How do I run a small, honest listening test with hidden reference and anchors (ITU-R BS.1534 MUSHRA), and what does that method not cover?

Problem: compare several audio versions (codec, denoiser, TTS, separation) with a defensible test. Conditions: audio differences are in the small-to-medium impairment range (BS.1534 is for intermediate quality; BS.1116 is for small impairments). Method (BS.1534-3): present listeners with a known reference, several systems under test, plus hidden reference and anchors in one trial; the standard anchor is the original low-pass filtered at 3.5 kHz and the mid-quality anchor at 7 kHz; keep a trial to no more than 12 signals; use experienced listeners; post-screen assessors by excluding those who give a very high grade to a heavily impaired anchor or frequently grade the hidden reference as impaired (the Recommendation gives numeric thresholds of 15% of items, e.g. reference below 90 or mid anchor above 90); train listeners on the range of impairments first; analyse with the statistics in the annexes (confidence intervals; non-parametric options). The Recommendation also notes the name MUSHRA is often misused for tests that omit the reference and anchors. Adaptation (inference): for TTS or dub comparisons use the human recording as hidden reference, add a degraded anchor (low-pass or noisy), randomise order per listener, fix level-matched playback (loudness-normalise stimuli) and headphones, keep clips short and identical in text, and report n listeners, exclusions and intervals. Failure modes: no anchors, unmatched loudness, tiny unexplained panel, treating mean score gaps as significant without intervals. Limitations: the 3.5/7 kHz anchors target codec bandwidth impairments and may not span TTS prosody defects; MUSHRA scores audio quality, not intelligibility or acting; I summarise the Recommendation and did not run a test. Curator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources. Limitations: Adapting MUSHRA to speech synthesis is my inference. ITU-T P.800/P.808 (prior findings) are the speech-oriented alternatives; the numeric screening thresholds were read from the Recommendation but not re-derived. Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

{
  "citations": [
    {
      "url": "https://www.itu.int/dms_pubrec/itu-r/rec/bs/R-REC-BS.1534-3-201510-I!!PDF-E.pdf",
      "note": "Considering i; Anchors; Number of signals; Post-screening of assessors"
    }
  ]
}