Audio forensics behind the Iron Curtain: from raw sounds to expert testimony

ABSTRACT

This essay investigates the construction of forensic audio expertise in the legal and security system of Communist Czechoslovakia and shows that the contested nature of speaker identification and sound-based objectivity contributed to the formulation of probabilistic claims in forensics. It explores the practices of the Department of Fonoscopy: a unique research laboratory of audio forensics that systematically examined the spectrographic, linguistic, and auditory means of sound analysis for the purpose of identifying unknown voices and environments in audio recordings. Bringing together the notions of “forensic cultures” and “sonic skills”, this article addresses the scientific, cultural, and political underpinning of the nascent field of audio expertise as well as the changing status of sound-based knowledge and forms of representation in forensics. In establishing fonoscopic expertise before the court and in the broader praxis of police investigation, the idea of vocal fingerprints and the use of sound visualisation technologies became instrumental. This essay pays special attention to the dynamics of the intricate process in which acoustic “raw material” (from anonymous calls, wiretapped phone lines, recorded conversations, or police interrogation rooms) was transformed into different kinds of legal and criminalistic evidence in the service of the totalitarian surveillance state.

KEYWORDS:

• Speaker identification
• fonoscopy
• audio forensics
• voiceprint
• sonic skills
• expert testimony
• acoustic evidence
• probability scale

Acknowledgments

The writing of this article was funded by the Czech Science Foundation under the research project The Second Sense: Sound, Hearing and Nature in Czech Modernity (20-30516). The first version was written for the workshop Forensic Voices: Cultures of Identification Through Sound held at Maastricht University in June 2022. The author would like to thank Václava Musilová and Jan Málek for sharing details about their professional work at the Institute of Criminalistics, Radek Skarnitzl for his insights about the recent development in audio forensics, and the anonymous reviewers for their comments.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notes

1. https://www.novinky.cz/krimi/clanek/p olicie-bude-hlucha-opousti-ji-jediny-expert-na-analyzu-hlasu −62,843); https://www.irozhlas.cz/zpravy-domov/policii-od-noveho-roku-opousti-jediny-expert-na-analyzu-hlasu_201010111632_kbrezovska;https://www.idnes.cz/zpravy/cerna-kronika/policii-chybeji-pismoznalci-odchazi-i-jediny-expert-na-rozbor-hlasu.A101011_114708_krimi_js (accessed September 16, 2022). All translations from Czech are mine. I am grateful to Jan Málek for sharing details about his work at the Institute of Criminalistics in the interviews held on July 25 and September 6, 2019.

2. The department was established under the authority of Public Security (Veřejná bezpečnost) by the Ministry of the Interior, Resolution ČSSR No. 35/73 (1975). Criminalistics is the application of scientific methods to the investigation of crime; its results are applied to matters of criminal and civil law. The expressions criminalistics and forensics and treated as synonymous in this article.

3. I have translated the Czech word fonoskopie as “fonoscopy” in English to refer to a specific method and tradition of forensic acoustics that emerged in Czechoslovakia in the 1970s and Poland in the 1960s. The English term “phonoscopy”, in contrast, has a narrow medical meaning and refers to sound analysis made by the phonoscope.

4. See, for example, Theen (1980). A different approach is represented by Iacob et al. (2018). The notion of “expertise” I adopt in this paper de-emphasises the expert’s direct intervention in public affairs.

5. In the 1960s, the Czech phonetician Přemysl Janota conducted original, internationally acknowledged research on speech’s personal characteristics by investigating the speech spectrum and artificial speech. For Janota’s listening experiments at Charles University and the exact nature of knowledge transfer between phonetics, aviation, and fonoscopy, see Kvicalova (2023).

6. See the essay by Michael Mopas in this issue. These issues are also discussed in the “witness seminar” on speaker identification (Bijsterveld and Kvicalova 2023).

7. See Kvicalova (2023, 388–9). Despite the initiation of fonoscopy in Poland in the early 1960s, its institutional development has yet to be researched. See Maciejko, Rzeszotarski, and Tomaszewski (2010); and Málek and Musilová (1989, 7). The term fonoscopy was first used in Polish forensics by Andrzej Szwarc in 1964 (Szwarc 1964).

8. Christian Koristka was in charge of audio forensics at the Department of Criminalistics established at Humboldt University in 1968 (Bijsterveld 2021).

9. Czechoslovak fonoscopy never assumed a standardised form to be applied to every fonoscopic analysis. See Kvicalova (2023).

10. A27 (1981), 268, ABSCR. Compare to the project of “The Voice Operated Typewriter” (Li and Mills 2019, 143). See also Karin Bijsterveld’s article in this issue.

11. Compare to Bijsterveld (2021).

12. For the regulations concerning short and long-term eavesdropping see Povolný 2001 as well as TA-111, TA-122, TA-133, “Situace ve využívání operativní techniky”, and “Návrh prognózy zpravodajské činnosti”. Many of those listening to the permanently wiretapped lines were women. See A27, Books of permanent service 1975–1989, ABSCR.

13. The potential of directional parabolic microphones used in the field recordings of bird songs was explored in this respect, but a similar device that could record human voice over a long enough distance without being detected was never constructed. A27/191 (1975), 22. ABSCR. A microphone capable of performing the desired function would have to be very large, thus undermining the operation’s secrecy. Despite the Czechoslovak state’s best efforts to invent original eavesdropping devices based on novel technological principles that would be difficult for foreign enemies to detect, many of the recording and monitoring devices were purchased abroad in capitalist countries, primarily West Germany (many electroacoustic devices were purchased from PK Elektronic in Hamburg) but also Denmark and the US. See ZSGŠ, BF-S53, 1979, 9, See also II. Správa FMV [“Situace ve využívání operativní techniky a některé náměty na její zefektivnění”], (May 5, 1975), ABSCR.

14. Resolution MV 1960/194–10/12–47–III/2 of the Ministry of the Interior (December 10, 1947). See also Hlaváček (2007–2010).

15. Resolution of the Ministry of the Interior No.166 (December 12.,1958), appendix č. 1, čl. 11, ABSCR.

16. See the administrative book of the Department of Fonoscopy (henceforth ABD), AFD.

17. As was the case in W. Doegen’s project in the Berlin Lautarchiv in the 1920s. See Li and Mills (2019, S130)

18. The relationship between sound and the construction of race has been described in connection to the supposed vocal and aural markers of Black identity in the United States. See Stoever (2016) and Eidsheim (2019).

19. See ABD, July 26, 1979 (I MV ČSSR), March 7, 1980 (XI/s FMV & SL I), helicopter crash; August 14, 1981, dangerous landing; plane crash L-39 OK 184, Kbely; October 21, 1981, plane crash HA-LCF, AFD.

20. A serial killer, Jiří Straka, attacked eleven women in Prague in 1985, killing three of them. The case received significant attention in the media as the attacks spanned almost seven month and took place when Prague was hosting the Spartakiad, a mass gymnastics event, which took place every five years beginning in 1955.

21. For example, the request to copy the sound files from the wiretapped landline of the famous dissident Alexandr Vondra (August 8, 1989), ABD.

22. Some of the cases were Říha (1978, requested by defence lawyers); Machart (1982); Šiff (1984, anonymous calls), ABD.

23. The notion of sonic skills expands on Jonathan Sterne’s term audile technique, which describes listening as a distinctively modern technical skill (Bijsterveld 2019; Sterne 2003).

24. The film was produced for the Ministry of the Interior’s internal use by Krátký film Praha (Prague Short Films) at the film labs in Barrandov. Most copies of the 16 mm film were destroyed or lost; the only copy I managed to retrieve, thanks to the assistance of Zdeněk Kopecký, is archived at the Prague Police Museum.

25. Compare to Li and Mills, who describe airline bomb threats as being one of the reasons why the FBI turned to the Bell Labs for a technical solution in the 1960s (Li and Mills 2019, S139).

26. Voiceprint Laboratories, Inc., Somerville, N.J. The exact story of how the instrument reached Communist Czechoslovakia remains unknown.

27. Sound spectrograms are visual representations of sound frequency and intensity as it unfolds in time, which is close to how sound is perceived by the human ear. Although the words sonogram and spectrogram were often used interchangeably, the former was preferred in the Czechoslovak context.

28. The use of miniatures in courtrooms during the first half of the twentieth century is discussed by Neale (2020).

29. This is not necessarily the case today, when an increasing number of sound recordings are made by mobile phones. Compare to the interview with Peter French, Comparing Voices.

30. See the essay by Josephine Hoegaerts in this special issue. See also Li and Mills (2019).

31. The first sound spectrographs were used at Bell Telephone Laboratories as early as the 1940s. For this history – the research program and its later military applications – see Mills (2010); Li and Mills (2019); and Potter, Kopp, and Green (1947).

32. This tradition goes back to Erns Chladni’s Klangfiguren – spatial figurations of sound frequencies as they appear in thin layers of sand on glass or metal plates (Zielinski 2006, fn 16, 159–204), and Erlmann (2010, 155–56, 189–94).

33. Kersta founded his own company, Voiceprint Laboratories, becoming a renowned expert in voice identification in the US. For more information about the nature of his collaboration with police forces and legal authorities, see Zbikowski (2002).

34. The critical reflection of the idea of voiceprint in Czechoslovak fonoscopy is thoroughly discussed in Kvicalova (2023).

35. The epistemic roles of sound and hearing have been studied in various experimental, academic, cultural, and technological contexts; see Sterne (2003), Bruyninckx (2018), Hui, Kursell, and Jackson (2013), Birdsall and Tkaczyk (2019), Tkaczyk (2023), Mody (2005), Rice (2012), Thompson (2002), and Bijsterveld (2019).

36. Daston and Galison (2007).

37. “Such phonetic characteristics can usually be measured by instruments, which implies a completely objective assessment of these phenomena” (Musilová 1977, 369).

38. See Mopas (2023), in this issue.

39. Málek was a graduate of CTU, Faculty of Electrical Engineering, where he majored in audio. He also took classes in phonetics at the Faculty of Arts with the well-known phoneticians Přemysl Janota and Milan Romportl (Kvicalova 2023).

40. See Bruno Latour’s notion of “immutable mobiles” (Latour and Woolgar 1986).

41. The view that the photograph represented the human body better than its written description accompanied already its first forensic uses in the second half of the nineteenth century (Cole 2002, 20).

42. Although Goodwin begins his article with the 1992 Rodney King case, where forensic sound analysis played a key role, he does not consider professional listening as a viable category and instead concentrates on visual aspects of expertise. For the use of audio forensic expertise in this case, see Angelika Braun’s recollection, Comparing Voices.

43. The notion of the “professional audition” in the context of audio engineering was proposed by Thomas Porcello (2004). The professional audition in aural field observations is discussed in Bruyninckx (2018, 536).

44. Recorded confessions were instrumental in Stalin’s show trials (1948–1953), when they were played back in courtrooms for performative and emotional, rather than forensic, motives (Vorel, Šimánková, and Babka 2003, 224–34).

45. See the interview with Peter French, Comparing Voices.

46. Compare to the 1969 conclusions of the Technical Committee on Speech Communication of the Acoustic Society of America, which explicitly stated that spectrograms could have misled the jury (Bolt et al. 1969, 600, 602).

47. Compare to the present-day audio forensic evaluations before the court, in which “objectivity” is often explicitly evoked by the expert. See the discussion in the final part of this essay.

48. Interview with Václava Musilová, June 9, 2020. The appearances of fonoscopy experts before different courts are recorded in ABD.

49. This seems to have been a more general trend in forensic audio analysis towards the end of the 1980s (Bijsterveld 2021; French 2017).

50. The current use of automated and semi-automated fingerprint identification system is further discussed in Dror and Mnookin (2010).

51. See the police announcement: https://adoc.pub/policista-roku-2008-str-.html (accessed October 15, 2022).

52. This contrasts with the situation in the GDR, where most experts involved in voice identification before the fall of the Berlin Wall in 1989 did not pass the so-called Gauck examinations and left the police in the 1990s. See the discussion with Angelika Braun, Comparing Voices.

53. https://www.e15.cz/clanek/magazin/umi-naslouchat-a-odhalit-vyderace-849132 (accessed September 2, 2022).

54. An interest in new methods of automatic speech recognition was among the reasons for Málek’s first trip to Berlin in 1980. See Málek’s field notes, AFD.

55. The combination of aural, mechanic and, in certain cases, automatic analysis is recommended by most members of the International Association for Forensic Phonetics and Acoustics (IAFPA). See French (2017) and Gold and French (2019); see also the essay by Michael Mopas in this special issue.

56. For the discussion see Kvicalova and Bijsterveld (2023).

57. Only one of the three expert witnesses, Marie Hes Svobodová, is based at the Institute of Criminalistics. Radek Skarnitzl, the head of the Institute of Phonetics at Charles University, is a leading member of the IAFPA, active in drafting new standards for forensic expert witnessing as a member of the Ministry of Justice’s advisory board. See Skarnitzl (2022), and his illustrative report at https://znalci.justice.cz/dokumenty/#dokumenty. The third expert is Zdeněk Švenda, whose work is based solely on automatic recognition (“Svendaz Atomatic Speaker Recognition”).

58. http://svendaz.cz/html/hlas.html.

59. In the UK, for example, expert testimony based solely on automatic speaker recognition is not admissible. In Germany, it is rare for more than one audio forensic expert to be asked to submit a review. See Kvicalova and Bijsterveld (2023).

60. County Court Verdict from November 26, 2013, Brno/Zlín (No. 61T 7/2013–5030).

61. Ibid, 60–63.

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Notes on contributors

Anna Kvicalova

Anna Kvicalova is a historian of science, religion, and the senses. In her work, she deals with the history of sound-based knowledge and listening skills. She is a permanent research fellow at the Centre for Theoretical Study (Charles University and the Czech Academy of Sciences), where she is the leader of the research project The Second Sense: Sound, Hearing and Nature in Czech Modernity. She received an MA from the University of Amsterdam and a PhD from Freie Universität Berlin. Between 2013 and 2017, she was a research fellow at the Max Planck Institute for the History of Science in Berlin. She is the author of Listening and Knowledge in Reformation Europe (Palgrave, 2019) and other publications on sound, hearing, and acoustics (published with Annals of Science; Sixteenth-Century Journal; or Technology and Culture). She is also an assistant professor in the Department for the Study of Religions at Masaryk University, Brno