As medical devices grow in complexity, developers gain opportunities to move beyond compliance and create exceptional user experiences. While FDA guidelines specify the design and application of alerts and alarms, there is ample room to leverage the powerful ability of sound to communicate information directly to the user. Medical developers can focus more on the product sound design process, as it brings intention, emotion, and meaning into the experience of devices. By aligning the process of product sound design with medical guidelines for alerts and alarms, medical devices gain a new opportunity to connect more deeply with their users.
Earcons: Communicating Ideas and Meaning through Sound
From washing machines to cardiac monitors, products can be noisy. To simplify the problem, product sound designers categorize product sounds into two main types: consequential sounds and intentional sounds. Consequential sounds are the inherent, resulting sounds from a product’s functionality, like the sound of a car door closing or a fan’s motor humming. Intentional sounds are the added sounds that reinforce the functionality, or experience of a product, like the boot-up sound of your laptop, or the alarm on an ambulance truck.1
Earcons are one type of intentional sound added to a product to use simple, abstract musical passages to help communicate potentially complex information. Think of the earcon following a button press on an electronic device: sound provides the assurance and confidence that the input was properly received. But this audible feedback can also communicate something more. Is the tone rapid and high-pitched to convey urgency in confirming the selection? Or is the tone gradual and melodic, to instill a sense of personality and ambience into the experience? To create earcons that highlight the desired experience of a product, sound designers consider a variety of inputs, including the purpose of the sound, the user and use case, and the desired emotional response.
The spectrum of sound and expression is limitless. To access it, sound designers use a foundation of music theory to control the elements of pitch, rhythm, timbre, and loudness (see Table 1 for further definition of these properties). Sound designers understand standards for these parameters and how their reshaping alters the perceived meaning of the sound. For example, high pitches, fast rhythms, and harsh timbres are typical building blocks for attention-grabbing sounds, while low pitches, slow rhythms, and smooth timbres tend to be less attention-grabbing.
The Standard Is Rising
As medical devices evolve from purely functional tools into complex, multi-sensory systems, it becomes critical for developers to strike a balance between strict compliance and exceptional user experiences. No product can be successful by focusing on just one of these aspects. In terms of alarm design, IEC 60601-1-8 lays out a formula for sound that maintains effective auditory cues for multiple categories of alarms, while leaving ample room for developers to fine-tune their alarms for optimal user experiences.
First, the guidelines specify the rhythm of an alarm. Called “burst” patterns, the alarm rhythms are made up of a series of sounds, called “pulses.” The pulses must follow a strict spacing formula to ensure the rhythms are maintained respective to their priority level. The example sounds below illustrate generic examples of burst rhythms and pulse spacings for each alarm condition.
LOW PRIORITY RHYTHM
MEDIUM PRIORITY RHYTHM
HIGH PRIORITY RHYTHM
60601-1-8 also specifies parameters for an individual note or "pulse," including the pitch, timbre, and duration. For a pulse’s pitch, the guidelines set a range of 150 Hz–1000 Hz. This is about the frequency range of a trumpet. This range establishes boundaries for the perceptible pitch of a note, or its fundamental frequency.
The pulse table also defines a range of harmonic components, which begins to specify the timbre of a sound. By requiring a minimum of four harmonics in the 300–4000 Hz range, this ensures sounds have complex timbres, which increases the audibility of a sound across multiple users, environments, and conditions. Harmonics are the additional frequencies “hidden” in a sound that give it a unique character, or quality. For example, differing harmonic quality is what separates the sound of a wooden xylophone and metal glockenspiel as they strike the same notes.
WOODEN XYLOPHONE STRIKE (dark timbre)
METAL GLOCKENSPIEL STRIKE (bright timbre)
Note the different harmonic quality, or timbre, of the same notes. By only specifying the minimum required harmonics, 60601-1-8 opens opportunities for specialized timbres and complex instrumentation that may better convey the alarm condition in a variety of environments. It should be noted that more complex, specialized timbres require higher quality, higher fidelity speaker hardware to adequately reproduce the harmonic frequencies. This relationship is a key area where developers may gain competitive advantage using well-designed sounds and hardware in their devices.
Finally, the guidelines specify duration of a pulse, and the rise and fall time of the pulse. Rise time is best illustrated by the example of plucking a violin—the sound reaches its maximum volume (or 100% amplitude) quickly, with a short rise time—and bowing a violin—the sound reaches its maximum volume more gradually, with a long rise time.
VIOLIN PLUCK (fast rise)
VIOLIN BOW (slow rise)
Note the differences in rise time, impacting the expressive nature of a sound. Fall time is similar, but relating to how the sound falls from its maximum amplitude level to silence.
A Thoughtful Design Approach to Alarms Opens Possibilities to Convey Brand Attributes and Better Alarm Usability
In a recent project, audio tones were needed as part of the total refresh of a medical device. To alleviate some of the stress-inducing properties of the device, the new design focused on improved usability, and a more "human" user experience. Earcon and music theory principles were applied to embody the user experience in sound—creating a system of sound called an audio brand language (ABL). The ABL used notes in major keys, with slow onsets, long-lasting durations, and a touch of reverb and delay to communicate the soft, “human” attributes. To reinforce the strong, engineered quality of the design, the ABL also featured notes with quick durations, atonal melodies, and tight releases. The following sounds illustrate examples of a generic ABL.
In creating alarm tones compliant with IEC 60601-1-8, sound designers applied ABL to a series of alarm families, using the specifications as the starting point. One alarm family reinforced the soft, calm, and “human” expression. It used maximal pulse spacing, longest pulse duration, low pitches, and minimal harmonics for a smooth and less urgent rhythm. This subdued approach targeted a more “human” alarm, by using the parameters to achieve an effect of warmth.
Another alarm family focused on the strong, engineered quality of product and its experience, with the soft, human qualities playing more of a background role. This family utilized detuned notes—for a wider, fuller frequency presence—layered with a strong percussive sound to create a confident and hard pulse timbre. However, to maintain some of the softness of the ABL, the notes featured medium releases, a touch of reverb, and a subtle amplitude modulation effect (tremolo).
The alarm examples in Figure 2 are recreated to help convey how this application of music theory and earcon design principles assist in the creation of user-centered, audible alarms—within boundaries of IEC 60601-1-8 guidelines. Each example starts with a "base form," which is a direct interpretation of the IEC 60601-1-8 guidelines. This is then paired with an alarm concept to illustrate how alarms can surpass compliance to achieve a unique character.
ALARM FAMILY 1—MEDIUM PRIORITY—BASE FORM (SAW WAVE)
ALARM FAMILY 1—MEDIUM PRIORITY—CONCEPT
ALARM FAMILY 1—HIGH PRIORITY—BASE FORM (SAW WAVE)
ALARM FAMILY 1—HIGH PRIORITY—CONCEPT
ALARM FAMILY 2—MEDIUM PRIORITY—BASE FORM (SQUARE WAVE)
ALARM FAMILY 2—MEDIUM PRIORITY—CONCEPT
ALARM FAMILY 2—HIGH PRIORITY—BASE FORM (SQUARE WAVE)
ALARM FAMILY 2—HIGH PRIORITY—CONCEPT
Thoughtful sound design deepens the user experience in products. When medical alerts and alarms are developed only to meet the specifications, audible feedback may be effective but misaligned with the total experience of the device, missing opportunities to strengthen the usability and emotional connection of the device. As we move towards the future of medical devices, alarms can evolve by conveying the current scenario and action required with more musical nuance. An understanding of the earcon design process and how it appropriates meaning to sound is critical to this future.
It is also important to incorporate sound design as early as possible in the development process. The ability to reproduce complex alarm timbres with greater clarity could impact speaker hardware specifications. With the appropriate hardware, an application of a sound design process, and an understanding of 60601-1-8 guidelines, acoustic experiences—and therefore user experiences—in medical devices can become more expressive, immersive, and powerful while maintaining compliance to standards.