There are a few key reasons why female voices are often perceived as sounding better than male voices, especially for virtual assistants, navigation systems, and other voice interfaces.
Higher Pitch
One of the main factors is that women’s voices are typically higher-pitched than men’s. The average female voice has a pitch around 180-255 Hz, while the typical male voice is around 85-155 Hz. Higher pitches tend to convey certain positive attributes such as warmth, politeness, and unobtrusiveness. Lower pitches can sometimes sound more authoritative, but higher pitches avoid sounding as imposing or dominant.
As most virtual assistants are designed to have an affable and approachable personality, the slightly higher pitch of a female voice fits these goals more closely. The higher pitch is less jarring coming from a disembodied AI assistant. Additionally, higher frequencies are easier for many people to hear clearly, an important factor for voice interfaces.
Variations in Vocal Tract Shape
In addition to pitch, differences in the vocal tract between males and females also affect voice quality. Women generally have a shorter vocal tract which emphasizes formant frequencies – the resonant frequencies of the vocal tract – in a way that makes the voice sound subjectively more pleasant.
Related to this is vowel space size, which is larger in female speakers. The richer vowel sounds are another factor contributing to the pleasing quality of women’s voices compared to men’s.
Less Vocal Fry and Creakiness
While some male voices can sound very smooth, others exhibit more vocal fry, creakiness, and irregular vibration of the vocal folds. These rougher qualities are much less common in female voices, which tend to sound overall smoother and clearer as a result.
The virtual assistant companies carefully select and modify voice samples to avoid any vocal fry or excessive creakiness, contributing to the cleaner female voice most people are familiar with.
More Breathiness Allowed
A moderate amount of breathiness in a voice reinforces the impression of a smoother, warmer, and more intimate vocal quality. While too much breathiness could sound whispery or weak, just a touch can sound pleasant and even convey a sense of vulnerability that makes a voice more relatable.
Slightly more breathy voices are more common and socially accepted among females, making this vocal quality easier to include at moderate levels.
Hormones and Vocal Fold Mass
In addition to differences in vocal tract size, females also tend to have thinner and lighter vocal folds compared to males. This mass difference affects tissue pliability and vibration mode, influencing voice quality. The thinner folds help create a softer, breathier sound at times.
Hormone levels are one factor influencing vocal fold tissue properties, and may partly explain why some pre-adolescent boys and transgender women undergoing hormone therapy can sound similar to cisgender adult females in terms of voice quality.
Speech Patterns and Emotional Expression
Women are, on average, more expressive in speech, using more variations in pitch, pronunciation, and word choice to convey emotion. This allows inserting more warmth, enthusiasm, sympathy, or other emotions that can positively influence perceptions of the voice.
Speech patterns also differ, with women exhibiting more cooperative conversational styles of interacting. The vocal assistant personas leverage these female speech style patterns – for instance, being agreeable, using tag questions, apologizing more, etc. – to shape the user experience.
User Expectations and Assumptions
Listeners also filter voices through their social and cultural assumptions. Because of the extensive history associating female voices with assistant roles – secretaries, service industry workers, home assistants, etc. – users may unconsciously expect that pattern and respond more positively when it matches.
Relatedly, there are stereotypical assumptions about male and female speech patterns and emotional expression. Users’ expectations derived from gender stereotypes likely reinforce perceptions of female voices as sounding better for virtual assistants playing a helpful, supportive role.
Early Virtual Assistant Voices Were Female
Part of users’ expectations come from early precedents – many of the first successful virtual assistants like Siri used female voices. This set the tone for users to expect and desire that type of voice.
People tend to prefer things that sound familiar. The now extensive history of female-voiced assistants like Siri and Alexa trains users to respond better to that type of voice, even if they might not otherwise inherently prefer it.
Preference for Female Voices in Other Roles
Research has found that people tend to prefer female voices over male voices for a variety of automated roles, beyond just virtual assistants:
- Automated telephone operators
- GPS navigation system voices
- Public transit announcers
- Automated airport announcers
So there seems to be something universally appealing about female voices in human-computer interaction systems. The preference applies broadly, likely for many of the reasons discussed above.
Individual Differences in Voice Appeal
While many people do perceive female voices as better overall for virtual assistant roles, there are also significant individual differences. Personal taste, gender, age, culture, accent, and many other factors influence perceived voice appeal.
Some key considerations around individual differences include:
- Men show less strong preference for female voices than women do.
- Younger adults have an even stronger female voice preference than older people.
- Regional accents can significantly impact appeal – certain accents are perceived much more positively.
- Voice pitch, cadence, clarity and other parameters still matter, regardless of gender.
- Balancing gender stereotypes versus breaking stereotypes also affects perceptions.
While the generalized preference for female voices is clear, individual differences mean some will still perceive male voices as better for certain contexts. Voice appeal is subjective and depends on the specific voice, the role, and the listener.
Recent Research Findings
Here is a summary of key findings from some recent research studies investigating virtual assistant voice gender preferences:
| Study | Key Findings |
|---|---|
| Nass & Brave 2005 | Participants rated female-voiced computers as more helpful, pleasant, and polite. Male voices were found more credible. |
| Qutee 2014 | Younger people were most favorable toward female voices. All groups found the female voice more welcoming. |
| Pickerill 2019 | 31% preferred female voices, only 12% preferred male. Higher pitches were seen as most suitable. |
| Clifford 2019 | Female voices were rated as more warm, happy, and sympathetic. Male voices scored higher on competence. |
While there are some nuances around perceived competence and authoritativeness, most studies confirm the significant preference for female virtual assistant voices.
Voice Design Implications
The research has clear implications for crafting pleasant and effective virtual assistant voices:
- Higher pitch female voices tend to be the safest, most universally appealing option.
- Vocal quality matters – smoothness and moderate expressiveness is important.
- Certain regional accents tend to be preferred by users.
- Personalization allowing voice gender choice allows catering to individual differences.
- Testing with the target user population is important when selecting voice samples.
- Certain applications may call for male voices or gender-neutral voices.
Carefully evaluating the assistant persona, user population, and application context guides voice gender selection and optimization decisions to provide the best user experience.
The Future of Virtual Assistant Voices
It’s likely that female voices will continue to dominate most virtual assistant roles in the near future. However, expectations may evolve over time:
- Greater demand for inclusive options catered to diversity.
- User comfort with artificial voices distinct from either gender.
- Voices customized for individual apps and devices.
- More options for personalized voices tied to individual preferences.
- More dynamic voice patterns and emotional expression.
While female voices currently sound better overall, the landscape of virtual assistant voices will likely continue expanding and evolving to sound even more natural, unique, and personalized in the years ahead.
Conclusion
Female voices tend to be perceived as more pleasant, approachable, and cooperative, making them a natural fit for virtual assistant roles. Factors like pitch, vocal tract shape, smoothness, and breathiness contribute to these positive perceptions. Social conditioning also leads users to expect a female assistant voice. However, there are still individual differences, and future advances may lead to more inclusive and personalized voice options.