control a software instrument or digital audio workstation. An external synthesizer can receive MIDI through a five-pin DIN cable or another supported connection.
The sound role
A software instrument generates audio in a computer or tablet. A hardware synthesizer or sound module generates audio in the external device. A digital piano or keyboard workstation may have its own tone generator and audio outputs. These are different product functions; a MIDI controller does not gain an internal sound engine merely because a bundle includes software sounds.
MIDI is not audio
A five-pin MIDI cable carries control messages, not the sound from a synthesizer. A MIDI Out connection from a controller to an external instrument must be paired with the external instrument's audio connection to headphones, speakers or an audio interface. Similarly, connecting a controller to a computer with USB does not guarantee that the computer has a sound source, compatible software or the desired monitoring route.
Make a simple signal diagram
- Controller keys or pads send MIDI.
- A USB host or MIDI device receives the messages.
- Software or an external sound engine generates audio.
- An audio output or interface sends sound to headphones, monitors or a recorder.
Before buying, check each link in the chain and the power source for each powered device. A product page that lists USB and MIDI Out tells you about its controller routes; it does not by itself prove an audio output, speakers, battery operation or included sustain pedal.