Much of the phonetic and phonological research that developed our understanding of the languages sonic qualities owe gratitude to André Classe, Ramón Trujillo and more contemporarily Annie Rialland who, deducted past publications, and conducted herself, spectrographic studies into syllabic translations of Castilian Spanish to Silbo. Her paper Phonological and phonetic aspects of whistled languages* is a rich and highly dense offering explaining in part the developed language’s sonic specifics, amongst other vernacular, giving a deconstruction in such sophisticated detail, thus her work has produced undeniable theorems of Silbo’s sonic properties including deep deciphering of consonant and vowel translative alterations together with methods of articulation. 

“the Silbo system does not simply copy […] movements of speech, but adapts them to respect constraints specific to whistling. […] Rising transitions characterise the coronal phonemes of spoken Spanish, ranging from den- tals to palatals /t d r rr l n s ” j À +/, while falling transitions characterise non-coronal phonemes /p b f m k g x/.”

Here we can peer into some of the complexities of formant languages distinct sonic objects condensed into that of select minute adjustments in pitch, showing Silbo to be migrating  from it’s Spanish formant basis into a tonal language system, limited completely to frequency fundamentals’ linear movement over allotted lengths of time along with modulations in amplitude…

“Two types of whistled consonants were illustrated in Fig. 11: ‘continuous’ consonants, showing an intensity dip, and ‘interrupted’ consonants, showing full interruption.”

She continues to reveal how vowels and consonants differ in modulation of amplitude rationalising that consonants are defined by “dips or silences” in contrast to the “peaks” of vowels. In parallel, frequency changes in consonants have rapid movements where as vowels hold more “quasi-steady” pitch. Furthermore, certain vowels sit strictly within a frequency band and comparatively, the loci of consonants are situated “above and below the vowel range” somewhat like grace notes in musical compositions.