Random Quantized Drum Pattern Generator

Description

Generate caller-defined percussion lanes on a fixed integer subdivision grid with Bernoulli hits, inclusive MIDI velocities, explicit rests and delegated quarter-tempo/PPQN timing; no audio, MIDI file or percussion-map assumptions.

A musical fixture expresses pitch or timing through explicit numeric conventions such as MIDI numbers, semitone intervals, beats, and durations. A reproducible symbolic sequence is separate from a performed sound or a judgment of musical quality.

When to use this tool

Use this generator to create reproducible drum pattern cases from the supplied model or bank. Inspect the returned evidence before using cases in a test or exercise.

How to use the tool and how it works

Supply bars, meterNumerator, meterDenominator, subdivisionsPerQuarter, pulsesPerQuarter, beatsPerMinute, lanes, minimumVelocity, maximumVelocity in the field shapes below. Set seed when you need an explicit replay.
Run the tool and correct any input error. For generated controls, distinguish a successful fixture containing an invalid case from failure to generate the fixture.
Read lanes, velocityGrid, hits, totalSteps, totalTicks, stepDurationSeconds, durationSeconds, microsecondsPerPulse. Use the conventions below. Keep answer-bearing fields separate when presenting an exercise.

Derive a finite step grid from meter, bars, and subdivisions. Draw each lane's hit flag and positive velocity, convert steps to ticks and nominal seconds, and return the velocity matrix plus time-ordered hits and MIDI clock timing.^[1]

Delegated operations used for this result: midi clock us per quarter ppqn. Their calculation or parsing conventions apply to the corresponding result fields.^[2]

Input field	Meaning and units	Accepted input
bars	Bars	Required. Safe integer; minimum 1; maximum 16.
meterNumerator	Meter Numerator	Required. Safe integer; minimum 1; maximum 16.
meterDenominator	Meter Denominator	Required. Safe integer; one of 1, 2, 4, 8, 16.
subdivisionsPerQuarter	Subdivisions Per Quarter	Required. Safe integer; minimum 1; maximum 24.
pulsesPerQuarter	Pulses Per Quarter	Required. Safe integer; minimum 1.
beatsPerMinute	Beats Per Minute	Required. Finite number; strictly above 0.
lanes	Lanes	Required. Array of Object; no unknown keys.; minimum items 1; maximum items 16.
lanes[].id	Literal identifier used independently of display labels.	Required. Text; minimum UTF-16 length 1; maximum UTF-16 length 64.
lanes[].midiNote	Midi Note	Required. Safe integer; minimum 0; maximum 127.
lanes[].hitProbability	Hit Probability	Required. Finite number; minimum 0; maximum 1.
minimumVelocity	Minimum Velocity	Required. Safe integer; minimum 1; maximum 127.
maximumVelocity	Maximum Velocity	Required. Safe integer; minimum 1; maximum 127.
seed	Optional numeric seed; takes precedence over context randomness. Without either, use the fixed tool.io default seed.	Optional. Safe integer.

Output field	Interpretation	Returned shape
lanes	Lanes	Required. Array of Object; no unknown keys.; minimum items 1; maximum items 16.
lanes[].id	Literal identifier used independently of display labels.	Required. Text; minimum UTF-16 length 1; maximum UTF-16 length 64.
lanes[].midiNote	Midi Note	Required. Safe integer; minimum 0; maximum 127.
lanes[].hitProbability	Hit Probability	Required. Finite number; minimum 0; maximum 1.
velocityGrid	Velocity Grid	Required. Array of Array of Safe integer; minimum 0; maximum 127.; minimum items 1; maximum items 4096.; minimum items 1; maximum items 16.
hits	Hits	Required. Array of Object; no unknown keys.; maximum items 4096.
hits[].laneId	Lane Id	Required. Text; minimum UTF-16 length 1; maximum UTF-16 length 64.
hits[].midiNote	Midi Note	Required. Safe integer; minimum 0; maximum 127.
hits[].step	Step	Required. Safe integer; minimum 0; maximum 4095.
hits[].tick	Tick	Required. Safe integer; minimum 0.
hits[].onsetSeconds	Onset Seconds	Required. Finite number; minimum 0.
hits[].velocity	Velocity	Required. Safe integer; minimum 1; maximum 127.
totalSteps	Total Steps	Required. Safe integer; minimum 1; maximum 4096.
totalTicks	Total Ticks	Required. Safe integer; minimum 1.
stepDurationSeconds	Step Duration Seconds	Required. Finite number; strictly above 0.
durationSeconds	Duration Seconds	Required. Finite number; strictly above 0.
microsecondsPerPulse	Microseconds Per Pulse	Required. Finite number; strictly above 0.
randomness	Replay source and normalized 32-bit seed, or null seed for an advancing context source.	Required. Object; no unknown keys.
randomness.seed	Optional safe-integer replay seed; normalization and precedence are explained below.	Required. Safe integer. or Null.
randomness.source	Source	Required. Text; one of "context", "seed".

An explicit safe-integer seed takes precedence over injected context randomness and is normalized to an unsigned 32-bit integer. With no seed and no context source, replay uses the fixed tool.io default seed. A context source must return finite values from zero inclusive to one exclusive; its advancing state must be retained separately. randomness records the source and normalized seed, or null for context. These generators are not cryptographic random sources.

json

{
  "input": {
    "bars": 1,
    "meterNumerator": 4,
    "meterDenominator": 4,
    "subdivisionsPerQuarter": 2,
    "pulsesPerQuarter": 24,
    "beatsPerMinute": 120,
    "lanes": [
      {
        "id": "kick",
        "midiNote": 36,
        "hitProbability": 0.6
      },
      {
        "id": "snare",
        "midiNote": 38,
        "hitProbability": 0.3
      }
    ],
    "minimumVelocity": 60,
    "maximumVelocity": 100,
    "seed": 42
  },
  "output": {
    "lanes": [
      {
        "id": "kick",
        "midiNote": 36,
        "hitProbability": 0.6
      },
      {
        "id": "snare",
        "midiNote": 38,
        "hitProbability": 0.3
      }
    ],
    "velocityGrid": [
      [
        0,
        94,
        0,
        81,
        85,
        0,
        70,
        0
      ],
      [
        0,
        0,
        80,
        0,
        0,
        79,
        0,
        84
      ]
    ],
    "hits": [
      {
        "laneId": "kick",
        "midiNote": 36,
        "step": 1,
        "tick": 12,
        "onsetSeconds": 0.25,
        "velocity": 94
      },
      {
        "laneId": "snare",
        "midiNote": 38,
        "step": 2,
        "tick": 24,
        "onsetSeconds": 0.5,
        "velocity": 80
      },
      {
        "laneId": "kick",
        "midiNote": 36,
        "step": 3,
        "tick": 36,
        "onsetSeconds": 0.75,
        "velocity": 81
      },
      {
        "laneId": "kick",
        "midiNote": 36,
        "step": 4,
        "tick": 48,
        "onsetSeconds": 1,
        "velocity": 85
      },
      {
        "laneId": "snare",
        "midiNote": 38,
        "step": 5,
        "tick": 60,
        "onsetSeconds": 1.25,
        "velocity": 79
      },
      {
        "laneId": "kick",
        "midiNote": 36,
        "step": 6,
        "tick": 72,
        "onsetSeconds": 1.5,
        "velocity": 70
      },
      {
        "laneId": "snare",
        "midiNote": 38,
        "step": 7,
        "tick": 84,
        "onsetSeconds": 1.75,
        "velocity": 84
      }
    ],
    "totalSteps": 8,
    "totalTicks": 96,
    "stepDurationSeconds": 0.25,
    "durationSeconds": 2,
    "microsecondsPerPulse": 20833.333333333332,
    "randomness": {
      "seed": 42,
      "source": "seed"
    }
  }
}

Limitations and assumptions

PPQN must divide cleanly by subdivisions and total steps/ticks must fit budgets. The result is symbolic data, not a MIDI file, synthesized audio, or a guarantee of rhythmic or instrumental suitability.
A replay requires the same complete input and implementation. The stated sampling convention applies within its eligible space. A finite draw does not exhaust all possible outputs; repeats remain possible unless a distinct-selection rule is explicit.
The field tables state structural bounds; cross-field constraints and bounded search or output budgets also apply. Unknown keys are rejected where the object contract disallows them. Input errors are distinct from null fields and deliberate invalid controls in a successful output.

Alternative or Complementary methods

For a supplied example, inspect the returned construction or delegated check directly. To evaluate a consumer, also test cases chosen for its own boundaries; a generated finite corpus does not establish exhaustive coverage.

References

Tool behavior and example: Random Quantized Drum Pattern Generator — tool.io
Calculation or validation: music/midi-clock-us-per-quarter-ppqn — tool.io

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