Low power and cost effective VLSI design for an MP3 audio decoder using an optimized synthesis- subband approach T.-H. Tsai and Y.-C. Yang Department of Electrical Engineering and National Central University, Taiwan ROC IEE Proceedings on Computers and Digital Techniques

2015/7/16 A FIXED-POINT MPEG AUDIO PROCESSOR OPERATING AT LOW FREQUENCY Abstract An optimized approach to MPEG layer-3(MP3) audio decoding is presented, with the main theme focused on the synthesis subband. Since the synthesis subband is the most power-consuming component in decoding, a cost-effective architecture is proposed based on a system-design consideration. By means of an algorithm and architecture, the synthesis subband archives a high throughput with reduced memory requirements and hardware complexity. With a two-stage pipeline architecture, it allows 100% hardware utilization and is suitable for low-power implementation. In addition, the chip design in a 0.35um process is also accomplished. It occupies a die area of about 2.7 × 3.2 mm 2 with a transistor count of 157,469 and a low-power dissipation of only 2.92mW

2015/7/16 A FIXED-POINT MPEG AUDIO PROCESSOR OPERATING AT LOW FREQUENCY What’s the problem MPEG layer-3(MP3) coding has been widely applied to current digital audio broadcasting and multimedia application  A cost-effective and low-power implementation will largely reduce the hardware and computation complexity From the MP3 decoder point of view, the computational load depends on the realization of a synthesis subband

2015/7/16 A FIXED-POINT MPEG AUDIO PROCESSOR OPERATING AT LOW FREQUENCY Outline Introduction of synthesis subband Implementation considerations and analysis Proposed method and architecture Results and comparison Conclusion

2015/7/16 A FIXED-POINT MPEG AUDIO PROCESSOR OPERATING AT LOW FREQUENCY Introduction(1) Elementary concept of MP3  Multirate subband-based coding techniques  In the encoder, it performs analysis subband filtering with 32 equally spaced filterbanks based on a psychoacoustical model  In the decoder, it performs synthesis subband filtering Most fast algorithms’ techniques interpret synthesis subband filtering as a modified discrete cosine transform (MDCT) with some additional windowing operations

2015/7/16 A FIXED-POINT MPEG AUDIO PROCESSOR OPERATING AT LOW FREQUENCY Introduction(2) One of the popular method  Translate DCT into a FFT kernel  Advantage ： Because of FFT equations’ specific symmetric and recursive property, we can reduce the number of multiplications and additions  Disadvantage ： these methods have complex control and irregular data flow which will introduce a high hardware cost The proposed design  reduced memory requirements and hardware complexity  High efficiency with 100% hardware utilization using a two-stage pipeline architecture

2015/7/16 A FIXED-POINT MPEG AUDIO PROCESSOR OPERATING AT LOW FREQUENCY Introduction(3) MP3 decoding flow  Hybrid filter bank divided into inverse modified discrete cosine transfer with dynamic windowing and overlap (DWIMDCT), and the synthesis subband filterbank

2015/7/16 A FIXED-POINT MPEG AUDIO PROCESSOR OPERATING AT LOW FREQUENCY Introduction(4) Synthesis-subband decoding flow

2015/7/16 A FIXED-POINT MPEG AUDIO PROCESSOR OPERATING AT LOW FREQUENCY Implementation analysis Design target  Delivering the required high performance at the minimum cost and the smallest silicon area  The performance is determined by real-time constraints

2015/7/16 A FIXED-POINT MPEG AUDIO PROCESSOR OPERATING AT LOW FREQUENCY Implementation analysis (cont.) MOPS = F s × ΣC × N  F s ： Sample frequency  ΣC ： Total number of numerical calculations per sample  N ： number of audio channel

2015/7/16 A FIXED-POINT MPEG AUDIO PROCESSOR OPERATING AT LOW FREQUENCY Implementation consideration In synthesis subband, IMDCT can be broken into an FFT, a data shift, preprocessing and post- processing Three considerations  The initial transformer, the real-number computation is also translated into the complex number computation  Data shift, preprocessing and post-processing still contain complex multiplications  FFT algorithms always need many multipliers, and the butterfly recursive process leads to some complex interconnection and routing

2015/7/16 A FIXED-POINT MPEG AUDIO PROCESSOR OPERATING AT LOW FREQUENCY Proposed method Normal IMDCT ： Proposed IMDCT ： Require about ¼ amount of multiplier-accumulate computations Required size for the ram buffer can be reduced to only 512 words per channel(½ amount of original)

2015/7/16 A FIXED-POINT MPEG AUDIO PROCESSOR OPERATING AT LOW FREQUENCY Architecture IMDCT IPQMF

2015/7/16 A FIXED-POINT MPEG AUDIO PROCESSOR OPERATING AT LOW FREQUENCY Architecture (cont.) Pipeline architecture

2015/7/16 A FIXED-POINT MPEG AUDIO PROCESSOR OPERATING AT LOW FREQUENCY Memory configuration (1)

2015/7/16 A FIXED-POINT MPEG AUDIO PROCESSOR OPERATING AT LOW FREQUENCY Memory configuration (2) Data conflicts in IMDCT and IPQMF

2015/7/16 A FIXED-POINT MPEG AUDIO PROCESSOR OPERATING AT LOW FREQUENCY Memory configuration (3) Memory data access with pipeline operation

2015/7/16 A FIXED-POINT MPEG AUDIO PROCESSOR OPERATING AT LOW FREQUENCY Results and comparison (1)

2015/7/16 A FIXED-POINT MPEG AUDIO PROCESSOR OPERATING AT LOW FREQUENCY Results and comparison (2)

2015/7/16 A FIXED-POINT MPEG AUDIO PROCESSOR OPERATING AT LOW FREQUENCY Results and comparison (3)

2015/7/16 A FIXED-POINT MPEG AUDIO PROCESSOR OPERATING AT LOW FREQUENCY Conclusion By means of novel algorithm and architecture, the synthesis subband has a better performance It also archives a high throughput, with a low- cost memory requirement and hardware complexity

2015/7/16 A FIXED-POINT MPEG AUDIO PROCESSOR OPERATING AT LOW FREQUENCY