Meet our expert Morris Michaels
Aug 24, 2020
7 MIN READ

5 Guiding Principles for Better Voice User Interface Design

The core principles of designing for voice interfaces are the same as those for building visual user interfaces. In both modalities, we need to focus on how the voice assistant will be used, when it will be used, and where our customers will be using it. From there, you need to work around the constraints of the interface and determine the best solution for your unique users and applications. 

While the principles of voice user interface (VUI) design are straightforward, the effort and expertise required is not trivial. There are 5 key considerations UX designers need to keep in mind when building a custom voice user interface:

  1. Plan for usage on a specific device
  2. Choose a voice AI platform
  3. Design for your unique users
  4. Provide user onboarding and training
  5. Use failure as a tool for future success

1. Different devices need different VUI design approaches

Before you begin to design your voice experience, be sure to carefully consider the user. Knowing where and how your users will access the voice assistant will set the foundation for all the other decisions you’ll be making. If the interface is going to be on a mobile phone, the functionality may need to be different than if it’s on a laptop, an IoT device, a TV remote, or a car. So, before you begin the design process, think carefully about the relationship between the user and the voice-enabled device, service, or app.

For example, if you’re designing a voice interface for a car and you want to include navigation, ask yourself questions like:

  • How does the user open the maps with voice?
  • What information do I want to show the user on the screen? 
  • What will the follow-up question or the follow up visuals be?

Those are some of the questions you need to ask as voice product designer. Once you’ve answered these initial questions, the rest of the process is similar to visual design.

The device type affects some key decisions in a VUI design. Just consider the difference between a device that has a screen and one that doesn’t. Obviously, the device that doesn’t have a screen will have a voice-only interface and may include a light or some other indicator that the device is listening. Then, there are devices—like mobile phones or TVs—that have visual screens. 

The user experience with these devices will be very different because they can see information displayed as part of the voice experience. The biggest difference from a design perspective is whether or not you have the ability to show information and display responses. The absence of a screen continues to be one of the biggest challenges for VUI designers.

Knowing where your users will access the voice assistant will set the foundation for all the other decisions you’ll be making. 

Voice interfaces aren’t meant to supplant all other ways of interacting with devices. Multimodal interfaces on devices and products like gaming controllers, IOT devices, mobile phones, and cars most often provide a variety of ways for users to interact, including:

  • Physical buttons
  • Touch screens
  • Voice user interfaces
  • UI elements

Voice is just another way to interact with devices. When you decide to voice-enable your device, you need to decide if the VUI will be the main interface for the device or only be used for specific use cases. Will voice be the primary, secondary or the tertiary input method?  Based on your use cases, once you decide that voice is going to be the primary or secondary method, you need to verify your assumptions through user testing. Use proven testing methods to validate that you’ve identified the right input method for your use case and that you’ve chosen the right priority for voice.

2. Key considerations for choosing a voice AI platform

Every voice platform has a unique set of technological constraints and advantages and it’s imperative that you embrace them all when architecting a voice interaction. When you’re deciding on a voice AI platform, be sure to analyze the following:

  • Connectivity level: Will the device always be connected to the internet or not? If it’s not going to be connected to the internet, the solution needs to be locally embedded on a specific device. 
  • Processing speed: Consider the processing speed of your device and the speed of response required by your users. If the users need speech to be processed in real time, then you’ll need more processing power. And if not, then the query can go to the cloud and the user will need to wait a few seconds. 
  • Accuracy: Different speech models are available on different platforms. Consider any language or terms that your users will use that may not be recognized without customization of the TTS.
  • Multimodality: It’s very important to take into account which other modes of interaction your users will have available for your product, device, or app. 
  • Environmental testing: It’s vital to know how much and what kind of environmental testing has been performed on the voice engine. Has it been tested in multiple environments, at different times of day? How about in windy or noisy conditions, while walking outside or indoors with ambient noise? All of those factors have an effect on the effectiveness of the voice solution itself. 

3. Design your VUI with the user in mind

As a designer—and as a problem solver—it’s very important to remember that we’re ultimately designing a solution for our users. I think the most important element of VUI design is to always think about our users’ pain points and the problems that we’re trying to solve for them.

Test frequently to make sure your users find your voice interface useful and delightful. Test, test, iterate, and test some more. It’s more challenging to test user interaction with voice than with visual design. When you’re designing for a visual interface, you can take the user from A to B by pressing a button. With voice, we actually need to build a prototype and see how the user interacts with it. Observing without influencing user behaviors can be challenging.

To understand your users’ experiences, you can conduct surveys or put the voice UI in front of a few people to see how they interact. However, the best method is to locate potential users or existing users of your solution and talk to them, listen to them, and get the voice solution in front of them to see how they’d actually use it, and observe their emotional responses.

I think the most important element of VUI design is to always think about our users’ pain points and the problems that we’re trying to solve for them.

So much of the success of a voice user interface is psychological and subjective. To really understand the user experience, you need actual users to tell you how they feel when they are interacting with your voice assistant. Most of the time, it’s going to be different than what you feel or what other people in our team might feel. So, it’s important to get as much feedback from actual users on almost everything that you are doing to confirm the viability of your design decisions.

4. The importance of user onboarding and ongoing education

 As difficult as it was for people to adopt typing, tapping, and swiping on phones and tablets less than a decade ago, those actions are now habitual and changing them actually requires some education and onboarding. 

User education helps to reinforce how best to use a VUI and lets users find ways to enhance their experience for a specific domain or use case. First of all, the VUI needs to add real value to get people to use it frequently. We see that in use cases like weather forecasts, alarm clocks, and recipes, voice interfaces are working really well. People have discovered the convenience of hands-free interfaces for these types of use cases and they’re repeating their behavior and coming back again and again. 

In other use cases, voice adoption has been a little slower and a bit more challenging. In those cases, the voice interface can be improved as well as the domain itself. The key is to focus your fixes on the voice experience of specific domains where the user experience isn’t as seamless as it should be. 

Creating a voice-first experience in a domain that users frequently access often hinges on the quality of the user education—prompting them to try more queries or letting them know what they can do that they haven’t yet tried. When user education accompanies the introduction of a new domain, we see an increase in usage. For example, if a user uses your assistant to check what time their flight leaves, it may be helpful for them to know that they can also use the same assistant to book an Uber ride to the airport. This type of ongoing user education should be an integral part of your plan.

When I started my career, UX was only for the web. Users interacted with one screen and it was relatively easy. And when screen sizes changed, it was still just web design. When mobile devices started getting popular in 2007, things started to change. All of a sudden, people were using their fingers instead of a mouse and keyboard. 

The challenge with mobile was that the small screens afforded a smaller available space for design elements and the whole paradigm changed. The way we were thinking about the user changed because the user was no longer only at a desk or at home, the user was everywhere—not only in an office or a room. Now, we are seeing another paradigm shift where the user doesn’t not necessarily even need a screen and access is immediate and hands-free. As VUI designers, we need to keep this in mind at every stage of design and then test and iterate, test and iterate, and then test some more to deliver user experiences that are satisfying and delightful.

Creating a voice-first experience in a domain that users frequently access often hinges on the quality of the user education—prompting them to try more queries or letting them know what they can do that they haven’t yet tried.

5. Documentation and learning from voice AI failures

One of the most important things to do as a product designer is to document everything that you’re doing. Document your successes as well as your failures and slowly build a framework for a voice UI design. The documentation that you create in this iteration will be the foundation and framework that your colleagues will use for the next voice project. 

Be sure to document all the best practices and learnings over the course of designing your VUI. Even though the next team or the next project may be designing for a different device, or a different environment, the same best practices and solutions that were successful for your solution will help inform any new endeavors.

Document your successes as well as your failures and slowly build a framework for better voice UI design.

Document everything. When you try and fail, that is some of the most important information to share as it may help future teams from trying and failing just as you did. You must expect to fail, but it’s better for your organization if you set up the next team or the next project for greater success. 

If you’re looking for some more VUI design recommendations, our in-depth Best Practice Guide: Building a Better Voice User Interface has actionable tips and advice from 15+ experts to help you at any stage of design. 

Explore Houndify’s independent voice AI platform and register for a free account at Houndify.com, or talk to us about how we can help you bring your voice strategy to life.

Morris Michael, Author

Morris Michael is a product design lead at SoundHound Inc. with 20 years of experience. In his free time he likes to create card and board games.

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