In 1965, Intel cofounder Gordon Moore wrote a paper illustrating a trend that he was witnessing, where the number of transistors that could inexpensively fit on a microchip seemed to double every 18 months. This theory, now known as Moore’s Law, has held true for nearly 50 years. As microchips get smaller, so do the boards and components that integrate them.

Today’s mobile electronics are prime examples of this theory. Every two years or so, tablets and phones double in capabilities and processing power—and their memories and screen resolutions are improving at exponential rates too—while their form factors get thinner. However, these shrinking designs have had a negative effect on audio performance.

Simple physics dictates that as the surface area of a speaker cone gets smaller, the speaker’s ability to reproduce low frequencies is reduced since the cone isn’t able to move the necessary amount of air to reproduce those low frequencies at audible volumes. But to remain competitive in today’s marketplace, OEMs need to design sexy products that are thinner and sleeker than the competition.

Therefore, OEMs have no choice but to continue implementing smaller speakers into their designs. And with an ever growing catalog of headphones and Bluetooth speaker systems available to consumers, some manufacturers choose to forego any significant investment in the engineering of the internal audio systems, considering that portion of the design a last priority.

What if manufacturers could deliver significantly improved audio performance from their devices equal to much larger devices without investing millions of dollars in the audio system design? It sounds too good to be true, doesn’t it? It’s not.

By turning on/licensing and tuning the psychoacoustic audio signal processing solutions often embedded and available for implementation within many DSPs, OEMs can easily and rather inexpensively squeeze louder volume from their designs. They also can defy the laws of physics and deliver a better overall audio performance from their internal speaker or speakers, making their multimedia products far more attractive to the consumer.

How Do Psychoacoustics Improve Speaker Performance?

The way we hear sound is more than a mechanical reaction to the pressure changes associated with sound waves and how those waves hit each of our ears at varying times. It also involves sensory and perceptual events that determine how our brain processes the information received by the ears in a way that allows us to process what we’re hearing and determine from what direction and distance we’re hearing it come from.

With a thorough understanding of how the ear-brain system works and how this knowledge can be applied to audio signals to improve the human perception of sound, audio engineers from companies like SRS Labs have developed numerous practical applications for this science. Some of these applications include the ability to deliver deep bass from tiny speakers. Or, some applications take two closely spaced speakers and enable them to deliver a much wider sound field.

Psychoacoustic Bass Enhancement

Regardless of the engineering put into designing a speaker, the physical limitations associated with the size of its cone will always hinder its overall frequency response range. But there are ways to trick, for lack of a better word, your brain into hearing frequencies that physically cannot be reproduced by a speaker.

The brain fills in the visual information that is missing in the eye’s optic nerve blind spot, and it can do the same thing for sound. To take advantage of this ability, designers can apply the harmonics of low-frequency tones within a recording that cannot be reproduced by the speaker to the audio signal.

Technologies like TruBass by SRS Labs apply the overtones and undertones of these low frequencies to the mix. The brain then fills in the missing fundamentals, allowing the listener to perceive low frequencies. Psychoacoustic bass solutions, then, can enable small speakers to deliver big bass for a more enjoyable listening experience.

HRTFs To Widen Spatial Perception Of Stereo Image

Speakers near each other also suffer from varying degrees of audio limitations, including the inability to reproduce an accurate stereo image, cross-talk cancelation, and phase cancellation. In most cases, the benefit to having two speakers near each other on a small mobile device is minimal, if at all noticeable, compared to a single-speaker setup. The key to addressing this limitation is knowing how and why sound waves hit our ears at different times.

By understanding this phenomenon, called head-related transfer functions (HRTF), engineers at SRS Labs have developed algorithms designed to widen a stereo image. These algorithms then can be applied to a stereo signal in post-processing, enabling the audio image to transcend far beyond the position of the speakers within a device, allowing users to hear a more realistic stereo image and enjoy a more immersive entertainment experience.

The Next Step

These are just a couple examples of the types of limitations that psychoacoustic audio signal processing can overcome. As mobile devices continue to get smaller and more powerful, the physical limitations of the diminishing form factor will continue to pose a threat to their audio performance. And as today’s consumers become even more adamant that their mobile audio experience compares to that found on larger devices, these threats will become deterrents that limit consumer adoption of poor sounding products.

However, fixing these problems can sometimes be as easy as turning on a solution that is already available within the DSP during development. So with a little bit of engineering and the adoption of psychoacoustic audio signal processing solutions, manufacturers can overcome these limitations and develop products that work with their customers’ hearing systems to deliver a quality, immersive multimedia experience.