Design Article
DSP-based audio post processing enhances audio quality
Ameet U Kalagi, Ittiam Systems Pvt. Ltd
7/28/2008 12:56 PM EDT
How do you differentiate the design of an audio player today? Consumers thinking of purchasing an audio player will certainly care about supported audio compression formats like MP3, AAC, WMA, HE-AAC, AC3 etc. But supporting multiple compression formats in audio players is no longer a differentiation but rather a compulsory feature. The real value add today comes in quality enhancements that increase listening pleasure. This article will describe popular audio-post-processing techniques and will highlight the listener value. Moreover, we will provide an overview of the technology and application of each technique and the challenge of implementing the techniques using an embedded DSP. The primary focus of the article is on portable audio players, but the same techniques can also be extended for usage in home-theater and in-Car entertainment systems.
Before diving into the article, try to visualize the effect created by audio post processing. Figure 1 shows a person listening to music using an audio player. The music is most likely composed using multiple musical instruments like drums, saxophone, guitar and violin apart from vocals.
Figure 1: Portable audio players can struggle to produce distinct sounds for each instrument and the vocals in an audio stream.
(Click on image to enlarge)
Compare this image, with Figure 2 and try to visualize the enhancement created by audio effects. Post processing can provide the enhancement shown in Figure 2. Different musical instruments sound more distinct. The vocals sound clearer. The Drums have a greater punch in them. The Guitar and the rest of instruments sound distinct and the overall perception comes closer to that of a live performance.
Figure 2: Audio post processing effects enhance the listening experience with richer more-distinct sounds.
(Click on image to enlarge)
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niranjan
7/30/2008 5:27 AM EDT
It is a very well written article. The author may please inform where can I get more information on design of HRTF and reverb.
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GauravSingh
7/30/2008 10:28 AM EDT
Nice article on post processing effects and system challenges involved
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davidgrantaustin
7/30/2008 1:23 PM EDT
Very will writen article covering the product differentiating advantages of signal processing.
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wosch
7/31/2008 9:31 AM EDT
Hallo niranjan,
I´m not the author, and I´m not sure what you are searching exactly. But try this: http://ccrma.stanford.edu/overview/ and under point "publications" (which includes a lot of stuff) the link: http://ccrma.stanford.edu/~jos/pasp/
Wolfgang Schira
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Ameet Kalagi
8/1/2008 10:42 PM EDT
Niranjan,Gaurav,David - Thanks for your appreciation. Apart from what wosch has mentioned, here is some more information on HRTF http://interface.cipic.ucdavis.edu/CIL_html/CIL_whatis.htm
On reverberation, there is a multitude of literature available online. The key points to choose a particluar approach would be 1. The delay(buffering) your application can handle and 2. The complexity of the algorithm. A rich reverb can be obtained by using multiple FDN and cross-coupling their output.
I would be interested to know if there are more such effects/post processing modules that could fit into a handheld player.
Ameet
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