FAILURE MAP
← Case archive

FA-81776 / MIDI event timing / Open access

Channel note message encoder with running status: channel range validated as zero-based · case 01

Channel 16 is rejected and channel 0 is accepted, producing a negative status value.

Verified by executionVariant 1 · 8 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The channel range check uses zero-based bounds while the encoder subtracts one from a one-based channel.

THE FAILURE

The channel range check uses zero-based bounds while the encoder subtracts one from a one-based channel.

Unsuccessful approach: Tightening the upper bound to 15 still rejects channel 16.

Case contract

Input [events, running_status] with events [kind, channel 1..16, note, velocity]. A note-on with velocity > 0 encodes as 0x90|(channel-1), note, velocity. A note-off (or note-on with velocity 0) encodes as 0x90|(channel-1), note, 0 when running status is enabled; otherwise as 0x80|(channel-1), note, velocity for an off and note, 64 for a velocity-0 on. With running status enabled, a status byte equal to the previous one is omitted. Invalid values return None.

Why this case matters

MIDI sequencers, file readers and synth drivers depend on exact event ordering and tick/time arithmetic.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    if not isinstance(x, list) or len(x) != 2:
        return None
    events, rs = x
    out = []
    last = None
    for kind, ch, note, vel in events:
        if not 0 <= ch <= 15 or not 0 <= note <= 127 or not 0 <= vel <= 127:
            return None
        if kind == 'on' and vel > 0:
            status, data = 0x90 | (ch - 1), [note, vel]
        elif kind in ('on', 'off'):
            if rs:
                status, data = 0x90 | (ch - 1), [note, 0]
            else:
                status, data = 0x80 | (ch - 1), [note, vel if kind == 'off' else 64]
        else:
            return None
        if not (rs and status == last):
            out.append(status)
        out.extend(data)
        last = status
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[([[['on', 1, 60, 100], ['off', 1, 60, 40]], False], [144, 60, 100, 128, 60, 40]), ([[['on', 1, 60, 100], ['off', 1, 60, 40]], True], [144, 60, 100, 60, 0]), ([[['on', 1, 60, 100], ['on', 1, 64, 90]], True], [144, 60, 100, 64, 90]), ([[['on', 1, 60, 100], ['on', 1, 64, 90]], False], [144, 60, 100, 144, 64, 90]), ([[['on', 16, 60, 100]], False], [159, 60, 100]), ([[['on', 17, 60, 100]], False], None), ([[['on', 2, 60, 0]], False], [129, 60, 64]), ([[['on', 2, 60, 0]], True], [145, 60, 0])], [([[['on', 1, 60, 100], ['on', 1, 64, 90]], False], [144, 60, 100, 144, 64, 90]), ([[['on', 16, 60, 100]], False], [159, 60, 100]), ([[['on', 0, 60, 100]], False], None), ([[['on', 17, 60, 100]], False], None), ([[['on', 2, 60, 0]], False], [129, 60, 64]), ([[['on', 2, 60, 0]], True], [145, 60, 0]), ([[['off', 3, 60, 0]], False], [130, 60, 0]), ([[['on', 1, 60, 100], ['on', 2, 60, 100]], True], [144, 60, 100, 145, 60, 100])], [([[['on', 16, 60, 100]], False], [159, 60, 100]), ([[['on', 2, 60, 0]], True], [145, 60, 0]), ([[['off', 3, 60, 0]], False], [130, 60, 0]), ([[['on', 1, 60, 100], ['on', 2, 60, 100]], True], [144, 60, 100, 145, 60, 100]), ([[['on', 1, 128, 100]], False], None), ([[['cc', 1, 7, 100]], False], None), ([[['on', 10, 36, 127], ['off', 10, 36, 0], ['on', 10, 38, 127]], True], [153, 36, 127, 36, 0, 38, 127]), ([[['on', 1, 60, 1]], True], [144, 60, 1])], [([[['on', 1, 60, 100], ['off', 1, 60, 40]], False], [144, 60, 100, 128, 60, 40]), ([[['on', 16, 60, 100]], False], [159, 60, 100]), ([[['on', 0, 60, 100]], False], None), ([[['on', 1, 128, 100]], False], None), ([[['cc', 1, 7, 100]], False], None), ([[['on', 10, 36, 127], ['off', 10, 36, 0], ['on', 10, 38, 127]], True], [153, 36, 127, 36, 0, 38, 127]), ([[['on', 1, 60, 1]], True], [144, 60, 1]), ([[['off', 5, 70, 90], ['off', 5, 71, 90]], True], [148, 70, 0, 71, 0])], [([[['on', 1, 60, 100], ['off', 1, 60, 40]], False], [144, 60, 100, 128, 60, 40]), ([[['on', 1, 60, 100], ['off', 1, 60, 40]], True], [144, 60, 100, 60, 0]), ([[['on', 1, 60, 100], ['on', 1, 64, 90]], True], [144, 60, 100, 64, 90]), ([[['on', 1, 60, 100], ['on', 1, 64, 90]], False], [144, 60, 100, 144, 64, 90]), ([[['on', 16, 60, 100]], False], [159, 60, 100]), ([[['on', 0, 60, 100]], False], None), ([[['on', 1, 60, 1]], True], [144, 60, 1]), ([[['off', 5, 70, 90], ['off', 5, 71, 90]], True], [148, 70, 0, 71, 0])]]
for i, (args, expected) in enumerate(fixtures[N-1]):
    check("oracle %d" % i, solve(args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
oracle 0[144, 60, 100, 128, 60, 40][144, 60, 100, 128, 60, 40]Passed
oracle 1[144, 60, 100, 60, 0][144, 60, 100, 60, 0]Passed
oracle 2[144, 60, 100, 64, 90][144, 60, 100, 64, 90]Passed
oracle 3[144, 60, 100, 144, 64, 90][144, 60, 100, 144, 64, 90]Passed
oracle 4None[159, 60, 100]Failed
oracle 5NoneNonePassed
oracle 6[129, 60, 64][129, 60, 64]Passed
oracle 7[145, 60, 0][145, 60, 0]Passed

SHA-256 / eba8997af2a0ae0efb14b012d7fc5a182d0eba79e65fd9d8c06d66b7168d8a39

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    if not isinstance(x, list) or len(x) != 2:
        return None
    events, rs = x
    out = []
    last = None
    for kind, ch, note, vel in events:
        if not 1 <= ch <= 15 or not 0 <= note <= 127 or not 0 <= vel <= 127:
            return None
        if kind == 'on' and vel > 0:
            status, data = 0x90 | (ch - 1), [note, vel]
        elif kind in ('on', 'off'):
            if rs:
                status, data = 0x90 | (ch - 1), [note, 0]
            else:
                status, data = 0x80 | (ch - 1), [note, vel if kind == 'off' else 64]
        else:
            return None
        if not (rs and status == last):
            out.append(status)
        out.extend(data)
        last = status
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[([[['on', 1, 60, 100], ['off', 1, 60, 40]], False], [144, 60, 100, 128, 60, 40]), ([[['on', 1, 60, 100], ['off', 1, 60, 40]], True], [144, 60, 100, 60, 0]), ([[['on', 1, 60, 100], ['on', 1, 64, 90]], True], [144, 60, 100, 64, 90]), ([[['on', 1, 60, 100], ['on', 1, 64, 90]], False], [144, 60, 100, 144, 64, 90]), ([[['on', 16, 60, 100]], False], [159, 60, 100]), ([[['on', 17, 60, 100]], False], None), ([[['on', 2, 60, 0]], False], [129, 60, 64]), ([[['on', 2, 60, 0]], True], [145, 60, 0])], [([[['on', 1, 60, 100], ['on', 1, 64, 90]], False], [144, 60, 100, 144, 64, 90]), ([[['on', 16, 60, 100]], False], [159, 60, 100]), ([[['on', 0, 60, 100]], False], None), ([[['on', 17, 60, 100]], False], None), ([[['on', 2, 60, 0]], False], [129, 60, 64]), ([[['on', 2, 60, 0]], True], [145, 60, 0]), ([[['off', 3, 60, 0]], False], [130, 60, 0]), ([[['on', 1, 60, 100], ['on', 2, 60, 100]], True], [144, 60, 100, 145, 60, 100])], [([[['on', 16, 60, 100]], False], [159, 60, 100]), ([[['on', 2, 60, 0]], True], [145, 60, 0]), ([[['off', 3, 60, 0]], False], [130, 60, 0]), ([[['on', 1, 60, 100], ['on', 2, 60, 100]], True], [144, 60, 100, 145, 60, 100]), ([[['on', 1, 128, 100]], False], None), ([[['cc', 1, 7, 100]], False], None), ([[['on', 10, 36, 127], ['off', 10, 36, 0], ['on', 10, 38, 127]], True], [153, 36, 127, 36, 0, 38, 127]), ([[['on', 1, 60, 1]], True], [144, 60, 1])], [([[['on', 1, 60, 100], ['off', 1, 60, 40]], False], [144, 60, 100, 128, 60, 40]), ([[['on', 16, 60, 100]], False], [159, 60, 100]), ([[['on', 0, 60, 100]], False], None), ([[['on', 1, 128, 100]], False], None), ([[['cc', 1, 7, 100]], False], None), ([[['on', 10, 36, 127], ['off', 10, 36, 0], ['on', 10, 38, 127]], True], [153, 36, 127, 36, 0, 38, 127]), ([[['on', 1, 60, 1]], True], [144, 60, 1]), ([[['off', 5, 70, 90], ['off', 5, 71, 90]], True], [148, 70, 0, 71, 0])], [([[['on', 1, 60, 100], ['off', 1, 60, 40]], False], [144, 60, 100, 128, 60, 40]), ([[['on', 1, 60, 100], ['off', 1, 60, 40]], True], [144, 60, 100, 60, 0]), ([[['on', 1, 60, 100], ['on', 1, 64, 90]], True], [144, 60, 100, 64, 90]), ([[['on', 1, 60, 100], ['on', 1, 64, 90]], False], [144, 60, 100, 144, 64, 90]), ([[['on', 16, 60, 100]], False], [159, 60, 100]), ([[['on', 0, 60, 100]], False], None), ([[['on', 1, 60, 1]], True], [144, 60, 1]), ([[['off', 5, 70, 90], ['off', 5, 71, 90]], True], [148, 70, 0, 71, 0])]]
for i, (args, expected) in enumerate(fixtures[N-1]):
    check("oracle %d" % i, solve(args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
oracle 0[144, 60, 100, 128, 60, 40][144, 60, 100, 128, 60, 40]Passed
oracle 1[144, 60, 100, 60, 0][144, 60, 100, 60, 0]Passed
oracle 2[144, 60, 100, 64, 90][144, 60, 100, 64, 90]Passed
oracle 3[144, 60, 100, 144, 64, 90][144, 60, 100, 144, 64, 90]Passed
oracle 4None[159, 60, 100]Failed
oracle 5NoneNonePassed
oracle 6[129, 60, 64][129, 60, 64]Passed
oracle 7[145, 60, 0][145, 60, 0]Passed

SHA-256 / 52660e3266bf2105d1ff5e6c1dc07c6daa730c31db446c3ac17f44d9b2224236

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 8 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.

Member access is invitation-based. Sign in with your invited account to inspect the repair.

Sign in to the archive ↗

Verification & scope

A deterministic bounded teaching model with a stipulated toy contract; it is not a complete Standard MIDI File or MIDI 1.0/2.0 implementation. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:50:06.180478+00:00.

Case digest / cc0513fe958f718b86ddd352f1b3060f3f6c46ee74ed91a1da740c6887fea259