How audio processing algorithms help improve sound from small speakers

Modern smartphones are slick and powerful machines. Their size varies between different models but generally speaking, state of the art devices pack lots of features into an approximately 110 x 60 x 15 mm package.

Once the display and the circuit boards are taken into consideration, not much room is left for the speakers. Now, think about a home theater and how much room a subwoofer takes. Most of you may think that these are two completely different applications and should not be even compared. This is true to a certain extent. In fact, while they are indeed wildly different applications, the content running on them is becoming more similar every day. Faster standards for mobile communications (3G, 3.5G, 4G) and their supporting networks have enabled audio and video download and playback on handsets. Customers expect that higher bandwidth comes with higher audio and video quality.

The problem is that improving audio is not easy. Handset manufacturers face various constraints, with two of the main ones being the size of the cell phone case, and how compressed the audio file is. Let's examine them.

A. Case Size
Speakers translate electrical energy into sound waves by moving their diaphragm back and forth. The diaphragm pushes the air, creating sound waves that our ears interpret as sounds. Given the above-mentioned size limitations, there is not much room left for movement. Only very small speakers with a small diaphragm and short excursion can be used.

In a world of static integrated circuits, speakers, with their need to move, are kind of 'pesky.' Small speakers cannot reproduce audio that well, and bass frequencies are the most affected. Obtaining good audio quality from a small portable consumer electronic device is a challenge that can be solved only by a cross-functional team of industrial, mechanical and electrical designers. Electrical engineers have a tool at their disposal: audio processing algorithms.

B. Compressed audio
Audio is often compressed to reduce the size of the file to be downloaded. Size reduction is achieved by using encoding algorithms (i.e., MP3). The smaller size means a loss of information and, therefore, of audio quality. Also, in this case, audio processing algorithms can help.