In this blog post, we explore why phone call voices sound different from actual voices and the technical principles behind it.
When dealing with criminals in movies, one particularly striking element is the perpetrator’s voice. As the screen darkens and a character, holding their breath, answers the phone, the criminal’s eerie voice instantly heightens tension to its peak. Similarly, the phone voice featured in many films plays a crucial role in instilling fear in the audience. Scenes where the voice of a kidnapper, having abducted a child, comes through the phone line are particularly threatening, relying solely on that voice. Many might think this voice heard in films is merely a directorial technique, but the reason the phone voice sounds different from the original voice stems from actual technical causes.
In reality, too, the voice heard during a phone call differs from the voice when speaking face-to-face. This is due to modulation occurring during the process where the telephone converts the voice into an electrical signal for transmission. The original voice undergoes various changes in sound quality, timbre, and frequency range simply through this mechanical process. Consequently, investigative agencies face limitations in identifying suspects based solely on a phone voice. Films often deliberately distort phone voices to create a terrifying atmosphere.
So, let’s examine how telephones operate and how voice modulation occurs. The fundamental principle of a telephone is converting speech into electrical signals and transmitting them to the recipient. This process involves two main stages. The first is the microphone converting sound into electrical signals. The second is transmitting that signal, which the receiver then reproduces as sound through a speaker. The voice frequency transmitted as a telephone signal is limited to approximately 300Hz to 3,400Hz. The full range of human voice frequencies spans roughly 20Hz to 20,000Hz, meaning only a portion of this spectrum is conveyed by the telephone. Consequently, much of the low and high-frequency components of a person’s voice are lost.
This frequency band limitation is a key reason why a criminal’s voice sounds different. Voice recordings in movies or real-life phone calls, constrained by this limited frequency range, sound flatter, with diminished timbre, and emphasize higher pitches. In reality, voices over the phone also feel sharper and more unfamiliar than the original. Crime films often exploit this to make the criminal’s voice sound even more bizarrely distorted.
Furthermore, when voice modulation technology is used in crime films, specific sound effects are often added to amplify the sense of dread. These sound effects serve as dramatic elements, particularly in scenes depicting kidnapping or threatening phone calls. Typically, both high and low frequencies are simultaneously emphasized, or irregular electronic sound effects are added, making the psychological tension of the person receiving the call feel more vividly real to the viewer. Adding tremors or echo effects to voices is another frequently used technique for creating a frightening atmosphere.
Such voice modulation doesn’t merely function as a cinematic technique; it also plays a crucial role in actual criminal investigations. Investigative agencies attempt to identify suspects through voice modulation and voice analysis in cases involving threats made over the phone or the appearance of unidentified individuals. Techniques like analyzing specific frequencies to identify unique vocal characteristics or examining timbre to match a voice to a specific individual fall under this category. Recently, advancements in voice analysis technology using artificial intelligence (AI) have enabled the analysis of even the most subtle vocal traits that were previously indistinguishable.
Thus, voice modulation and sound effects in phone calls carry significant real-world implications beyond mere gimmicks. Films, in particular, dramatically leverage this to heighten audience tension solely through the criminal’s voice. The fact that voices alone can induce psychological pressure underscores how crucial vocal differences are in phone-based criminal investigations.
