MIDI monitor, controller and step sequencer

Each message gets a line: the time, the port, the channel, the raw bytes and what they mean — note names (middle C is C4 here; switch to C3 for Yamaha and Ableton numbering), controller names (CC 7 Volume, CC 64 Sustain Pedal, CC 74 Cutoff…), program changes with their General MIDI instrument, drum names on channel 10, pitch bend as a signed value with its size in cents, aftertouch, song position as bar, beat and 16th, and MTC quarter frames, which are put back together into a time code. SysEx shows the maker from its manufacturer ID and spells out the Universal messages: an identity reply gives the maker, family, model and firmware version. A running clock shows its tempo.

Filter by channel, hide the 24-a-beat clock and active sensing, pause, switch between time since the first message and the time of day, and copy or export the log. Record SysEx dump collects every SysEx that comes in (start it, then trigger the dump on the device) and Save .syx writes them to a file.

Play the keyboard with the mouse or a finger (slide across it for a glissando), or with the computer keys A W S E D F T G Y H U J K O L P ; — Z and X move an octave, C and V change the velocity. Notes that come in from a device light up green. Choose the channel, send a program change from the GM list with an optional bank, move the pitch-bend wheel (it springs back to the middle) and the mod wheel, and use eight sliders that you can point at any controller. Raw bytes sends hex you type (running status is allowed: 90 3C 64 3E 64 is two notes), and the SysEx box sends hex or a .syx file; Identity request asks the device to say what it is.

Sixteen steps by eight rows. Drums puts every row on channel 10 with General MIDI drum sounds (kick, snare, hats, clap, toms, crash); Melodic fills the rows from a scale and root note. Each row has its own note and channel (under Rows), each step its own velocity: click to turn a step on, or switch to Velocity and click to step through four levels or roll the mouse wheel over it. Set the tempo, swing (50 % is straight, 66 % a triplet shuffle), the pattern’s length and the gate (how long each note sounds).

Notes are sent ahead of time with timestamps — the page looks 100 ms ahead every 25 ms — so the timing comes from the browser’s MIDI scheduler, not from the page’s event loop. Send MIDI clock sends 24 clocks a beat with Start and Stop, so a drum machine or DAW can follow. Follow MIDI clock does the opposite: Start, Stop, Continue and Song Position from an input drive the sequencer, six clocks a step, and Arm plays on the next clock when the other end never sends Start.

Patterns are saved by name in this browser; the share link carries the current one.