Development of an MP3 player using an MP3 hardware decoder

Aleksandar L. Zoranović, Goran M. Stojanović and Veljko D. Malbascaron;a

Department of Electronics, Faculty of Technical Sciences, University of Novi Sad, Novi Sad, Serbia

E-mail: sgoran@uns.ac.rs

Abstract This paper presents an implementation of a digital audio player with the MP3 hardware decoder VS1033 as a result of a project-based course. The aim of this course is to motivate students to integrate knowledge from hardware and software in the field of microcomputer electronics and

to apply them in order to create a functional device. This device uses a very low consumption MSP430F2417 microcontroller, which has built-in peripherals for serial communication with decoder, MMC/SDC memory card and dot matrix display with a resolution of 128  64 dots. It is able to play MP3, WMA and MIDI files and has voice recording capability.

Keywords electronics teaching; hardware decoder; microcontroller; MMC/SDC card; MP3 player

The fourth-year project-based course Microcomputer electronics, presented in this paper, aims at letting the students apply knowledge obtained in previous courses and exposing them to real-life engineering work and problems. For a successful educa- tion in electronics, it is crucial that students have opportunities to perform practical activities and to lsquo;feel like engineersrsquo;. Therefore, this project-based course is designed to encourage students to create both the hardware and the software part of a func- tional device. In this paper we describe a project course based on the example of an MP3 player using an MP3 hardware decoder.

Recently, there has been a big increase in the popularity of devices capable of reproducing compressed audio formats. MPEG-1/2 Audio layer-3 (MP3) is a wide- spread format for playback of high-quality compressed audio for portable devices such as audio players and mobile phones. The attractiveness of the MP3 audio format is mostly due to its compactness compared to standard audio formats. Also, develop- ment of internet, on-line music services and file sharing clients has had a large influence on its popularity, with associated legal issues of copyright protection.¹ Because compressed audio decoding is processor demanding, in the past personal computers were mostly used in the decoding process. However, today, specialised microprocessors for decoding and reproduction of digital audio formats can be found in almost every home multimedia device and especially in portable devices. Sound compression algorithms (MP3, WMA, AAC, OGG and similar) are based on the statistical features of music and human hearing: they discard all non-audible sound details. The MP3 audio algorithm applies a psycho-acoustic model to a hybrid sub- band/transform coding scheme. In this way, less data is used for storing sound in digital format. In this process some parts of the original signal are inevitably lost in the decoding process, but an important aim is to make this loss almost imperceptible to a listener. By using a microcomputer system, decoding can be done in software

330 A. L. Zoranovicacute;, G. M. Stojanovicacute; and V. D. Malbascaron;a

or in hardware. Software decoding is usually performed on a general-purpose 32-bit RISC processor executing DSP algorithms or on a DSP processor.² Hardware imple- mentation usually implies usage of specially designed ASIC or FPGA chips.^3–5 Moreover, to consider the demand for a wireless connection to a portable MP3 player, an integrated design of an MP3 player with a Bluetooth hands-free set has been presented.⁶

In this work we present the use of a specialised microprocessor for compressed audio decoding containing communication interfaces for a simple glue-less connec- tion to a microcontroller, as the best way for students to learn principles of hardware and software co-design.

Microcomputer system

Configuration of the microcontroller system including basic components is shown in Fig. 1. The control unit is the MSP430 family microcontroller from Texas Instru- ments.⁷ It is connected with peripheral units using serial communication interfaces and synchronises their work. An SD/MMC card is used as a memory medium. The VS1033 is a single-chip hardware MP3 / WMA / AAC / MIDI decoder and ADPCM (adaptive differential pulse-code modulation) encoder, containing DSP core, memory, serial control and input data interfaces, stereo DAC, mono ADC and earphone ampli- fier. This device contains a dot matrix monochrome LCD with 128  64 dots resolu- tion and a built-in widely used KS0108 display controller.

The MSP430F2417 microcontroller presents a new generation of a very low consumption microcontrollers, incorporating the following elements: 16-bit RISC processor, memory (92 kB  256 B Flash, 8 KB RAM), peripheral units, flexible clock system. It includes two serial communication peripheral units supporting UART, SPI, I2C and IrDA interfaces.

Fig. 1 Block diagram of developed MP3 player.

Development of an MP3 player 331

This microcontroller is a good solution for this purpose because it contains enough RAM for data buffering and has all required communication interfaces realised as hardware modules. Processing speed is not sufficient for software implementation of the decoding algorithm, which is the main reason for use of a separate hardware decoder. This is a good illustration that during the project, students need to have awareness of many important hardware design issues such as trade-offs between area, speed and power consumption. The MP3 hardware decoder VS1033 uses the SPI communication protocol to communicate with the main microcontroller working as a master.⁸ The DSP core

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