Sound & hearing
Before a note has a name, sound is changing pressure through time. A source moves, air carries that motion, the ear converts it, and the brain groups the evidence into pitch, loudness, timbre and separate auditory objects.
One signal, several questions
x(t) = A(t) · sin(2πft + φ)f controls repetition rate, A(t) shapes level through time, and φ locates the cycle. Real instruments sum many changing components.| View | Question | Do not confuse it with |
|---|---|---|
| Waveform | How does pressure/amplitude change through time? | A complete explanation of pitch or timbre |
| Spectrum | Which frequencies are present now? | A performance history |
| Spectrogram | How does spectral energy change over time? | A musical score |
| Envelope | How does one sound begin, continue and end? | Note duration alone |
A note is also a shape in time
note-on → attack → sustain → releaseduration ≠ gate ≠ releaseDuration reserves musical time. Gate schedules note-off inside it. The instrument envelope determines how long the release tail remains audible.Measurement is not perception
A digital meter can report RMS level and dBFS. Hearing also depends on frequency, duration, masking, recent context and playback level. Therefore dBFS is not perceived loudness, and spectral centroid is only one correlate of brightness.
A strong sound can make a nearby frequency or nearby moment harder to hear. Adding a layer can reduce clarity even when every track is audible alone.
Use “brighter than the previous state” or “lower measured level”, with method and confidence. Do not turn one metric into an emotion label.
Reading the evidence panel
| Evidence | Mechanism | Useful comparison |
|---|---|---|
| Level | 20 log₁₀(RMS) from PCM | Did the rendered signal become stronger or weaker? |
| Brightness | Energy-weighted FFT frequency, or spectral centroid | Did spectral weight move upward or downward? |
| Roughness | Interaction of strong nearby spectral peaks | Did partials crowd the same critical region? |
| Harmonicity | How strongly the PCM waveform repeats | Did the sound become more or less periodic? |
| Transient | Frame-to-frame level rise plus high-frequency onset energy | Was this onset sharper than the previous frame? |
| Masking | Overlap between separately captured voice spectra | Are simultaneous voices competing for the same bands? |
| Width | Side energy compared with total mid/side energy | Did the rendered stereo field become wider? |
measurement + context ≠ emotion“Higher measured roughness than before” is evidence. “This sound is angry” is an unsupported cultural and psychological claim.- Hold one note with Rich oscillator, then choose Stereo Grand.
- Compare waveform, spectrum and envelope/release behavior.
- Keep the pitch fixed: any visual change now comes from source and performance, not note name.
Terms, relations and sources
Key terms
soundenvelopespectrummaskingRelated chapters
Layers & texturePsychoacoustic sourcesDetailed lookup
Notation legendEvidence
Editorial sourcesModels state their boundary; tradition-specific claims require specialist sources.