Real-time Digital Signal Processing Demonstration Platform

In order to demonstrate various digital signal processing (DSP) algorithms to students or potential students, a program was developed that runs in real-time on low cost, commercially available hardware. The program includes several common DSP algorithms such as lowpass filter, highpass filter, echo, reverb, quantization, aliasing, simple speech recognition, and fast Fourier transform (FFT). The program allows the user to easily switch between algorithms, to adjust the parameters of the algorithms, and to immediately hear the results. The demonstration hardware consists of the TMS320C5515 eZdsp USB Stick, a powered microphone, an audio source such as an MP3 player or cellphone, and speakers. Undergraduate electrical engineering students were shown the demonstration and were surveyed to determine which algorithms they found most interesting. The C language source code for the software is available from the author for free, so this program can be modified by instructors who wish to make their own demonstrations or used as a convenient starting point for student projects. Introduction The material in a DSP course is often highly theoretical and mathematical, and so it is useful to connect the theory to real-world applications with laboratory experiments, simulations, or demonstrations. Fortunately, there are many interesting applications of DSP that can help captivate students and motivate them to learn the theoretical material. Perhaps the best way to expose students to the applications of DSP is with a laboratory course, but at some institutions a full laboratory course in DSP is not feasible due to time, space, and funding constraints. Alternatives to laboratories include projects, simulations, and demonstrations. Although many DSP algorithms can be demonstrated using offline (not real-time) processing, some demonstrations are just more compelling if they operate in real-time. A real-time demonstration with audio signals, for example, can be more interesting because the user can use his/her own voice as the input and hear the results immediately. Many authors have explored various ways to demonstrate DSP concepts and algorithms. Some have used software such as MATLAB 2, 3, 4, , LabView 5, 6, , J-DSP, or DirectX that runs on a personal computer (PC). Some have incorporated commercially available DSP boards including the TMS320C6713 DSK 11 (about $400), OMAPL138 Low Cost Development Kit 13 (about $200), Logic PD Zoom OMAP-L138 Experimenters Kit (about $500), and DSK5510 (about $400). Some have combined DSP boards with software such as MATLAB/Simulink , winDSK 18, 19, , J-DSP, and LabView. Courses in DSP have also been taught using FPGA boards 24 and microcontrollers . This paper describes a real-time demonstration platform based on the TMS320C5515 eZdsp USB Stick Development Tool. This DSP board, which is available for about $80, is less expensive than any of the other DSP boards listed above, yet it has all the features necessary to conveniently demonstrate DSP with audio signals, including a high quality audio interface, a small graphical display, two buttons for user input, and five LEDs. Compared to the more expensive boards, this board does have some disadvantages, including a slower processor with no floating-point hardware and less on-board memory, but it is more than adequate for demonstrating audio applications in real-time. Furthermore, the source code for the software is available from the author for free, which may be helpful for others who wish to develop their own demonstrations or for student projects. Hardware Manipulating audio signals is an excellent way to illustrate DSP concepts. This approach allows students to directly experience the effect of various algorithms and to hear the effect of using different parameters values. As shown in Figure 1, the hardware required for the audio demonstrations is fairly simple. The audio source can be any device that has line level or headphone output, such as MP3 player, cellphone, or PC. The output of the DSP board can be monitored with headphones or inexpensive computer speakers. The PC is used to download the program and to provide power for the DSP board. However, if the program is written to the flash memory on the DSP board, then the PC could be replaced with a USB power supply. Audio Source (MP3 player, Cellphone, PC, etc.) TMS320C5515 eZdsp USB Stick