Music of the Deep: An acoustic blueprint of sperm whale codas

Sperm-whale codas are usually described by the number and timing of their clicks. These measures have revealed patterns in whale communication, but leave open how click sound contributes beyond timing and whether the order of whole codas carries additional structure. We investigate these questions through two tiers of acoustic organization, first within codas and then across coda sequences. Frozen pretrained audio encoders provide a framework for measuring acoustic variation beyond timing. We use them to identify recurring forms independently for clicks and whole codas in 1,483 codas, then validate their differences through direct waveform measurements. Within codas, click sound provides information beyond timing alone, while timing remains informative when click composition is held fixed. At the level of complete codas, we also find recurring acoustic forms whose differences are not fully captured by conventional timing-based types. With these forms identified, we examine how ordering contributes at each tier. Within codas, click-form order adds little predictive information beyond composition. Across codas, knowing the last two codas improves prediction over knowing only the last one. Together, these findings support two tiers with different organizing rules: acoustic composition and rhythmic timing within codas, and predictive relationships among whole codas across recorded sequences.

Comparing acoustic structure across very different vocal corpora is difficult because the recordings use different native event units, contain different amounts of sequence, and were collected under different conditions. We develop a matched procedure for comparing such corpora without forcing them into the same event definition. Frozen audio encoders provide a common acoustic representation for recorded events, while matched sampling gives each corpus the same amount of evidence for acoustic and sequence analysis. We apply this procedure to sperm-whale codas, human speech phones, Bengalese-finch syllables, and common-marmoset calls. The comparison reveals different patterns across the four corpora. Sperm-whale recordings stand out broadly: new acoustic forms continue to appear, while their sequences also show strong organization and repetition. Finch recordings show the strongest organization of sounds over time, especially in how neighboring sounds and repeated patterns are arranged. Direct temporal and spectral measurements show that these differences are also present in the recorded sounds themselves. The comparison provides a practical way to measure acoustic diversity and temporal organization across very different vocal corpora by combining a common acoustic representation with matched observation opportunity, without treating their native sounds as equivalent.

Sperm whales (Physeter macrocephalus) communicate through short click sequences called codas, whose structure includes the rhythmic pattern of inter-click intervals (ICI) and the spectral composition of the clicks. In this paper, we propose the Dual-Channel Contrastive Encoder (DCCE), which explicitly encodes rhythm and spectral information with separate encoders before fusing them. We evaluate DCCE on three coda-understanding tasks: social unit, coda type, and individual identification. We compare DCCE against strong baselines from literature under a common linear-probe protocol and analyze the role of each channel and training objective through ablations. On 1,383 codas, shared partitions and validation-only layer selection support three random splits and three recording-date-disjoint folds. DCCE with unit pairing and type supervision achieves mean random-split macro-F1 of 0.901/0.865/0.597 for unit/type/identity. Raw ICI remains strongest for type (0.987), and ICI plus temporal mel statistics is a strong identity reference (0.724). An auxiliary identity objective improves spectral-branch identity prediction but does not improve the mean fused-identity score in this configuration. Date-grouped evaluation and four year holdouts expose generalization limits. The results support task-dependent combinations of timing and spectral information, without establishing independent biological channels or general architectural superiority. Code, notebooks, and complete results are available at https://dcce-research-site.vercel.app.