FA-10781 / PCM sample encoding / Open access

Unsigned eight bit silence center · case 01

Unsigned PCM silence is interpreted as a positive amplitude.

Verified by executionVariant 1 · 4 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Unsigned PCM silence is interpreted as a positive amplitude.

THE FAILURE

Unsigned PCM silence is interpreted as a positive amplitude.

Unsuccessful approach: Centering at 127 shifts every decoded sample by one.

Case contract

Decode unsigned 8-bit PCM byte integers into centered integer amplitudes by subtracting 128.

Why this case matters

A pure Python local audio pipeline stage with explicit sample formats and frame conventions; no real-time device or signal-spectrum claims.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(samples):
    return list(samples)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1',solve(*([0, 128, 255],)),[-128, 0, 127])
check('fixture 2',solve(*([128],)),[0])
check('fixture 3',solve(*([],)),[])
check('fixture 4',solve(*([127, 129],)),[-1, 1])
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 fixture	Actual	Expected	Outcome
fixture 1	`[0, 128, 255]`	`[-128, 0, 127]`	Failed
fixture 2	`[128]`	`[0]`	Failed
fixture 3	`[]`	`[]`	Passed
fixture 4	`[127, 129]`	`[-1, 1]`	Failed

SHA-256 / f96dde8e132a95e498227204762f239227bfee1d39c441630221452c4c8be552

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(samples):
    return [x-127 for x in samples]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1',solve(*([0, 128, 255],)),[-128, 0, 127])
check('fixture 2',solve(*([128],)),[0])
check('fixture 3',solve(*([],)),[])
check('fixture 4',solve(*([127, 129],)),[-1, 1])
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 fixture	Actual	Expected	Outcome
fixture 1	`[-127, 1, 128]`	`[-128, 0, 127]`	Failed
fixture 2	`[1]`	`[0]`	Failed
fixture 3	`[]`	`[]`	Passed
fixture 4	`[0, 2]`	`[-1, 1]`	Failed

SHA-256 / f47006a1c844dc962e03808c51d1c010b8df55974929fa8d10b3bfbe751732cf

HELD IN THE MEMBER ARCHIVE

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

This mechanism has 4 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.

Verification & scope

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 2026-09-29T14:38:42.195984+00:00.

Case digest / 39cea7cb3d200acb942e58501937ec690b950f35b5f3379bffb7e9d0b1b18b0d