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Giving small speakers' audio quality a shot in the arm

Posted: 02 Sep 2010     Print Version  Bookmark and Share

Keywords:audio quality  small speaker audio  handset speaker 

Bass boost (Figure 2) takes the low-frequency content the speaker cannot reproduce and moves it an octave higher, where the speaker works well. For example: if a speaker has 3dB point of 300Hz and there is content at 200Hz, bass boost moves the content to 400Hz, which is played correctly. Given that the audio content is exactly an octave apart, the human ear and the brain are tricked into thinking that the lower frequency content is actually there (missing fundamental principle). Now, we can apply a filter to remove all the low frequency content that cannot be reproduced so they are not sent to the speaker at all. Bass boost and a high-pass filter used together can dramatically improve the bass reproduction capabilities of small speakers.

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Figure 2: Here's how bass boost works.

Audio can also be improved by virtualisation (also known as 3D) algorithms, which enhance the audio played through speakers or headphones by creating an immersive listening experience. Virtualisation algorithms increase the size of the audio field and are able to effectively create virtual surround sound even from small portable devices. They analyse the differences and commonalities of the content played through two channels of a stereo system and enhance them to make the user believe that sound is coming from all directions. These algorithms exploit the so-called head related transfer function (HRTF) that explains how sounds interact with and are interpreted by the human head, ear and brain system.

Additional algorithms focus on improving compressed audio. In this case, they strive to recover information that was lost during compression. They typically act on high frequency content (in the order ofkHz) and increase clarity. This way high-frequency sounds, like rain in a movie or a guitar solo in a song, will be reproduced in the way they were meant to be heard.

There are many audio converters (ADCs, CODECs and DACs) that support advanced audio processing capabilities. At TI, these algorithms run on an audio digital signal processors (DSP) (or miniDSP), which is integrated into the audio converter. The miniDSP is programmed by using a graphical development environment called PurePath Studio. The TLV320AIC36 is just one of the devices in the family that can be used for handsets because of its analogue inputs and outputs.

In summary, being able to reproduce high-quality audio in handsets is a complex task that requires the work of a cross-functional design team. Fortunately, electrical engineers now have the right tools: audio processing algorithms, such as the ones presented here.

- Luca Cacioli
  Portable Audio Marketing Manager
  Texas Instruments Inc.

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