Research On AC-3 Encoder Algorithm And Realization On DSP

AC-3 is a digital audio coding technology developed by Dolby Lab. The technology can transfer or store as many as 5 full frequency band channels and a low frequency effect channel, the memory required is less than one channel linear PCM data in CD. Due to the flexibility of AC-3 system, in the custom electronic domain, most of movies are using this technology now, and the digital TV system of several countries, like America, also make use of this technology as the standard of audio coding.The TMS320DM642 Digital Media Processor is a high-performance fixed-point DSP of Texas Instruments. The DSP core processor has 64 general purpose 32-bit registers and 8 independent functional units with VelociTI.2 extensions: 2 multipliers and 6 arithmetic logic units (ALUs). The DM642 uses a two-level cache-based architecture and has a powerful and diverse set of peripherals.The objective of this thesis is to develop AC-3 audio encoder algorithm, transplant and optimize it based on DM642 hardware platform. At first, AC-3 encoder core arithmetic modules are presented in detail, including input filter, transient detection, MDCT, exponents encoding, and bit allocation. Here, an input filter is designed, the method of transient detection is improved, the N point MDCT fast algorithm by N/4 point FFT is deduced and realized, short windowed MDCT is conversed to the form similar to long windowed MDCT, the arithmetic on the exponent coding strategy and smoothing is carried out, and an efficient bit allocation algorithm is designed based on the relation of bit allocated and noise introduced. Then, the encoder is transplanted to DM642 platform, the encoder's efficiency is improved by making use of the characteristic of platform. By fixing point and making use of the development tools sufficiently, the problem of the high resolution requirement of IIR filter is resolved. For the moment, this encoder can run real-time on DM642 platform at 190 MHz.At last, this encoder is passed the objective test, which simulate subjective test by consideration of human hearing characteristic. Here 21 test sequences are used, the average PESQ value is 4.036 at 128kbps bitrate, and 4.220 at 320kbps bitrate.