Converters
Getting the computer in the speakers
"http://ikalogic.com/dac08.php"
In my last project I went over how analog signals are converted to digital signals, so in this project I will go over how digital signals can be converted back to analog. But first here is a quick review. To get an analog signal in to a digital representation we can take voltage measurements of the signal and record these measurements as binary numbers. If we use 8 bit binary words we can represent 2^8 different levels of voltage. Standard CD quality consists of using 16 bit words (for 2^16 different possible levels of voltages) and a sample rate of 44.1 kHz (44100 measurements per second). To get these measurements back to an analog signal we can can connect each bit in the word together with a combination of resistors so that every possible value for the word will produce a different voltage. The picture shows an example of an 8 bit digital to analog converter with an op amp to amplify the signal to a usable level.
High Quality Converters
http://www.oktavenaudio.com/equipment.html
High quality converters are needed when recording audio so that the reproduced audio sounds as close to the original as possible. When mixing it is even more important to have high quality converters going out to any analog equipment that might be used. But what does "good converters" even mean? According to Nyquist's theorem in order to accurately reconstruct a signal we have to take twice as many samples per second as the highest frequency we are trying to reconstruct. The human ear can hear frequencies up until right around 20 kHz, so to accurately reproduce an audio signal (at least to human ears) we have to sample it at at least 40 kHz. This is where the standard 44.1 kHz that cds are recorded at comes from - only we added 4.1 kHz for good measure. So "good converters" have to at least convert the digital signal back to analog at this sample rate. However, most high quality converters will convert at 192 kHz (or even higher!). Bit depth plays a huge role in high quality converters as well, as a high bit depth means there are more discreet levels of voltage that can be applied to the speaker to recreate the sound pressure waves. 24 Bit is most common when converting to analog.
