If you listen to old radio dramas, you may notice that women's voices are often pitched higher than you may be used to. It may be because, as researchers have found, women in English-speaking countries are actually speaking with deeper voices. A BBC report from 2018 explained:
The researchers compared archival recordings of women talking in 1945 with more recent recordings taken in the early 1990s. The team found that the “fundamental frequency” had dropped by 23 Hz over five decades – from an average of 229 Hz (roughly an A# below middle C) to 206 Hz (roughly a G#). That’s a significant, audible difference.
The researchers tried to control for external variables that may result in vocal changes:
The researchers had carefully selected their samples to control for any potential demographic factors: the women were all university students and none of them smoked. The team also considered the fact that members of the more recent group from the 1990s were using the contraceptive pill, which could have led to hormonal changes that could have altered the vocal chords. Yet the drop in pitch remained even when the team excluded those women from their sample.
Their best guess is that women have habitually deepened their voices as they have gained authority in society:
Instead, the researchers speculated that the transformation reflects the rise of women to more prominent roles in society, leading them to adopt a deeper tone to project authority and dominance in the workplace.