STIPA - Speech Intelligibility

Reference-grade measurement accuracy + multichannel audio support This update fixes an issue where a direct signal-path (loopback) test — feeding the built-in STIPA signal straight into the input with no loudspeaker, microphone, room, or noise — reported a stuck reading around 0.30 instead of the near-perfect score expected for an ideal path. Clean measurements now read close to 1.00. What was fixed: - Rebuilt the STIPA test signal to the IEC 60268-16 method using band-limited noise carriers with true intensity modulation (the old signal compressed its own modulation depth). - Rewrote the modulation analysis to measure the intensity envelope at the exact modulation frequencies, with sharper octave-band filtering. New: - Input-channel selection for external multichannel USB / Lightning audio interfaces (Settings → Audio → Input Channel).

- Corrected the modulation frequency table used for STIPA analysis. All seven octave bands (125 Hz – 8 kHz) now use the exact modulation frequencies specified in IEC 60268-16:2011. This was the primary cause of near-zero STI results when using external STIPA sources such as NTI STIPA noise. - Fixed the octave band bandpass filters. A unit mismatch in the filter design formula caused all seven filters to pass the full-spectrum signal instead of isolating their respective octave bands, further degrading measurement accuracy. - Improved the envelope follower response so that modulation frequencies up to 12.5 Hz (required for the 4 kHz and 8 kHz octave bands) are measured accurately. - Fixed a conflict that could disable microphone input when using the built-in test signal generator alongside live measurement.