Dorabella Cipher as Musical Inspiration (2021)

Abstract: The Dorabella cipher is an encrypted note of English composer Edward Elgar, which has defied decipherment attempts for more than a century. While most proposed solutions are English texts, we investigate the hypothe- sis that Dorabella represents enciphered music. We weigh the evidence in favor of and against the hypothesis, devise a simplified music nota- tion, and attempt to reconstruct a melody from the cipher. Our tools are n-gram models of mu- sic which we validate on existing music cor- pora enciphered using monoalphabetic substi- tution. By applying our methods to Dorabella, we produce a decipherment with musical qual- ities, which is then transformed via artful com- position into a listenable melody. Far from ar- guing that the end result represents the only true solution, we instead frame the process of decipherment as part of the composition pro- cess.

## introduction the dorabella cipher (henceforth, simply dorabella) is an encrypted note sent by edward elgar, the composer of the "enigma variations", to his friend dora penny in 1897 @xcite . while many cryptography researchers have assumed that the underlying message is an english text, it has also been hypothesized that it may encode music, since elgar was a composer and a music teacher. this raises several interesting questions. is it possible to find evidence for or against the music hypothesis? what kind of music notation could be devised with only two dozen possible distinct symbols? how would a musical decipherment compare to the proposed textual decipherments? in this paper, we attempt to answer these questions in a principled manner, by using n-gram language models derived from collections of transcribed music. however, we also approach musical decipherment as a creative process. we demonstrate this technique on dorabella, producing a decipherment that has musical qualities, transformed via artful composition into a listenable melody. while prior work typically pursues a single correct decipherment, we instead adopt a creative approach of converting ciphers into music, which might lead to composition of new works. this paper has the following structure: in section 2 we provide background on n-grams, perplexity and monoalphabetic substitution ciphers. in section 3, we discuss prior work. in section 4, we describe our methodology, including datasets for training language models. in section 5, we describe our results on encrypted melody samples. in section 6, our highest-scoring decipherment of dorabella as a melody is used as inspiration to compose a new work. computational decipherment methods are based on heuristic search algorithms guided by statistical n-gram language models @xcite ). an n-gram language model estimates the probability of a token in a sequence based on the previous n-1 tokens. if the token is near the beginning of the string, a special start token is used in place of the missing prior tokens. through repeated applications of this model, the probability of the entire sequence can be estimated. perplexity is a function of probability, which measures the ability of a statistical model to predict a particular sequence. lower perplexity indicates that the model is "less surprised" by the data, and so is said to be a better fit. tokens may be characters or words in natural language, or symbols used in music notation. for compatibility with prior work which models sequences of characters in natural language, we refer to a language model over music notation as a character language model. ## prior work this section describes prior works that use n-gram models for composition, and prior attempts to solve the dorabella cipher. ## methodology in this section, we describe our methodology, including datasets for training language models. ## decipherment results one reason for the lower accuracy on the pitch/duration datasets may be their quality. the original midi files were created by multiple authors, leading to a low consistency in musical transcription. in addition, the files are polyphonic; even for piano music, they often have separate channels for each hand. on the other hand, our melody dataset is monophonic and consistently transcribed. ## composition from decipherment in this section we apply our algorithm to the dorabella cipher, and take the resulting melody as a basis for a composition. in particular, we manually analyze the output for musical content, and modify it according to subjective musical tastes. this creative process is guided by the familiarity with the composer's style, and is not itself replicable. e6 b5 a4 b4 b3 f4 d6 b4 e5 f5 g5 g4 c4 c5 g4 a5 g4 g4 f4 b5 b5 g4 c5 d5 f5 d5 b 4 g5 d4 d6 g4 d6 f4 d5 b4 e5 c6 b4 a4 g4 g4 a4 f4 b 4 c4 d6 g4 g5 g4 f4 e4 d4 c4 c5 d5 e5 e5 d5 g5 d4 a4 d4 f4 e4 d4 a4 c5 e4 a3 b 4 d4 a4 g4 f4 e4 c4 d4 b 4 b4 b5 b 4 d4 f4 b4 c5 d5 figure 3 shows our highest-scoring decipherment of dorabella assuming 4/4 time. figure 4 depicts its musical transcription, which was obtained by applying hillclimbc with a language model derived from the melody dataset (467 samples). this decipherment attempt has some interesting musical features. the notes in figure 4 seem at times to imply logical harmonic progressions. in the second half, there are even moments of motivic repetition, albeit not exact, which evoke a musical composition. figure 5 shows the final version of the output in which some notes (shown in red) have been altered or added in order to create a cadential conclusion. interestingly, our altered 32-bar segment features a highly disjunct first 16-bar phrase, with an altered pitch (b-flat) implying a potential transposition, and a second phrase that is much more lyrical and based on smaller step-wise intervals, complete with the "repeated motive." upon adding the implied harmonic accompaniment, we can see that in some cases there even seem to be an implied v-i cadences, such as between mm. 16-17, mm. 24-25, and the final added measures. adding some phrasing and interesting timbres, as well as chords based on the implied harmony, gives us the audio rendering foot_1 shown in figure 5 . it is important to point out several caveats to this seemingly encouraging result. first and foremost, any analysis of musical composition necessarily has subjective elements. second, we assume that rhythmic values are not encoded in the cipher, and limit the decipherment to quarter-notes. it is also possible that the score may not be connected to common practice notation or even diatonic pitches at all. for example, these could be referring to a very specific set of church bells, or perhaps some other kind of instrument or sonic contraption, or even just rhythm. ## conclusions although we do not claim to have solved the mystery of dorabella, our process produced a listenable melody, which opens up interesting avenues of investigation. in the future, we plan to experiment with different corpora and musical attributes, such as rhythm only. our approach represents a creative way to generate new forms of musical melodies. what seems certain is that elgar's intention to confound left us with a tantalizing riddle that invites further speculation in the future.