SLOP3255 · Week 08 · Spectral data
Spectra, colour and redshift#
A spectrum is ordered by wavelength, not by time. Playback creates a timeline that never existed at the telescope.
A spectrum is already a relationship#
The first design obligation is to preserve position along the spectral axis.
From violet to red is not from past to future#
Scanning left to right makes wavelength unfold as playback time. That is useful—but it is a convention, not a physical event sequence.
What does “later” mean in a spectrum sonification?
Hear the continuum and the lines#
Pitch can carry flux while playback time carries wavelength. A marker timbre can distinguish reference lines from measured peaks.
Redshift is a comparison#
redshift = (observed wavelength − rest wavelength) / rest wavelength
Rest reference
A known spectral line at its laboratory wavelength.
Observed line
The corresponding feature shifted in the measured spectrum.
Without the reference, a moved line is only a position—not a redshift claim.
Three ways to render a shifted line#
| Method | Reference cue | Measured cue |
|---|---|---|
| scan time | click at rest position | tone at observed position |
| stereo | centre anchor | left / right offset |
| pitch interval | fixed reference note | mapped comparison note |
The listener needs both positions and the rule that relates their separation to wavelength.
Reference cues need limits#
Known
laboratory line identity
Measured
peak position and width
Inferred
match and redshift estimate
A musical consonance between notes is not evidence that the line identification is correct.
Line width and uncertainty matter#
| Feature | Possible cue | Risk |
|---|---|---|
| peak position | event time | playback resolution |
| line width | tone duration | confused with importance |
| uncertainty | tremolo or boundary tones | decoration can dominate |
The cue should help answer a spectral question, not merely make the sound richer.
Listening Lab 08 · Output: line-identification legend
Find the shifted line#
Task
Compare a synthetic rest spectrum with an observed spectrum and estimate one line shift by listening.
Check
- line identity
- axis direction
- uncertainty range
Reference: NASA/IPAC Extragalactic Database · redshift-independent concepts