Analog to Digital Conversion

There are six steps that occur in the process of analog to digital conversion. These are anti-aliasing, sample and hold, analog to digital conversion, data coding, error correction, and data recording.

1. Anti-Aliasing

An anti-aliasing filter removes frequencies that are higher than half the sampling rate using what is called a low pass filter. A low pass filter lets the low frequencies “pass" and "cut" the high frequencies. Low pass filters are sometimes called high cut filters.

Low pass filters eliminate the possibility of ghost frequencies occurring. Ghost frequencies occur when frequencies which are too high cannot be sampled correctly. Only part of the signal is sampled. When connecting these samples together they sound like low frequencies which were not in the original signal.

2. Sample and Hold

Next, the signal is temporarily stored for the length of one sample while the voltage is quantized.

3. Quantization

Quantization is the process of converting the sampled analog voltages into digital words. The digital words are made up of different combinations of binary numbers which include the numbers zero and one.

4. Data coding

Data coding separates the digital words so that they are more easily identified.

5. Error Correction

Error correction fixes small errors that may have occurred during the analog to digital process.

6.Data Storage

Data storage is the process of sequencing the data as pulses of magnetic energy. Pulse Code Modulation (PCM) is the most common code for such storage and processing digital data. Binary numbers (0 and 1) are used to store the data. The number 1 signifies a presence of energy, 0 represents an absence of energy. This data can be stored on a variety of mediums such as CD, digital tape, computer, minidisk, or DVD.

Tutorial 8: Microphones

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