Five views.
One signal.

1. 01SpectrumLow / high tone375 Hz and 6 kHz sine tones alternate every 1.5 seconds.Energy moves across the ERB field; centroid and rolloff follow it.00:06OPEN SIGNAL →
2. 02Pitch classSame class, one octave apartA3 at 220 Hz and A4 at 440 Hz alternate every 1.5 seconds.The strongest pitch class stays near A while the waveform period changes.00:06OPEN SIGNAL →
3. 03WaveformThree wave shapesA 220 Hz sine, triangle and softly clipped sine play for two seconds each.The trace and crest factor change even though frequency and peak stay fixed.00:06OPEN SIGNAL →
4. 04PeriodicityPeriodic pulse trainFifteen short dual-tone transients recur every 0.5 seconds.After enough history, a candidate settles near 120 BPM-equivalent.00:08OPEN SIGNAL →
5. 05SimilarityA–B–A–C sequenceFour two-second spectral shapes follow A–B–A–C; the second A is quieter.An off-diagonal match appears when A returns despite its lower level.00:08OPEN SIGNAL →

The methods are literature-backed and internally tested. The examples demonstrate implementation behavior; they are not peer review, perceptual proof or calibrated measurement.