Since the beginning of the 20th century, scientists contributed a lot of research to understand how humans locate sound sources and the results of these researches where the HRTFs . HRTFs where built on measurements by which the scientists produced sounds through speakers to the listener in specific angles and different frequencies. Microphones located in the listener's ears capture the variations that are made to the original sound wave. A function is made out from these measurements and it is drawn for both ears which represent the differences made to the amplitude of the sound waves comming from the source by changing the frequency. An HRTF is made for each azimuth position around the listener's head. Using these HRTFs we can make a system that can apply sounds around the listener in a very accurate form .  Technical Sides of HRTFs Using a technology called "Convolving", HRTFs can be used to change sound properties before outputing sound waves to the listener from the computer, which makes the listener think that the sound is comming from a location different than the real location. The process of convolving the signal, involves a multiplication process of the Discreet Fourier Transform (DFT) for the original signal by the DFT of the HRTF. Convolving : From electronic engineering point of view, convolving is the process of multiplying the original signal with specific period signal (called the "Opening" or the "Watch Window") such as the square signal. The outcome signal then represents the changing in the Opening signal variable. The Circuit The following is a short explanation of how the electronic circuit is built: (Here I'll try to simplify the terms as much as I can!!!!) The main part of the sound card is two digital to analog converters (DACs) using a specific algorithm for putting sounds in the horizontal level around the listener. The DACs used in our project are the (DAC 800) and (DAC 803) which is an 8 bit input/output DAC. The output of the DACs is then used as an input to Operation Amplifiers which transform the output current of the DACs into a voltage which drives the amplifier on the output device. As an interfacing device we used the integrated circuit (IC) 8255 which is a Programmable Peripheral Interface (PPI) that connects the 3D sound circuit to the PC. Ports addressing was made possible by using the IC 74LS138 which is a Decoder/Demultiplexer. For inputting sounds to our sound card, the ADC 804 was used. and here is the circuit's basic box diagram:
The Hardware The Software |
| MainPage | Syria | UAE | ArabicTutorial |
3D Sound System | |
Search my site: |
