Hearth V2: A Deep Dive
Hearth V2 in Purple and Grey

Cortico’s Local Voices Network taps into the intimacy of small conversations to understand and elevate personal stories. To enable in-person conversations, we have developed the digital Hearth, our conversation recording and playback device.

Over the last year, we have refined and improved our original design of the Hearth. These units are almost ready to launch. This post will give you a taste of the Hearth, both inside and out.

Why a Hearth?

A deep conversation can happen anywhere, and often these intimate interactions occur in places where we feel comfortable: in a home, a library, or a quiet corner of a local coffee shop. At Cortico, we aim to meet our conversation participants in the places they are used to, without relying on the infrastructure of a fully wired and sound proofed recording studio. We wanted something that would signal natural connection and not distract with notifications or be associated with other uses (like a smartphone). Seeing nothing that checked all these boxes in existence, we decided to design our own recording device that could be brought into the settings where regular conversations already happen without disrupting the existing cadence and ambience. We arrived at the digital Hearth, a recording device that can function without many requirements (e.g. Wifi, wall power). All that is needed is a (relatively) quiet area and a group of people to sit and share their stories.

The Hearth’s aesthetic and technological design make it an ideal tool to help us record group conversations in a wide variety of places.

Aesthetic Design

The Hearth’s design begins with the simplicity of the circle. A circle has no front or back, and is equally approached from any angle. The Hearth leverages this impartial equity as it sits in the center of a conversation, visually demonstrating that all voices are welcome. From each seat around a table, the Hearth appears the same, both to the conversation facilitator who has led dozens of conversations, and to a new face, joining for the first time.

Subtle changes to this cylindrical shape give purpose and directionality. The fillet on the upper edge cleanly contrasts the chamfer on the bottom. Like a comet or an aerodynamic wing, this shape matches our intuition of motion, and thus presents a natural and stable orientation for the Hearth, while keeping its rotational symmetry.

Wood and fabric have been intertwined with humanity for thousands of years, and can be found in most every home. These materials are tactile and comfortable, evoking both familiarity and symbolic connections. Both feel warm to the touch in a way that plastic and metal often do not.

Hearth V2’s lit interface

As the world fills with various blinks, beeps and buzzes, we designed the Hearth with a careful eye towards delightful user interactions. Throughout a facilitated conversation, the Hearth conveys information about its state, letting the participants know it is ready, recording, or syncing. The device makes use of a subtle lit ring, giving the user just the right amount of information at the moment it is needed. When the the Hearth has no information to offer a user, the lit interface disappears from view, allowing the Hearth to sit passively and unobtrusively in our spaces (note the contrast between lit and unlit in the header image).

Technical Design

Underneath the clean and simple exterior, the Hearth has quite a few interesting technological components.

Hearth V2 contains 8 microphones and an audio speaker

Audio Recording and Playback

Audio is the key emphasis of the Hearth’s internal design, the focus of which is an 8-microphone array. These mics are placed in a 6-inch diameter circle and are each located underneath the fabric speaker grill. The quantity and layout of microphones allows us to add a few key audio post processing features, namely audio direction of arrival (i.e. where someone’s voice is coming from at the beginning of the recording) and beam forming (i.e. the ability to focus on someone’s voice apart from background noise).

The Hearth uses the microphone array to determine from which direction a sound is coming. Human ears are amazing at determining the location of a sound, and we constantly use these sounds to map out the physical world. When someone calls out our name, we can turn to face them without a second thought; for a computer this is not so intuitive. The Hearth accomplishes this task using a combination of several microphones and a bit of sound processing to measure the time delay of a voice between separate microphones.

Knowing voice direction of arrival is useful as we start to listen to the conversation recordings. It is important to figure out who said what in a conversation, a concept called diarization. This allows LVN to both correctly attribute curated personal stories called highlights, and to see how a personal story or opinion develops within a conversation. Conversation participants are seated around the Hearth, and generally remain in the same seat for its duration, so voice direction of arrival can be used as a rough approximation for diarization. However, people inevitably move around, or the Hearth can get bumped, so relying entirely on this directional information is not perfect. By combining the voice direction of arrival information with other information sources we can attain a reasonable level of diarization accuracy.

Our array of 8 microphones lets us improve the audio recording quality using a concept called beam forming. Again, this is a feat that our brains do fantastically. For example, if we are in a noisy room, we can often still hear our conversation partner’s words. Our brains have the ability to focus in on a direction of audio and ignore all other noises. Similarly, once our Hearth knows the direction of the speaker’s voice, it can strategically add and subtract various microphone’s audio in order to focus in on that speaker’s words. (Beam Forming is an awesome concept, and used a large variety of signal acquisition domains).

In addition to sound recording, the Hearth also has the ability to play audio. A high performance full range speaker is contained the in the center of the hearth, just below the fabric. Our speaker and amplifier combination allows us to play back LVN highlights to conversation participants, connecting conversations over space and time — a process we call cross pollination. This ability to share voices from other locations, perspectives, and identities deepens the conversation happening around the Hearth and helps us realize the power of connecting conversations in our network.

The Hearth internals

Hearth Internals

The brain inside of the Hearth is a small computer called a Raspberry Pi (you can see it as the circuit board with the Blue serial number in the photo above). This is an awesome open source computer that can do most everything your laptop can…except it comes in a smaller, more configurable, and more cost effective package. In our Hearths, this allows us to record and playback audio via a connection to the Tablet Controller, as well as communicate with app.LVN.org, our conversation exploration and sensemaking platform.

It is important that the Hearth can be used in a variety of contexts. The design includes a hefty battery system allowing for 10+ hours of continuous conversation recordings. This is a similar system to what you would find in your phone or laptop.

There are several more items that are integral to the Hearth’s functionality; audio speaker and microphone array (see audio section), and lit interfaces and buttons for user interactions.

Hearth v1 and Hearth v2

Improvements from Hearth v1 to Hearth v2

Thanks to our partners and facilitators, we’ve completed hundreds of conversations around Hearth v1. This gave us a complete idea of what we liked and didn’t like in the Hearth. As you can see, the aesthetic design is quite similar between v1 and v2. Facilitators who were familiar with Hearth v1 should feel quite comfortable when they get their hands on version 2.

There are a few key improvements between the two versions. Both the Battery System and the Memory Storage System have been completely revamped. And by focusing Hv2’s design on leveraging modern assembly and manufacturing techniques, we have created a substantially more reliable product.

We have also simplified the design for usability. By reducing the button complexity and moving our lit interface to the top of the device, the Hearth interactions better follow human intuition. And we’ve reduced the Hearth’s size by about one half allowing for much easier portability.

Hearth with Tablet Controller

We are excited to get this new Hearth design into the hands of our facilitators and partners. It is our hope that the thoughtfulness of design and delight of the Hearth serve as visual reminders of the importance of listening, and will help to scale community powered understanding.

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Cortico is a non-profit 501(c)(3) organization led by a multidisciplinary team of experts in community engagement, technology and non-profit management. We strive to meld two elements not typically found in one space: technological innovation and community-centered advocacy. We'd love to keep you up to date on what we're doing!