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  1. 1. Recording Acoustic Guitar<br />Analog to Digital <br />Conversion<br />By Robert Howard<br />
  2. 2. Introduction<br />Why I chose this project<br />Guitar is my favourite past time<br />Absence of portable recorder<br />Current industry standards<br />24-bit with a sample rate of 96kHz is now the professional standard, offering greater headroom and definition however CD quality is limited to 16-bit 44.1kHz and so are most playback devices. <br />Existing devices<br />Mbox and PC<br />Dictaphone<br />
  3. 3. Objective<br />The electronic device I intend to build will try to capture the rich sounds of an acoustic guitar using a low voltage microphone and piezo electric pickup. The waveform will be processed by an analog to digital converter and the digital representation will then be stored on secure digital (SD) media card. <br />
  4. 4. Acoustic Guitar<br />The guitar itself acts as a whole sound system. It has a frequency response produced by the strings which is limited to a range of frequencies. <br />The guitar acts as a band pass filter with a transfer function that passes unequal amounts of energy to different parts of the frequency spectrum. The process of amplification, filtering, signal generation and pitch control all lie within the instrument itself.<br />
  5. 5. Capturing the analog signal<br />Piezo or Piezoelectric Pickups<br />A microphone changes sound waves into tiny bursts of electricity. Sound waves cause a flexible disc (diaphragm) to vibrate. <br />The up-and-down movement of a wire coil fixed to the diaphragm interacts with a magnet to produce a varying electrical current.<br />Piezo electric pickups sense vibration. They operate by sensing vibration on the surface it is attached to such as the soundboard of the guitar, as opposed to a microphone which senses the vibration in the air. The combination of a microphone and a piezo pickup will be utilized in my project.<br />
  6. 6. Microcontroller<br />Microcontrollers are special purpose computers.<br />They are embedded inside some other device so that they can control the features or actions of that device.<br />They are dedicated to one task and run one specific program. The program is stored in ROM (read-only memory) and generally does not change.<br />They require low power, usually small and of low cost.<br />
  7. 7. Analog to Digital<br />A/D conversion is the process of converting a voltage in the range of 0 to 5VDC into a number. The higher the voltage, the higher the number.<br />12-Bit Analog to Digital Conversion means a voltage from 0-5 volts will be divided into 4096 parts and be returned to the user as two values, which are recombined to make a single value from 0 to 4095.  These two values are called Least Significant Byte and Most Significant Byte. <br />Sampling rate is how frequently the analog signal is measured during the sampling process CD’s are recorded at a sampling rate of 44.1 kHz<br />
  8. 8. Secure Digital Media<br />Secure Digital (SD) cards <br /> A form of flash memory used to store data. Data is stored on a series of electronic components called NAND chips. These chips allow data to be written and stored on the SD card. As the chips have no moving parts, data can be transferred from the cards quickly, far exceeding the speeds available to CD or hard-drive media. The NAND chips in an SD card do not wear out easily, so data can be written to them thousands of times over their lifetime, making SD cards resilient and long-lasting.<br />SPI stands for Serial Peripheral Interface.<br /> SPI is a synchronous protocol that allows a master device to initiate communication with a slave device. Data is exchanged between these devices.<br />
  9. 9. Ghant Chart<br />
  10. 10. Challenges<br />Identifying the best location for microphone and pickup<br />Capturing the range of harmonics which give the acoustic guitar its unique sound<br />Balancing the quality of recording with storage capabilities also matching read write speeds<br />Using C computing language to program the microcontroller<br />Implementing the Serial Peripheral Interface<br />http://rha2d.pbworks.com<br />